List of Schemes Scheme 1.1 The common examples of metallocene complexes 2 Scheme 1.2 Aryloxide and ketimide titanium half-sandwich catalyst precursors used for styrene–ethylene copolym
M ETALLOCENE
The name “metallocene” has been known in the early 1950s as a more elegant replacement for the term “iron sandwich” which was initially used to describe the structure of ferrocene (biscyclopentadienyliron) [1,2] Metallocene is defined as an organometallic coordination compound obtained as a cyclopentadienyl (Cp) derivative of a transition metal or metal halide The metal is bonded to the Cp ring by electrons moving in orbital extending above and below the plane of the ring [3]
The first efficient metallocene catalyst for polymerizing ethylene was discovered in 1976 [4] After that, one of the most fascinating developments in the field of transition metal polymerization has been the discovery by Sinn and Kaminsky of homogeneous metallocene-based coordination [4-7] So, metallocene catalysts systems for polymerization of olefins are composed of a metallocene complex and a cocatalyst They are termed “single-site” catalysts because each molecule of the metallocene complex forms one catalytic active site [8-10]
Historically, it is classified into four groups on the basis of the structure:
Bent-metallocene, Ansa-metallocene, Half-metallocene and Constrained Geometry catalyst as shown in Scheme 1.1
Ansa-Metallocene IPP, SPP (Hoechst)
Scheme 1.1 The common examples of metallocene complexes
In the early 1980s, Ewen and Brintzinger discovered a new kind of metallocene catalyst called ansa-metallocene because the two Cp ligands are joined by a covalent bridge [11] It is able to produce highly stereoregular polypropylene and has been the most common chiral metallocene catalyst
In 1985, highly syndiotactic polystyrene was first synthesized by Ishihara at Idemitsu, using homogeneous titanium half-sandwich catalyst [12] This success of titanium half-sandwich catalysts to promote syndiospecific styrene polymerization was reported in the mid-1980s naturally led to some investigations of these catalytic systems for styrene–ethylene copolymerization [13] Other titanium half-sandwich catalysts, in which one of the chloride ligand was replaced by another anionic ligand X, either an aryloxide (complexes 1-12, Scheme 1.2) or a ketimide group (complexes 13-15), were reported to be efficient catalysts for styrene–ethylene copolymerization [14-18]
Scheme 1.2 Aryloxide and ketimide titanium half-sandwich catalyst precursors used for styrene–ethylene copolymerization
In the early 1990s, a new family of active polymerisation catalysts was developed by formally exchanging one cyclopentadienyl ring by an amido moiety These are often referred to as constrained geometry complexes CGCs, given the chelate bite angle imposed by the cyclopentadienyl and amido donors [19] Bercawand co-workers [20] and Okuda et al [21] were the first authors described the synthesis of those complexes However, the term constrained geometry complex was originally coined by Stevens et al He and coworkers at Dow made the remarkable developments related to the metallocene catalyst system [22]
The main feature of metallocene catalysts is that the cyclopentadienyl ligands are connected by a bridge; therefore, they could not rotate freely, and this granted rigidity to the molecule The application of ŋ 5 – cyclopentadienyl ligands is particularly attractive due to the wide variety of potentially synthetically useful organometallic complexes containing this ligand, the impressive bond strengths with which this ligand is attached to transition metals and the large array of possible structural modifications of the ligand which are synthetically approachable [23] Subsequent investigations on this and other soluble catalysts have been conducted, and many catalyst systems have been developed and studied
There are four main advantages that distinguish metallocene catalysts from other catalysts in the polyolefins industry [24] First, they can polymerize many vinyl monomers, including those with polar functionality and steric hindrance Second, they can produce extremely uniform polymers and copolymers of narrow molecular weight distribution and narrow compositional distribution [25] Third, they can control vinyl unsaturation and are expected to achieve great improvements in properties such as paintability, wetability, and adhesion between the matrix polymer and reinforcing fibers [26] Last, they can polymerize α-olefins with very high stereoregularity [27]
Indeed, the important key issues for a successful design of an efficient transition metal catalyst for (co)polymerizations are as follows: (a) catalytic activity, (b) molecular weight and molecular weight distribution, (c) comonomer (e.g α-olefin, styrene, cyclic olefins, etc.) incorporation, (d) others such as branching (short, long), structure/performance relationship.Both steric and electronic factors of the complexes were affected toward the catalytic activity and molecular weight [28] So, designing efficient transition metal complex catalysts for precise olefin polymerization is far from over.
D INUCLEAR METALLOCENE
During the past 25 years, metallocene complexes have been extensively studied as catalysts for the homogeneous and heterogeneous polymerization of α-olefins.[2,5,11,29-35] However, polyolefins produced using common metallocene catalysts process, in general, has narrow molecular weight distribution (MWD), causes difficulties in industrial processing On the contrary, polyolefins with high Mw and broad MWD, ideal polymers with superior physical properties are easy to process [36,37] Therefore, it is an attractive research project to produce polyolefins with high Mw and broad MWD Several methods have been reported to control the Mw an MWD of polymers such as polymerization in a series of reactors with different polymerization conditions and polymerization in a single reactor with a mixture of individual mononuclear catalysts However, these methods also cause problems, e.g in miscibility [38] in processing and they increase the capital costs
Therefore, it was the intention to solve this problem with a variety of multinuclear including di-, tri-, and tetra-nuclear metallocene complexes as catalyst precursors
In recent years, a variety of dinuclear metallocene catalysts has been developed for olefin polymerization due to their potential of tailoring the polymer properties in this direction [39-41] The common examples of metallocene complexes were shown in Scheme 1.3
Petersen [42] and Royo [43,44] prepared a variety of dimethylsilyl bridged homodinuclear metallocene complexes of titanium and zirconium Muelhaupt [45] first studied olefin polymerization using phenylene bridged dinuclear zirconocenes and showed cooperative effects In 1996, Green [46] reported a series of homo- and hetero-dinuclear metallocene catalysts for the polymerization of ethylene and propylene Soga et al [47] prepared biphenyl bridged dinuclear zirconocenes with an excellent thermal stability and an extremely high catalytic activity for ethylene polymerization Alt [48] reported on a series of asymmetric alkylidene bridged dinuclear metallocene complexes of zirconium and hafnium for ethylene polymerization Their results verified their hypothesis that the PE obtained from those dinuclear metallocene complexes has broader MWD than that produced with corresponding mononuclear metallocene complexes [49]
Scheme 1.3 The common examples of dinuclear metallocene complexes
Systematic studies of dinuclear metallocenes as catalysts for olefin polymerization show an increasing polymerization activity with longer bridges between the active centers [41] Comparing with the rich chemistry of metallocene, dinuclear metallocenes have been paid attention to two respects First, dinuclear metallocenes can be a new kind of metallocene catalyst for olefin polymerization which could be potentially useful in catalyst for olefin if two metal centers show cooperative electronic and steric effects on catalytic reaction Second, dinuclear metallocenes could be a good model to probe reaction characterization of an immobilized metallocene because the immobilized metallocene could be regarded as a multinuclear metallocene on support On the basic of the experience, our group have accomplished in the field of dinuclear metallocene over the last several years (Scheme 1.4, Scheme 1.5, and Scheme 1.6) [50-63] In 1996, we have synthesized a series of dinuclear metallocenes containing polysiloxane units as a bridging ligand and conducted ethylene polymerization with these complexes to examine not only the effect of bridge nature on catalyst property, but also the characteristics of dinuclear metallocenes We described the synthesis and ethylene/styrene copolymerization studies of new kinds of dinuclear half-sandwich metallocenes connected with two structurally different bridging ligands In 2000, we made a report on the preparation of polymethylene-bridge half-titanocenes and investigation of their styrene polymerization properties In 2006, we reported efficient synthetic route to synthesize dinuclear half-titanocenes with xylene bridge and the results of styrene polymerization using these catalysts with the emphasis on the nature of bridging ligand Recently, in 2009, we have described an efficient preparative route to make four novel dinuclear half-titanocenes with meta- and ortho-xylene bridges in order to understand the influence of the geometric arrangement of dinuclear metallocenes on catalytic behavior These researches have been designed to figure out how the bridge stiffness can operate on the property of the dinuclear half-titanocene and exhibit some meaningful aspects to point out the effect of space orientation of the two active sites For better understanding about the effect of bridge on catalyst behavior, the dinuclear half-titanocene will be tried in polymerization of IBVE, a polar vinyl monomer
Because of the more complicated synthesis route, polymerization properties of the dinuclear complex that holds two CGC fragments through the bridging ligand have not been explored much until now In 2002, Mark’s group reported synthesis of the ethylene bridged dinuclear zirconium CGC to probe copolymerization of ethylene and α-olefin [64] They attributed the higher copolymerization capability of CGC to the nuclearity effects of the DCGC due to the close spatial proximity between two active sites After that, in 2004, Marks described DCGC that exhibit much better activity for styrene copolymerization [65] This styrene incorporation ability improvement was also observed in dinuclear catalysts featuring longer bridges In 2003, we have synthesized a series of dinuclear CGC as a new kind of dinuclear metallocene catalyst The rigid bridges can efficiently suppress the free movement of metallocene units in the same molecule and avoid an intramolecular deactivation
Therefore, influence of rigid bridge on olefin polymerization is the interested topic nowadays For those reasons, we have been designing new DCGC based on combination of mononuclear CGC properties with the natural properties of rigid bridge and using them in ethylene copolymerization.
C OCATALYST
A key to the high polymerization activity of single site catalysts is the cocatalysts.
Metallocenes by themselves are not active for polymerization, and they require a cocatalyst to generate the active species MAO is the most important cocatalyst which activates the metallocenes polymerization [4-7] The intensive search for the active cocatalyst responsible for this activation led to the isolation of methylaluminoxane (MAO) in 1977, a component in which aluminium and oxygen atoms are alternately positioned and free valences are saturated by methyl groups [5,6] If metallocenes, especially zirconocenes, are combined with MAO, the resulting catalyst can polymerize olefins 10- 100 times faster than those used in most active Ziegler-Natta systems [7]
Ti Cl Cl Cl Si
Scheme 1.5 Our dinuclear metallocenes (continue)
Scheme 1.6 Our dinuclear metallocenes (continue)
Alkylaluminoxanes, which are prepared by careful treatment of trialkylaluminonium with water, are usually defined as compounds containing at least one bridging oxo group between two or more aluminium centers They constitute mixtures in which appear species such as R2AlO-[Al(R)-O]x-AlR2 and [Al(R)-O]x (x=2-20), with or without branching of the –[Al(O-O)]- type; the mentioned species are three-dimensional cage compounds with four-coordinate aluminium centers [4-7]
MAO is necessary for elimination of all kind of impurities existing in the polymerization medium and generating the active species Catalyst activity increases with an increasing Al/Mt ratio [7] A large excess of methylaluminoxane (Al/Mt ratio >500) is generally required for acceptable activity [66]
However, MAO is a high cost compound, which has led to the investigation of the use of alternative activators such as trialkylaluminums, [67] boron-based compounds, [68] and catalyst supports with active surfaces Even if the role of the cocatalyst is to act as a Lewis acid, that is, to create and maintain the necessary coordinative unsaturation and electron deficiency at the metal center, because not
O O all Lewis acids are effective cocatalysts For instance, BCl3, BF3, PF5, SbF5, Me3SnCl, and Me3SiCl are not suitable candidates, mostly because the halide atoms can either strongly coordinate or irreversibly transfer to the Ti cation [12,69] In summary, as in olefin polymerization, both the nature and the ion-pair interactions are crucial to devise efficient cocatalysts.
M ECHANISM OF COORDINATION POLYMERIZATION
In the coordination polymerization of olefins, the active site of the catalyst usually contains an alkyl group as the metal substituent forming with the metal an Mt-C active bond of the σ type The polymerization consists in the insertion of the coordinated monomer into this bond with the regeneration of a metal-carbon bond of the same character [70] The initiation and the propagation steps, involving monomer coordination and enchainment by insertion of the coordinating monomer (Scheme 1.7), is commonly accepted for olefin polymerization with coordination catalysts
Scheme 1.7 The coordination polymerization of olefins
However, there is no general uniform mechanism that might operate in all polymerization systems and under all polymerization condition applied For most common polymerizations under common conditions, the insertions of the coordinated monomer is assumed to be the rate determining step [70]
Scheme 1.8 Mechanism for monomer insertion in α-olefin polymerization with coordination catalysts
Px=Pn and/or Pn+1, M=CH2=CHR, □=coordination vacancy
Most studies agree that the insertion step is the rate controlling one The insertion of coordinated olefin proceeds very fast; an energetically favorable spatial arrangement of ligands, metal-carbon bond and coordinated monomer determines high rates of insertion The insertion involves the cleavage of the formation of a new metal-carbon bond It is characteristic that olefin polymerization with both heterogeneous and homogeneous catalysts involve cis-insertion of the C=C bond in the coordinated olefin into the Mt-C bond in all cases, irrespective of the monomer enchainment mode (1,2 or 2,1) and the tacticity of the poly (α-olefin) formed A cis-opening of the olefin double bond has been proved conclusively by using deuterated propylene for the polymerization and determining the chain microstructure of the polymers formed
A considerable amount of research has been directed towards the comprehension of polymerization mechanism The nature of the true active species is not yet fully elucidated and continues to be the matter of extensive studies Consequently, it is now generally admitted that the active species is a cationic Ti(III) complex of the type [CpTiR] + formed in three steps: (1) alkylation by MAO or AlR3, (2) cationization by ligand abstraction, and (3) reduction of Ti(IV) to Ti(III); though, the exact order of those steps is still unclear [12]
After inserting olefin into the Mt-C bond in cationic metallocene, the polymer chain may be located in a position previously occupied by the coordinating olefin molecule (chain migratory insertion mechanism) or it may skip back to its starting position (chain stationary insertion mechanism) prior to the subsequent coordination of the next olefin molecule, i.e whether or not the catalytic site undergoes back-skipped isomerization
Polymerization termination occurs predominantly by β-H elimination and chain transfer to the aluminum cocatalyst The β-H elimination seems to be predominant for syndiospecific styrene polymerization rather than for ethylene polymerization by metallocenes because of a smaller activation barrier
It can be concluded that the mechanism of olefin polymerization by metallocene catalyst follows the mechanism of most chain polymerization processes; the reactions can be divided into three distinct steps: chain initiation, chain propagation and chain termination.
T HE SCOPE OF THESIS
As said above, a variety of dinuclear metallocene catalysts has been developed rapidly for olefin polymerization due to its possibility of tailoring the polymer properties, such as molecular weight, molecular weight distribution as well as stereochemistry through cooperative effects between two metal centers, ligand structures and the nature of the bridge This thesis focuses on synthesis of new dinuclear catalyst which can enhance the polyolefin properties and investigates effect of catalyst structures on polymerization behavior Besides of the first chapter of introduction, the remaining content of thesis includes four chapters corresponding to four tasks as following
Chapter 2: Synthesis catalyst to apply to preparation of polymer is task 1 A series of dinuclear half titanocene was synthesized with the reported route Beside of dinuclear half metallocene, dinuclear constrained geometry catalyst, which is able to control both molecular weight of polyethylene and copolymerizability of ethylene, also has the main role in metallocene researches In this chapter, the designed structure and the route of preparation of new dinuclear CGC with a series of rigid bridges which may have different length of alkyl branch, different volume between two CGCs will be reported The bridge is able to interact with polymerization active site in order to improve copolymerizability of monomer and control molecular weight of polyethylene simultaneously
Chapter 3: In our laboratory, many new dinuclear half metallocene polymerization systems have been developed to make syndiotactic polystyrene as well as polyethylene [50-63] However, these catalysts have rarely been applied to polymerize polar vinyl monomers A specific example of poly(vinyl ethers) is poly(isobutyl vinyl ether), has found the economically important application as adhesives, impregnating agents for textile, paper, leather, surface coatings [71,72] So, the task 2 is that a series of dinuclear half metallocene with different polymethylene bridges were synthesized and used in isobutyl vinyl ether polymerization All of these results will be shown in this chapter
Chapter 4: Using new catalyst prepared in task 1, ethylene/styrene copolymerizations were tried with some reaction conditions to find the effect of bridge ligand on two metallocene active sites, which is significant to derive polymerization properties of metallocenes Polymer were analyzed by GPC, NMR, DSC to measure molecular weight of polyethylene, sequence of copolymer, and contents of comonomer in ethylene copolymers This is task 3
Chapter 5: This chapter investigates ethylene/1-hexene copolymerizations, task 4, using catalysts in task 1 under a variety of reaction conditions such as temperature, catalyst concentration, comonomer concentration, amount of cocatalysts, etc
According to these polymerization conditions, the effective conditions were chosen to consider the influence of catalyst structure on polymerization behavior and properties of polymer.
I NTRODUCTION
The search for new α-olefin copolymerization catalysts based on transition metal complexes is a field of major interest involving many academic and industrial research groups CGCs activated by methylaluminoxane (MAO) have shown capability of producing copolymers with superior processing/mechanical properties such as long chain branching and high degrees of comonomer incorporation than the conventional Ziegler–Natta catalysts [1] In recent years, a variety of binuclear constrained geometry catalysts have been developed rapidly for olefin polymerization [2-10] The reason could be seen clearly that the ligands surrounding the metal play a crucial role in determining the activity as well as the stereospecifity of the catalyst, by affecting the steric and electronic properties at the metal Up to now, there are two kinds of bridges in binuclear metallocene catalysts with some short or long bridges, namely flexible bridges as polymethylene, [11,12] polysiloxane, [13,14] and rigid bridge containing phenyl rings [15] or double bridges [16,17] From the standpoint of bimolecular deactivation, [18] the rigid bridge of binuclear metallocene is valuable to be investigated in detail, because these metallocenes could avoid intermolecular deactivation Our research interest is focused on phenyl ring bridged binuclear metallocene catalysts due to their convenient modification and clear electronic and steric effect According to these advantages, this project develops the new catalyst structure base on the xylene bridge The specific structure was show in Scheme 2.1
Type 1 Various alkyl substituents on xylene bridges
Type 2 Various lengths of bridges
In type 1, we hope that the different steric and electronic of alkyl substituents will be touched on the active site to change the catalytic properties Besides of that, in type 2, the various lengths of bridges will differently modify the catalyst behavior.
S YNTHESIS PROCEDURES
The researcher is already fully trained to successfully synthesize 6 catalyst structures which were labeled as above The general procedure to synthesize was performed in Scheme 2.2 All manipulations were performed under a dry, oxygen-free atmosphere using standard glove box and Schlenk techniques with a double manifold vacuum line Nitrogen gas was purified by passing through a column of molecular sieve and Drierite (8 mesh)
Diethyl ether and hexane were purified by using MBRAUN MB-SPS-800 series
Tetrahydrofuran (THF) and toluene were distilled from sodium/benzophenone ketyl prior to use
1-Bromohexane, 1-bromooctane, 2-bromopropane, 1,4-dichlorobenzene, magnesium, 1,3-bis(diphenyl phosphino)propane nickel(II) chloride, chloromethyl methyl ether, 30% fuming sulfuric acid, 1,4-dichlorobenzene, α,α’-Dibromo-p-xylene, indene, n-BuLi (2.5 M in hexane) and silver chloride 99.9% were purchased from Aldrich and used as received
1,4-bis(2-chloroethylbenzene) were purchased from TCI company and used as received Dichlorodimethyl silane and tert-Butyl amine, purchased from Aldrich, was distilled from calcium hydride prior to use Titanium (III) chloride tetrahydrofuran complex (TiCl3(THF)3) were prepared by literature method [19]
Scheme 2.2 The route of synthesizing catalysts
1H-NMR and 13 C-NMR spectra were recorded on Bruker DPX-300 FT-NMR spectrometer using CDCl3 Elemental analysis was recorded by EA1112 (FISONS Instrument, Italy)
New structures of bridges were designed and synthesized according to organic method as the Scheme 2.3
4a-6a are known chemicals which can be purchased from Aldrich and TCI companies
1a (R = iso-propyl) 2a (R = n-hexyl) 3a (R = n-octyl) Scheme 2.3 Synthesis of ligands a Synthesis of 1,4-dialkylbenzene,1x-3x
The alkyl magnesium bromide was synthesized by dropping alkyl bromide in ether to magnesium in ether at room temperature over 20 minutes The mixture was refluxed for three hours, then, cooled to room temperature
This Grignard reagent was added dropwise to solution of 1,4 dichrolobenzene (4- chlorotoluene) and dichloro[1,3-(diphenylphosphino)propane]nickel(II) in 200 ml of dry ether below 0 0 C over a period of 30 min The ice-bath was removed and the ether began to boil after an induction period of about 30 min The mixture was refluxed for 1 day, cooled to 0 0 C and carefully quenched with water, followed by
2M HCl The usual work-up gave the light yellow oil (1,4-dialkylbenzene)
Compound 1x: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.14(s, 4H, C6H4), 2.86(m, 2H, CH), 1.25(d, 12H, (CH3)2),
Compound 2x: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.11(s, 4H, C6H4), 2.62(t, 4H, CH2), 1.64(m, 4H, CH2), 1.32(m, 12H, (CH2)3), 0.89(m, 6H, CH3)
Compound 3x: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.11(s, 4H, C6H4), 2.62(t, 4H, CH2), 1.64(m, 4H, CH2), 1.32(m, 20H, (CH2)5), 0.89(m, 6H, CH3) b Synthesis of 2,5-Bis(Chloromethyl)-1,4-dialkylbenzene,1a-3a
2,5-Bis(chloromethyl)-1,4-dialkylbenzene (1a – 3a) was synthesized by adding slowly 30% fuming sulfuric acid to solution of 1,4-dialkylbenzene and chloromethyl methyl ether at 10 0 C After stirring 1 day at room temperature, the reaction mixture was poured into ice water Resulting crystals were separated and dry water under vacuum, then purified by silica-gel column chromatography (using hexane as a solvent) The recrystallization from hexane gave white solid (yield 40%)
Compound 1a: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.22(s, 2H, C6H2), 4.61 (s, 4H, CH2Cl), 3.25 (m, 2H, CH), 1.27(d, 12H, (CH3)2)
Compound 2a: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.14 (s, 2H, C6H2), 4.57 (s, 4H, CH2Cl), 2.65 (t, 4H, CH2), 1.62 (m, 4H, CH2), 1.35 (m, 12H, (CH2)3), 0.89 (m, 6H, CH3)
Compound 3a: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.14 (s, 2H, C6H2), 4.57 (s, 4H, CH2Cl), 2.65 (t, 4H, CH2), 1.62 (t, 4H, CH2), 1.35 (m, 20H, (CH2)5), 0.89 (m, 6H, CH3)
2.2.4 Synthesis of [Ind] 2 {(CH 2 ) n [(R) 2 C 6 H 2 ] (CH 2 ) n }, 1b-6b
2,5-Bis(chloromethyl)-1,4-dialkylbenzene in THF was dropped slowly into solution of IndLi salt in THF at -78 o C The reactor was warmed to room temperature, then heated up 60 0 C in 48 h THF was volatilized in vacuo at least 4 h
Product was separated by filter through celite with hexane in case of 2b, 3b and ether in case of 1b, 4-6b The light yellow solution was removed solvent to get light yellow powder (Yield >98%)
Compound 1b: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.46(d, 2H, C9H7), 7.41(d, 2H, C9H7), 7.29 (t, 2H, C9H7), 7.19(t, 2H, C9H7), 7.01(s, 2H, C6H2), 5.80(s, 2H, C9H7), 3.85(s, 4H, CH2), 3.27(s, 4H, C9H7), 3.06(m, 2H, CH), 1.17(d, 12H,(CH3)2)
Compound 2b: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.45(d, 2H, C9H7), 7.38 (d, 2H, C9H7), 7.31(t, 2H, C9H7), 7.18(t, 2H, C9H7), 6.99(s, 2H, C6H2), 5.87(s, 2H, C9H7), 3.82(s, 4H, CH2), 3.30(s, 4H, C9H7), 2.51(t, 4H, CH2), 1.48(m, 4H, CH2), 1.19(m, 12H, (CH2)3), 0.82(m, 6H, CH3)
Compound 3b: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.46(d, 2H, C9H7), 7.38 (d, 2H, C9H7), 7.31(t, 2H, C9H7), 7.20(t, 2H, C9H7), 6.99(s, 2H, C6H2), 5.87(s, 2H, C9H7), 3.82(s, 4H, CH2), 3.30(s, 4H, C9H7), 2.50(t, 4H, CH2), 1.48(t, 4H, CH2), 1.18(m, 20H, (CH2)5), 0.82(m, 6H, CH3)
Compound 4b: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.49(d, 2H, C9H7), 7.32 (d, 2H, C9H7), 7.30(t, 2H, C9H7), 7.29(t, 2H, C9H7), 7.21(s, 4H, C6H4), 6.16(s, 2H, C9H7), 3.91(s, 4H, CH2), 3.38(s, 4H, C9H7)
Compound 6b: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.46(d, 2H, C9H7), 7.38 (d, 2H, C9H7), 7.32(t, 2H, C9H7), 7.26(t, 2H, C9H7), 7.13(s, 4H, C6H4), 6.22(s, 2H, C9H7), 3.32(s, 4H, C9H7), 2.86(s, 4H, CH2 ), 2.81 (s, 4H, CH2)
2.2.5 Synthesis of [Me 2 SiCl(Ind)] 2 {(CH 2 ) n [(R) 2 C 6 H 2 ] (CH 2 ) n },, 1c-6c
The solution of n-BuLi 2.5M was dropped directly in solution of 2b, 3b in hexane at -78 o C The light brown suspension was stirred over 1 h at nature and heated up 60 o C for 12h Then the light yellow salt was filtered with hexane and removed solvent at reduce pressure overnight (Yeild 98%)
Whereas, di-lithium salt of 1b and 4b-6b were prepared in THF solvent The solution of n-BuLi 2.5M was dropped directly in solution of 1b and 4b-6b at -78 0 C
The solution was stirred at room temperature in 1 hour and heated up 60 0 C for 12 hours, then cooled to room temperature before removed THF The salt was purified by filtering with hexane and drying under vacuum pressure
A solution of Me2SiCl2 in ether was treated dropwise over 15-20 min with a solution of dilithium salt at –78 0 C After 6 hours of reaction at room temperature, the suspension was removed ether and filtered through the celite with hexane to get the yellow solution The yellow sticky oil was collected after volatilized hexane
Compound 1c: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.57(d, 2H, C9H6), 7.48(d, 2H, C9H6), 7.32(t, 2H, C9H6), 7.23(t, 2H, C9H6), 7.09(s, 2H, C6H2), 5.88(s, 2H, C9H6), 3.95(s, 4H, CH2), 3.59(s, 2H, C9H6 ), 3.06 (m, 2H, CH), 1.12(d, 12H, (CH3)2), 0.16(s, 12H, Si-CH3)
Compound 2c: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.57(d, 2H, C9H6), 7.41(d, 2H, C9H6), 7.31(t, 2H, C9H6), 7.25(t, 2H, C9H6), 6.96(s, 2H, C6H2), 6.00(s, 2H, C9H6), 3.89(s, 4H, CH2), 3.60(s, 2H, C9H6 ), 2.51 (t, 4H, CH2), 1.53(m, 4H, CH2), 1.19(m, 12H, (CH2)3), 0.86(m, 6H, CH3), 0.18(s, 12H, Si-CH3)
Compound 3c: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.57(d, 2H, C9H6), 7.39(d, 2H, C9H6), 7.29(t, 2H, C9H6), 7.22(t, 2H, C9H6), 6.95(s, 2H, C6H2), 6.00(s, 2H, C9H6), 3.89(s, 4H, CH2), 3.60(s, 2H, C9H6 ), 2.50 (t, 4H, CH2), 1.47(m, 4H, CH2), 1.18(m, 20H, (CH2)5), 0.85(m, 6H, CH3), 0.18(s, 12H, Si-CH3)
Compound 4c: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.54(d, 2H, C9H6), 7.34 (d, 2H, C9H6), 7.23(t, 2H, C9H6), 7.21(t, 2H, C9H6), 7.18(s, 4H, C6H4), 6.23(s, 2H, C9H6), 3.91(s, 4H, CH2), 3.62(s, 2H, C9H6), 0.17(s, 12H, Si-CH3)
Compound 5c: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.58(d, 2H, C9H6), 7.48(d, 2H, C9H6), 7.28(t, 2H, C9H6), 7.21(t, 2H, C9H6), 7.00(s, 4H, C6H4), 6.66(s, 2H, C9H6), 3.74(s, 2H, C9H6), 0.24(s, 6H, Si-CH3), 0.18(s, 6H, Si-CH3)
Compound 6c: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.59(d, 2H, C9H6), 7.50(d, 2H, C9H6), 7.36(t, 2H, C9H6), 7.28(t, 2H, C9H6), 7.16(s, 4H, C6H4), 6.37(s, 2H, C9H6), 3.73(s, 2H, C9H6), 3.01(m, 4H, CH2), 2.99 (m, 4H, CH2), 0.20(s, 12H, Si-CH3)
2.2.6 Synthesis of [(NH t Bu)(Me 2 Si)(Ind)] 2 {(CH 2 ) n [(R) 2 C 6 H 2 ] (CH 2 ) n }, 1d-6d
Tert-butylamine (2.72ml, 25.9mmol) was added slowly to solution of 1c-6c in THF at 0 0 C The reactor was warmed to room temperature and then heated up 60 0 C overnight The product 1d-6d was purified by the same process with 1c-6c after removing THF (Yield >98%)
Compound 1d: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.57(d, 2H, C9H6), 7.48(d, 2H, C9H6), 7.32(t, 2H, C9H6), 7.23(t, 2H, C9H6), 7.09(s, 2H, C6H2), 5.88(s, 2H, C9H6), 3.92(s, 4H, CH2), 3.42(s, 2H, C9H6), 3.08(m, 2H, CH), 1.15(s, 18H, t-Bu), 1.13(d, 12H, (CH3)2), 0.60(s, 2H, NH), -0.05(d, 6H, Si-CH3), -0.19(d, 6H, Si-CH3) Compound 2d: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.57(d, 2H, C9H6), 7.41(d, 2H, C9H6), 7.31(t, 2H, C9H6), 7.25(t, 2H, C9H6), 6.96(s, 2H, C6H2), 6.00(s, 2H, C9H6), 3.88(s, 4H, CH2), 3.45(s, 2H, C9H6), 2.51(t, 2H, CH2), 1.53(m, 4H, CH2), 1.19(m, 12H, (CH2)3), 1.17(s, 18H, t-Bu), 0.86(m, 6H, CH3), 0.63(s, 2H, NH), -0.05(d, 6H, Si-CH3), -0.19(d, 6H, Si-CH3)
Compound 3d: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.57(d, 2H, C9H6), 7.39(d, 2H, C9H6), 7.29(t, 2H, C9H6), 7.22(t, 2H, C9H6), 6.95(s, 2H, C6H2), 6.00(s, 2H, C9H6), 3.88(s, 4H, CH2), 3.45(s, 2H, C9H6), 2.51(t, 2H, CH2), 1.48(m, 4H, CH2), 1.19(m, 20H, (CH2)5), 1.16(s, 18H, t-Bu), 0.86(m, 6H, CH3), 0.63(s, 2H, NH), -0.05(d, 6H, Si-CH3), -0.19(d, 6H, Si-CH3)
Compound 4d: 1 H- NMR (300MHz, CDCl3, 25 0 C): δ 7.53(d, 2H, C9H6), 7.33 (d, 2H, C9H6), 7.26(t, 2H, C9H6), 7.21(t, 2H, C9H6), 7.14(s, 4H, C6H4), 6.27(s, 2H, C9H6), 3.92(s, 4H, CH2), 3.47(s, 2H, C9H6), 1.14(s, 18H, t-Bu), 0.86(s, 2H, NH), -0.06(d, 6H, Si-CH3), -0.15(d, 6H, Si-CH3)
2H, C9H6), 7.28(t, 2H, C9H6), 7.22(t, 2H, C9H6), 7.14(s, 4H, C6H4), 6.66(s, 2H, C9H6), 3.57(s, 2H, C9H6), 1.17(s, 18H, t-Bu), 0.68(s, 2H, NH), -0.09(d, 6H, Si-CH3), -0.14(d, 6H, Si-CH3)
Compound 6d: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.59(d, 2H, C9H6), 7.55(d, 2H, C9H6), 7.36(t, 2H, C9H6), 7.28(t, 2H, C9H6), 7.16(s, 4H, C6H4), 6.37(s, 2H, C9H6), 3.68(s, 2H, C9H6), 3.01(m, 4H, CH2), 2.98 (m, 4H, CH2), 1.14(s, 18H, t-Bu), 0.63(s, 2H, NH), -0.06(d, 6H, Si-CH3), -0.12(d, 6H, Si-CH3)
2.2.7 Synthesis of {TiCl 2 [N( t Bu) Si(Me) 2 ]C 9 H 5 } 2 {(CH 2 ) n [(R) 2 C 6 H 2 ] (CH 2 ) n },
Tertra-lithium salt of 1d-6d was synthesized in hexane solvent using the same procedure as those for di-lithium salt The solution of tetra-lithium salt in THF was transferred to solution of TiCl3(THF)3 in THF at –30 o C The color of the solution changed quickly from dark brown or dark green to black After the mixture reacted at room temperature in 3 hours, AgClwas added The silver mirror precipitated while the reaction was going on 1 hour THF was then removed in vacuo for 4 hours The extraction process with toluene gave the red brown solution, removed toluene to get brown residue The red brown product of 2, 3 were purified by extracting one more with hexane, while 1 and 4-6 were purified by extracting with toluene (Yield 40%)
Compound 1: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.70(d, 2H, C9H5), 7.69(d, 2H, C9H5), 7.34(t, 2H, C9H5), 7.23(t, 2H, C9H5), 7.08(s, 2H, C6H2), 6.26(s, 2H, C9H5), 4.42(q, 4H, CH2), 3.08(m, 2H, CH), 1.14(s, 18H, t-Bu), 1.01(d, 12H, CH3), 0.87(s, 6H, Si-CH3), 0.58(s, 6H, Si-CH3)
13C-NMR (300MHz, CDCl3, 25 0 C): δ 138.04(C, C6H2), 137.53(C, C6H2), 135.90(C, C9H5), 135.36(C, C9H5), 134.75(C, C9H5), 129.21(CH, C9H5), 128.86(CH, C9H5), 128.40(CH, C9H5), 128.29(CH, C9H5), 127.46(CH, C9H5), 124.79(2CH, C6H2), 97.47(C, C9H5), 63.48(C, t-Bu), 32.58(CH3, t-Bu), 32.17(CH2), 28.92(CH, i-C3H7), 23.89(CH3, i-C3H7), 3.52(Si-CH3), 1.16(Si-CH3)
Compound 2: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.73(d, 2H, C9H5), 7.59(d, 2H, C9H5), 7.38(t, 2H, C9H5), 7.25(t, 2H, C9H5), 6.85(s, 2H, C6H2), 6.28(s, 2H, C9H5), 4.37(q, 4H, CH2), 2.48(t, 4H, CH2), 1.47(m, 4H, CH2), 1.35(s, 18H, t-Bu), 1.15(m, 12H, (CH2)3), 0.89(s, 6H, Si-CH3), 0.86(m, 6H, CH3), 0.61(s, 6H, Si-CH3)
13C-NMR (300MHz, CDCl3, 25 0 C): δ 138.70(C, C6H2), 137.46(C, C6H2), 135.89(C, C9H5), 135.74(C, C9H5), 135.53(C, C9H5), 130.94(CH, C9H5), 128.98(CH, C9H5), 128.37(CH, C9H5), 128.16(CH, C9H5), 127.96(CH, C9H5), 124.78(CH, C6H2), 97.60(C, C9H5), 63.52(C, t-Bu), 32.64(CH3, t-Bu), 31.91(CH2), 30.99(CH2, n-C6H13), 29.37((CH2)3, n-C6H13), 22.83(CH2, n-C6H13), 14.36(CH3, n-C6H13), 3.59(Si-CH3), 1.24(Si-CH3)
Anal Found: C: 60.34 %, N: 2.78 %, H: 7.31 % Calculate: C: 60.37 %, N: 2.82 %, H: 7.29%, Compound 3: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.71(d, 2H, C9H5), 7.58(d, 2H, C9H5), 7.34(t, 2H, C9H5), 7.25(t, 2H, C9H5), 6.85(s, 2H, C6H2), 6.28(s, 2H, C9H5), 4.36(q, 4H, CH2), 2.46(t, 4H, CH2), 1.33 (m, 4H, CH2), 1.34(s, 18H, t-Bu), 1.14(m, 20H, (CH2)5), 0.87(s, 6H, Si-CH3), 0.85(m, 6H, CH3), 0.59(s, 6H, Si-CH3)
13C-NMR (300MHz, CDCl3, 25 0 C): δ 138.71(C, C6H2), 137.44(C, C6H2), 135.72(C, C9H5), 135.52(C, C9H5), 135.50(C, C9H5), 130.96(CH, C9H5), 128.96(CH, C9H5), 128.37(CH, C9H5), 128.34(CH, C9H5), 128.15(CH, C9H5), 124.76(CH, C6H2), 97.58(C, C9H5), 63.51(C, t-Bu), 32.63(CH3, t-Bu), 32.12(CH2), 31.05(CH2, n-C8H17), 29.67((CH2)5, n-C8H17), 22.88(CH2, n-C8H17), 14.36(CH3, n-C8H17), 3.58(Si-CH3), 1.25(Si-CH3)
Compound 4: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.71(d, 2H, C9H5), 7.58(d, 2H, C9H5), 7.38(t, 2H, C9H5), 7.28(t, 2H, C9H5), 7.10(s, 4H, C6H4), 6.35(s, 2H, C9H5), 4.35(q, 4H, CH2), 1.35(s, 18H, t-Bu), 0.86(s, 6H, Si-CH3), 0.63(s, 6H, Si-CH3)
13C-NMR (300MHz, CDCl3, 25 0 C): δ 138.00(C, C6H4), 136.38(C, C9H5), 135.92(C, C9H5), 135.18(C, C9H5), 129.19(CH, C9H5), 128.90(CH, C9H5), 128.58(CH, C9H5), 128.38(CH, C9H5), 127.64(CH, C9H5), 124.66(CH, C6H4), 97.43(C, C9H5), 63.48(C, t-Bu), 34.80(CH2), 32.54(CH3, t-Bu), 3.52(Si-CH3), 1.22(Si-CH3)
Compound 5: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.75(d, 2H, C9H5), 7.70(d, 2H, C9H5), 7.41(t, 2H, C9H5), 7.30(t, 2H, C9H5), 7.17(s, 4H, C6H4), 6.57(s, 2H, C9H5), 1.34(s, 18H, t-Bu), 0.89(s, 6H, Si-CH3), 0.66(s, 6H, Si-CH3)
13C-NMR (300MHz, CDCl3, 25 0 C): δ 137.99(C, C9H5), 136.07(C, C9H5), 134.87(C, C9H5), 129.22(CH, C9H5), 128.86(CH, C9H5), 128.65(CH, C9H5), 127.53(CH, C9H5), 126.42(CH, C9H5), 120.06(CH, C6H4), 98.52(C, C9H5), 63.44(C, t-Bu), 32.34(CH3, t-Bu), 3.56(Si-CH3), 1.13(Si-CH3)
Compound 6: 1 H-NMR (300MHz, CDCl3, 25 0 C): δ 7.74(d, 2H, C9H5), 7.57(d, 2H, C9H5), 7.41(t, 2H, C9H5), 7.31(t, 2H, C9H5), 7.08(s, 4H, C6H4), 6.30(s, 2H, C9H5), 3.33(m, 4H, CH2), 3.03 (m, 4H, CH2), 1.36(s, 18H, t-Bu), 0.92(s, 6H, Si-CH3), 0.66(s, 6H, Si-CH3)
13C-NMR (300MHz, CDCl3, 25 0 C): δ 138.92(C, C6H4), 137.41(C, C9H5), 135.77(C, C9H5), 135.00(C, C9H5), 129.06(CH, C9H5), 128.64(CH, C9H5), 128.26(CH, C9H5), 127.91(CH, C9H5), 127.41(CH, C9H5), 124.43(CH, C6H4), 96.83(C, C9H5), 63.11(C, t-Bu), 35.67(CH2), 32.23(CH3, t-Bu), 31.37(CH2), 3.42(Si-CH3), 1.11(Si-CH3).
S UMMARY
The new DCGCs, whose structure consists of three parts: xylene bridge with or without the alkyl branches connecting the two CGCs, electron donor part providing the stable of active site, and the metallic active center, were successfully obtained
As described in details, each of synthetic ligands, b-d, has been manufactured and confirmed structure by nuclear magnetic resonance analysis It is difficult to get the 100% yield of all reactions, however, all steps have almost reacted over 98%
Because of different structures, their solubility differs, and the solvent for extracting should be chosen carefully While ligand 2b and 3b were well soluble in hexane, ligand 1b, 4b-6b dissolving in hexane gave yield only 55% and yield more than 98% within ether In the other hand, the yield of the starting ligands 1a – 3a at the first step is pretty low because the purification of this compound is complex
We have to remove all the starting materials, artifacts, side product and other similar physical and chemical characteristics by work-up process, distillation (if necessary), chromatography, and crystallization Separation and purification methods will be difficult in next reaction if the products were not purified completely Dilitium salt and tetralithium salt compound which are the most important to perform the quality of silane compound and catalyst compound, respectively should be treated with the most possible purification Confirmation of the compounds generated by NMR analysis was easy to find, therefore, it is said that the ligand reaction carried out completely with over 98% yield
The metallocene reaction is the most important to connect the metal part to the compound Experimental results of the tetralitium salt of ligands and TiCl3 (THF)3 reaction show that it is not so complicated and is applicable to various kinds of dinuclear CGC After the reaction conducted in THF solvent, the first extraction was carried out with the toluene, using as the strong solvent to pull out the metal
To assure the purity of catalyst, the hexane or toluene was used to separate the residue These catalysts are very sensitive to oxygen and moisture They are easy contaminated or decomposed in air exposure Because of this reason, metallation eventually yield was 40% The true catalyst structures and composition were also determined by 1 H-NMR, 13 C-NMR and the elemental analysis.
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CHAPTER 3 Polymerization of Isobutyl Vinyl Ether Catalysed by Dinuclear Half-Titanocenes
I NTRODUCTION
Since 1980, metallocene complexes can be activated by methylaluminoxane (MAO) cocatalyst and used as organometallic catalyst to polymerize α-olefin [1−4]
Metallocene polymerization system has been improved remarkably for the last 20 years because of its superior controllability of molecular parameters of polymer
However, it turned out that metallocene systems were not able to be employed to polymerize polar vinyl monomers containing electron donor atom such as nitrogen and oxygen since those atoms may coordinate with the active site to block monomer coordination Poly(vinyl ethers), which were first made in Germany before 1940, have been widely used in adhesive industry [5] Poly(isobutyl vinyl ether) (PIBVE), one of the most useful poly(vinyl ethers), has found the first economically important application as adhesives, impregnating agents for textile, paper, leather whilst the latter has found use in surface coatings [6,7] It is well known that the polymerization of IBVE can be readily accomplished with cationic initiators to produce polymer by addition polymerization mechanisms A variety of initiators such as HCl/SnCl4/nBu4NCl, [8] p-methoxystyrene in aqueous media with
Yb(OSO2CF3)3, [9] aromatic acetals/MtX n , [10] AlCl3/LiAlH4, [11] and IBVE-HCl adduct/TiCl2{OC6H4 i-Pr2(2,6-)}2 [12] have been reported as catalyst systems with better control on molecular weight as well as on tacticity to form isotacticity rich PIBVE Generally, the development of polymerization route to produce polymers with high stereoregularity, high molecular weight (Mn), and narrow molecular weight distribution (PDI) has always been a challenging job in the polymer synthetic area In many cases, extreme reaction conditions may be employed in order to do it, for example, the very low reaction temperature (–78 0 C) must be applied to get isotactic PIBVE with a high meso dyad contents (m = 90–92% ) [11]
Recently a few reports to prepare PIBVE by using metallocene catalyst have also been published Baird and coworkers polymerized vinyl ethers with Cp * TiMe3/B(C6F5)3 [13] (where Cp * is η 5 -pentamethylcyclopentadienyl) via carbocationic mechanism at –78 0 C to obtain polymers with high molecular weight (4.10 4 −10 5 ), narrow molecular weight distribution (PDI = 1.7−2.4) and syndiotactic fraction of 33%–56% Shaffer and Ashbaugh were able to make PIBVE with Cp2 *ZrMe2 and Cp2HfMe2 [14] However, their polymers suffered from the low Mn (3800−28300) and high PDI (4.02−8.8) In 2005, Cadenas-Pliego group published the formation of PIBVE having a high Mn of 94900 and low PDI of 1.79 but low syndiotacticity (r = 36%) with IndTiCl3 catalyst system (where Ind is indenyl) at –78 0 C [15]
Recently, dinuclear half-titanocene compounds which contain two mechanically linked metallocene units have been known to be able to be employed efficiently as a new type of metallocene catalyst to control the stereoregularity, molecular weight and molecular weight distribution of syndiotactic polystyrene [16] We would like to describe the first application of dinuclear half-titanocene to polymerize IBVE to figure out not only the difference between mononuclear and dinuclear catalyst but also the effects of the bridging ligand structure in controlling molecular weight and syndiotacticity Moreover, the effect of aryloxide substitution at titanium on the catalytic properties in polymerization was investigated.
E XPERIMENTAL
IBVE was obtained from Aldrich and distilled over CaH2 before use MAO was purchased from Akzo, USA and used without further purification Methylene chloride (CH2Cl2) was distilled from CaH2 prior to use Cyclopentadienyl titanium trichloride (CpTiCl3) was purchased from Aldrich and used without further purification Catalysts 2, 3, 4, and 5 were synthesized in the laboratory according to reported methods [17-19]
The polymerization was carried out under a dry, oxygen-free atmosphere using standard Schlenk techniques with a double manifold vacuum line Nitrogen gas was purified by passing through a column of molecular sieve (4Å) and Drierite (8 mesh) before use Firstly, CH2Cl2 solution containing the calculated quantity of catalyst was added to the Schlenk flask through degassed syringe The resulting flask was introduced to the polymerization temperature followed by the addition of the designed amount of MAO solution After the activation of the catalyst system for 5 minutes, IBVE was injected to start the polymerization After the designed reaction time, the polymerization was stopped by methanol/HCl 10% solution The formed polymer was precipitated in methanol to be separated by filtration followed by drying under reduced pressure
Mn and PDI were measured by gel permeation chromatography (GPC) using Waters columns (styragel, HR5E) equipped with a Waters 515 pump and a Waters
2410 differential refractometer using diphenyl ether as an internal standard
Tetrahydrofuran (THF) was used as an eluent at a flow rate of 1ml/min Linear polystyrene standards (1.31×10 3 g/mol – 3.58×10 6 g/mol) were used for calibration
The stereoregularity of the generated polymers was determined by 13 C-NMR spectra They were recorded on a Bruker DPX-300 FT-NMR spectrometer in CDCl3 at 50 0 C.
R ESULTS AND DISCUSSIONS
In reality, the dinuclear half-metallocene with polymethylene bridge systems displayed not only the distinguished characters from the well-defined mononuclear metallocenes, but also a strong influence of the nature of the bridging ligand on the syndiospecific styrene polymerization [20] As reported, a variety of half-titanocenes containing aryloxy group showed remarkable catalytic activities for ethylene copolymerization and syndiospecific styrene polymerization [21, 22] Four different dinuclear half-titanocenes (Scheme 3.1) along with CpTiCl3 , 1, were investigated for the polymerization of IBVE to study the relation of catalyst structure to the polymerization behavior
Scheme 3.1 Scheme of polymerization of PIBVE and structure of the catalysts 1 to 5
The results of IBVE polymerization by use of dinuclear half-titanocenes at –10 0 C
Table 3.1 Results of IBVE polymerization by use of dinuclear half-titanocenes at –10 0 C
Catalyst Time (h) Conversion (%) Activity a Mn 10 -4 PDI
Reaction condition: [IBVE]/[catalyst]/[MAO]= 8000:1:100 a kg PIBVE/ mol of catalyst h
Table 3.2 Results of IBVE polymerization by use of dinuclear half-titanocenes at –30 0 C
Catalyst Time (h) Conversion (%) Activity a Mn 10 -4 PDI
Reaction condition: [IBVE]/[catalyst]/[MAO]= 8000:1:100 a kg PIBVE/ mol of catalyst h
It was found that the catalytic behaviors of dinuclear half-titanocenes depended on both the structure of catalyst and the polymerization temperature To easily discuss results, conversion vs time for polymerization of IBVE using five catalysts at –10 0 C and –30 0 C were described in Figure 3.1 and Figure 3.2, respectively
Figure 3.1 Correlation of conversion vs the polymerization time with the catalysts 1 to 5 at –10 0 C
Figure 3.2 Correlation of conversion with the polymerization time with the catalysts 1 to 5 at –30 0 C
It is very interesting that there was a very intimate relation between the catalytic activity and the length of the bridging ligand of the dinuclear half-titanocene The mononuclear catalyst 1 and dinuclear catalysts 2 and 4 which contain three methylenes as a bridge exhibited similarly high activity On the contrary, the catalysts 3 and 5 were found to have much lower activities particularly at the early stage of the polymerization At –30 0 C, the influence of polymerization temperature on the activity of the catalyst was able to be exerted more clearly probably due to the reduced mobility of dinuclear active sites Initiation of polymerization at –30 0 C was slowed down according to the catalyst in the order of 1 < 2 < 4 < 3 < 5 This may reflect that the presence of bridge at dinuclear half-titanocene contribute to play a crucial role to delay the initiation step of the reaction at low temperature
Consequently, it is not unreasonable to suggest that the length of bridging unit have an effect on the reaction which is actually consistent with the observed results [23]
The feature concerned with the catalytic activity was the manifested difference among mononuclear half-titanocene and dinuclear half-titanocenes with trimethylene and hexamethylene bridges The adoption of methylene linkage at dinuclear metallocene would be a positive factor to stabilize the electron deficient active site electronically However, the steric disturbance due to the interaction by the sway movement of polymethylene between two active sites may cause a more difficult coordination of monomer to the cationic species Now the question is why the dinuclear catalysts with six methylenes exhibited such a low activity comparing to the corresponding those with three methylenes It is understandable that trimethylene linkage is so short that it may be hard to cause a significant interaction between the two sides On the other hand, hexamethylene is sufficiently flexible to draw a close contact of two active centers via the formation of six-membered ring intermediate (Scheme 3.2) This kind of process would be able to provide each other not only the opportunity to transfer electronic information of the cationic active site but also the perturbation to make a contact between two sides to lead to reduce a monomer coordination probability It is suggested that these effects should contribute to slow down the propagation rate
Scheme 3.2 Intramolecular interaction between two metal centers in dinuclear half-titanocenes
In addition, another important factor related to the sluggishness of dinuclear half-titanocenes is the property of substituent at titanium center The diisopropyl
+TiL 3 Weak interaction phenoxy group is known as a π electron donor to stabilize the electron deficient active species In terms of steric point of view, 2,6-diisopropyl aryloxy group is bulky enough to give a negative effect on monomer coordination at the metal center
The experiment outcomes that the catalysts with aryloxy group exhibited slower polymerization rate than those with chloride displayed the steric environment around the active site is actually more influential factor to determine the polymerization behavior of the dinuclear catalysts
Finally, the relation between the activity of dinuclear half-titanocenes and polymerization temperature was able to be represented clearly in Figure 3.3 when the IBVE monomer was polymerized at 25 0 C, –10 0 C and –30 0 C with the catalyst 2, [(C5H4)2(CH2)3][(TiCl3)2], and in the presence of MAO in methylene chloride solvent General tendency was observed between the activity of catalysts and the polymerization temperature At 25 0 C, the monomer has been polymerized most quickly among three temperatures Monomer solution became very sticky just after 1 hour of polymerization, whereas at –10 0 C and –30 0 C polymers could not be collected up to three or four hours of reaction
Figure 3.3 Effect of temperature on conversion of IBVE polymerization vs time using dinuclear half-titanocene catalyst 2
The variation of molecular weight and molecular weight distribution of PIBVE seems to be sensitive to the polymerization conditions as well as the nature of the catalyst It has been noted that the polymerization at higher temperature produced the polymer with the smaller molecular weight (Figure 3.4) It was notable that the molecular weights of the formed polymers at 25 0 C were close to 25,000 regardless of conversion On the other hand, molecular weight values of the polymers generated at –10 0 C and –30 0 C were getting larger according to the increase of conversion from 36,000 to 282,000 It was pointed that narrow PDI’s of the polymers (near 2.0) had been maintained through the whole process of the reaction, which was known as the general trend of single site catalyst polymerization An interesting feature was pointed out from these results about the effect of polymerization temperature on molecular weight of PIBVE The experimental molecular weights at –30 0 C were more closed to the calculated molecular weight than those at –10 0 C The theoretical molecular weight values are calculated by Mn(cal) = ([M]0/2[cat.]0)MMCM, where [M]0 and [cat.]0 are the initial concentrations of the monomer and dinuclear half-titanocene catalyst, respectively;
MM is the molecular weights of monomer and CM is the monomer conversion [8,9] In order to confirm the effects of temperature on the control on molecular weight of polymer the polymerization of IBVE was conducted with all five catalysts in this study It was observed that the molecular weight values of the polymers formed at –30 0 C were fitted better than those formed at –10 0 C on the calculated values as shown in Figure 3.5 and Figure 3.6 In these graphs, the experimental molecular weight values were higher than the theoretical ones until less than 40% of conversion However, as the conversion increases, the molecular weights of polymers become smaller than the calculated ones probably because of the inefficient initiation with the slow growing carbocation and the fast termination at high conversion Meanwhile, PDI of resulting polymer almost did not change during the whole reaction period and the range of value was quite narrow (PDI ≤
2.3) due to the single active site of catalyst
Figure 3.4 Mn and PDI vs conversion for polymerization of IBVE using dinuclear half-titanocene catalyst 2 at three different temperatures
Figure 3.5 Mn and PDI vs conversion for polymerization of IBVE using dinuclear half-titanocene catalysts at –10 0 C
Dependence of molecular weight of PIBVE upon polymerization temperature should be explained by β-H elimination rate of the reaction At high temperature the termination step through β-H elimination would proceed frequently to liberate a constant length of polymer chain as indicated by the experiment However, as the temperature becomes lower, the rate of β-H elimination should be suppressed significantly to lead to a longer chain of polymer molecule The range of termination suppression may be directly related to the activation energy of β-H elimination Our experiment demonstrated very well that β-H elimination may be completely inhibited around the temperature of –30 0 C since almost living character has been observed at this temperature, as shown in Figure 3.6, in which a linear relation of molecular weight with the conversion is well coincided with the line of theoretical polymerization
3 Mn (cal) Mn PDI Mn PDI
Figure 3.6 Mn and PDI vs conversion for polymerization of IBVE using dinuclear half-titanocene catalysts at –30 0 C
Another explanation may be applied that these catalysts also polymerize via both coordination insertion mechanism and cationic mechanism below the change in polymerization temperature This explanation is similar to the case of Baird and coworkers In the first example of polymerization of vinyl ether by metallocene, Baird and coworkers reported that the polymerization of vinyl ethers could be induced by Cp*TiMe3–B(C6F5)3: the polymers were formed via carbocationic initiation by the titanium-containing cationic complex (Cp*TiMe2) + rather than via Ziegler–Natta process [13] Later, some other reports showed that resultant polystyrene possessed both atactic (via carbocationic mechanism) and syndiotactic (via coordination insertion mechanism) stereo regularity with Cp*TiMe3 catalyst under conditional polymerization temperature, beside, the mechanism of polymerization of ethylene and α-olefins was also explored [24-26] In our case, the polymerization happened with coordination insertion mechanism at 25 0 C Chain termination was dominant factor to control molecular weight, and the active species of the polymerization should be cationic at low temperature The cationic complex formed by methylation of metal by MAO may initiate the polymerization and the propagating cationic end may be stabilized by MAO, preventing termination with the chloride anion
It was found out that the nature of catalyst had effect on the variation of molecular weight of PIBVE as well For example, in order to reach about 120,000g/mol of molecular weight the required conversion has been varied according to the catalyst in the order of 1(63%) > 4(60%) > 2(25%) > 5(20%) > 3(15%) at –10 0 C, which may be considered as the correlation of catalyst character with the molecular weight of the produced polymer This result proposes that two factors seem to act as an important role to determine the molecular weight of the polymer The first one is the effect of the bridging ligand of the dinuclear half-titanocene The dinuclear catalysts formed a longer polymer chain than CpTiCl3 Among dinuclear catalysts the hexamethylene bridged catalysts 3 and 5 were able to form higher molecular weight polymer than the trimethylene bridged ones 2 and 4, which indicated that the six methylene bridge is more influential to generate a longer chain An extremely interesting outcome has been found from the change of chloride to aryloxy group For instance, the catalyst 3 containing not only hexamethylene bridge but also trichlorides at titanium was found to form the highest molecular weight polymer However, catalyst 5 having hexamethylene bridge with aryloxy group was observed to form the polymers with lower molecular weight This result represents clearly that the substituent effect at the titanium center exerted a less significant influence than the bridge nature to control molecular weight of the polymers This result showed that the higher activity catalysts were good to make a shorter PIBVE, which is a general tendency in metallocene polymerization
Since stereoregulation in vinyl ether polymerization is an issue of great importance, many researchers have attempted to control the stereoregularity of PIBVE by desired catalyst design [10-12] In recent years, dinuclear half-titanocene has been successfully employed for the preparation of highly syndiotactic polystyrene [16-19]
Substituent effect of half-titanocene on structure of polymer has been demonstrated very well by Nomura [21] Even if the isobutyl ether does not have the steric bulk as the phenyl group in styrene monomer, the dinuclear catalysts with the rich-electron property of –OR group may have a positive effect on the control of syndiotacticity of PIBVE Figure 3.7 displays 13 C-NMR spectra of samples obtained by the catalyst 1, 2, 3, 4 and 5 at –30 0 C The dyad distribution of PIBVE can be determined from the peak intensity ratios of the main chain methylene carbons [-CH2-CH(OiBu)-] around 39–42 ppm where the meso (m) and racemic (r) dyads are well resolved
The result showed that the syndiotactic fraction of PIBVE with five catalysts was arranged in the order of 1 < 2 < 3 < 4 < 5 It is remarkable that the tendency of stereoregularity is pretty different from not only that of activity of the catalyst but also that of molecular weight of polymer In terms of the catalyst structure there are two factors to adjust polymerization scheme, which are the effect of bridge and substituent The mononuclear, normal catalyst 1 was turned out to prepare PIBVE with the lowest syndiotactic diad of 45% Two catalysts 2 and 3 with trichlorides as an anionic ligand formed the polymer with 47% and 49% of syndiotacticity, respectively
Figure 3.7 13 C-NMR spectrum of PIBVE using catalyst 1, 2, 3, 4, 5 systems in
C ONCLUSIONS
Four different dinuclear half-titanocenes (Figure 3.1) along with CpTiCl3 were investigated for the polymerization of IBVE to study the relation of catalyst structure to the polymerization behavior It was found that the polymerization behaviors of dinuclear catalysts were dependent on both the structure of catalyst and the polymerization temperature The mononuclear catalyst 1 and dinuclear catalysts 2 and 4 which contain three methylenes as a bridge exhibited similarly high activity In contrast, the catalysts 3 and 5 were found to have much lower activities particularly at the early stage of the polymerization The steric disturbance due to the interaction by the sway movement of polymethylene between two active sites may be attributed to control the activity of the dinuclear catalysts The variation of molecular weight and molecular weight distribution of PIBVE seems to be sensitive to the polymerization conditions as well as the nature of the catalyst It was pointed that narrow PDI’s of the polymers (near 2.0) had been maintained through the whole process of the reaction, which was known as the general trend of single site catalyst polymerization The experimental molecular weights at –30 0 C were more closed to the calculated molecular weight than those at –10 0 C Dependence of molecular weight of PIBVE upon polymerization temperature should be explained by β-H elimination rate of the reaction At high temperature the termination step through β-H elimination would proceed frequently to liberate a constant length of polymer chain as indicated by the experiment
However, as the temperature becomes lower, the rate of β-H elimination should be suppressed significantly to lead to make a longer chain of polymer molecule
Among dinuclear catalysts, the hexamethylene bridged catalysts 3 and 5 were able to form higher molecular weight polymer than the trimethylene bridged ones (2 and
4) The polymerization showed that the syndiotactic fraction of PIBVE with five catalysts was arranged in the order of 1 < 2 < 3 < 4 < 5 It turned out that the dinuclear half-titanocenes are able to make slightly higher syndiotactic PIBVE than
CpTiCl3 It is noteworthy that the catalysts 5 and 4 with aryloxy group at titanium prepared greater stereoregularity than the catalysts 3 and 2 with chloride group
This result indicates that the aryloxy substitution at titanium affected more powerfully on stereochemical control of the polymerization than the length of bridge at the dinuclear half-titanocene This study suggests if the well and intentionally designed dinuclear catalyst could be prepared on the basis of the reported knowledge the stereochemical control of PIBVE should be established by the metallocene polymerization system.
ETHYLENE/STYRENE COPOLYMERIZATION USING NEW DCGC
I NTRODUCTION
The constrained geometry catalysts with the short bridge between the Cp * ligand and amido donor which force the open nature of the catalysts’ active site was found to be an extremely efficient catalyst for copolymerization of ethylene and styrene as well as linear α-olefins Depending on the styrene content, ethylene–styrene interpolymer (ESI, developed by Dow Chemicals) range from semi-crystalline to amorphous materials which are effective blend compatibilizers for PS/PE blend and have also potential in foam, films and sheet applications [1] The requirements for a successful ethylene/styrene copolymerization catalyst are severe and include high activity, high comonomer incorporation, ability to generate high molecular weights, and ability to operate at the high temperatures, compatible with most commercial polymerization processes [2] Indeed, beside low activity, heterogeneous Ziegler-Natta catalysts only incorporate very small amounts of styrene [3] Although CGC afforded poly(ethylene-co-styrene) exclusively, but styrene head-to-tail repeat units were not observed and synthesis of the copolymer with high styrene contents was thus seemed difficult [4,5] In 2004, Marks demonstrated dinuclear constrained geometry catalysts that exhibit much better styrene incorporation (up to 76%) [6] In addition, our group reported that dinuclear CGC systems containing different polymethylene length bridge were more effective to improve polymerization activity and incorporate styrene in the polyethylene backbone [7,8] However, the application of the rigid xylene bridge properties on DCGC has not been studied yet
In Chapter 2, we have already designed and synthesized novel DCGC structures
The ethylene/styrene copolymerization have been tried with six new structures complexes 1, 2, 3, 4, 5, 6 and Dow CGC in order to understand the influence of bridges on the catalyst behaviors The results of ethylene/styrene copolymerization will be presented and discussed in this chapter.
E XPERIMENTAL PROCEDURES
All experiments were performed under dry nitrogen, in a drybox or using standard Schlenk line techniques Toluene was distilled from sodium/benzophenone ketyl prior to use MMAO (5.9wt% Al, Akzo, USA) was used without further purification Ethylene (Matheson, polymerization grade) was purified by passage through a supported MnO oxygen-removal column and an activated Davison 4 Å molecular sieve column Styrene (Aldrich) was dried over CaH2 and vacuum-transferred into storage tubes
Ethylene/styrene copolymerization was carried out in the dry 300-ml glass reactor, sealed with a rubber septum and cycled two times between vacuum and nitrogen to remove oxygen After evacuation of the nitrogen, the reactor was saturated with continuous flow of ethylene at atmospheric pressure (1.0 atm) and reaction temperature Then, a proper amount of toluene and MMAO were injected to the flask The reacting medium was stirred for 30 min in order to dissolve the ethylene and to homogenize the medium After that, the calculated amount of styrene was introduced into the reactor The polymerization was initiated by injection of the prepared catalyst solution in toluene After a measured time interval, the polymerization was quenched by the addition of acidified methanol containing 10% HCl Polymer was collected by filtration, washed with excess methanol, and dried under vacuum overnight to a constant weight
Ethylene concentration in toluene was calculated according to Henry’s law:
C Ethylene Ethylene 0 L where CEthylene = ethylene concentration (mol×L -1 ); PEthylene = ethylene pressure (atm); H0 = Henry coefficient = 0.00175 mol ×L -1 ×atm -1 ; ΔHL = enthalpy of solvatation of ethylene in toluene = 2569 cal×mol -1 ; R = 1.989 cal×mol -1 ×K -1
1H-NMR and 13 C-NMR assays of polymer were conducted in 1,1,2,2-tetrachloroethane-d2 at 110 0 C Differential scanning calorimetric (DSC) data was carried out with Pyris Diamond DSC under nitrogen atmosphere [conditions: heating from 20 to 300 0 C (10 0 C/min), cooling from 300 to 20 0 C (10 0 C/min)] The second heating cycle was used for collecting DSC thermogram data at a ramping rate of 10 0 C/min The viscosity averaged molecular weight (Mη) of polymer was measured in decahydronaphthalene at 135 0 C by a modified Ubbelohde-type viscometer according to ASTM-4020 Molecular weight (Mw) and molecular weight distribution (MWD) were measured by Polymer Laboratory PL-GPC220 at 170 0 C in 1,2,4-trichorobenzene(TCB) A calibration curve was established with narrow molecular weight distribution polystyrene standards.
R ESULTS AND DISCUSSIONS
The goal of this study is to investigate the influence of structural feature of the bridging ligand in dinuclear metallocene to catalytic properties Indeed, the effects of variety of branches in DCGC complexes 1-4 and xylene bridge length (without or multi methylene group) in DCGC 5-6, which were designed in chapter 2, were studied in the copolymerization of ethylene and styrene All polymerizations were conducted at the following general conditions: [cat] = 20μmol, [MMAO] / [cat] 2000, t = 2 h and 100ml toluene to compare the effectiveness of this project with our previous reported polymerization results using polymethylene bridge DCGC
According to some other reports, such as Marks [6,9] , Sernetz [4] , Wu [10] the styrene unit content of the polymerization products as well as catalytic activities was affected by increasing styrene concentration in feed In our laboratory conditions, the copolymerizations of ethylene and styrene were performed with a constant pressure of ethylene, 1 atm, at two concentrations of styrene, 0.4 mol/l and 1.3 mol/l, to change the feed composition In addition, the polymerizations with all catalysts were studied at two temperatures of 40 0 C and 70 0 C Mononuclear Dow CGC, the most currently popular CGC catalyst, was used to polymerize at the same condition with our new catalyst to consider the effectiveness of our catalysts The results of catalytic activity, styrene content, molecular weight and microstructure of polymer will be shown in this chapter
4.3.1 Effect of catalyst structure on catalytic activity
The activity results at 40 0 C and 70 0 C are shown in Table 4.1 and Table 4.2, respectively
Table 4.1 The catalytic activity results obtained at various styrene concentrations at 40 0 C
Run Catalyst Tp ( 0 C) [styrene] a [S]/[E] b Activity c
14 Dow 40 0.4 3.7 190.6 a styrene concentration (mol/l) b monomer feed ratio (mol/mol) c activity (kg mol -1 h -1 atm -1 )
Table 4.2 The catalytic activity results obtained at various styrene concentrations at 70 0 C
Run Catalyst Tp ( 0 C) [styrene] a [S]/[E] b Activity c
28 Dow 70 0.4 5.3 240.5 a styrene concentration (mol/l) b monomer feed ratio (mol/mol) c activity (kg mol -1 h -1 atm -1 )
The polymerizations exhibit higher catalytic activity with increasing temperature and the initial monomer ratio of [S] / [E] Especially, the activity values at two conditions [S]/[E] = 5.3, Tp = 70 0 C and [S]/[E] = 12, Tp = 40 0 C are similar This suggests that the active species promoting the copolymerization results from a reaction requiring high temperatures As shown in the Table 4.1 and Table 4.2, the tendency of activity has been maintained throughout ethylene–styrene copolymerization in the order 6 > 4 > 3 > 2 > 1 > 5 It means that in the first type of catalyst with different branches on the bridge, the longer branch, the greater activity, however without branch had highest activity It can be explained by the difference of steric and electronic characteristics between bridge with and without branches, and between iso-propyl branch and n-hexyl, n-octyl branch as the expected structure (Scheme 4.1) First, the steric hindrance of branch may reduce the monomer coordination and insertion which led to lower catalytic activity of the branched xylene bridge DCGC Second, the alkyl branch may reach out the titanium active site to donate electron to the metal center for high catalytic activity
However, the activity of without branch catalyst 4 is higher than catalyst 1, 2, 3 due to the steric effect may be stronger than electronic effect On the other hand, the characteristic substituent, n-hexyl and n-octyl of catalyst 2 and catalyst 3 have similar steric structure as well as electrical properties Both of them are longer, more flexible, more easily movable or curly and higher electron donating than isopropyl group with two methyl group rotating around the methine carbon For these reasons, the activities of catalyst were little decreasing 3 > 2 > 1
Interaction between Active site and Branch at phenyl ring
Scheme 4.1 Intramolecular interaction between branch and active centers
In the second type of bridge with different number of methylene group, the decreasing activity is in the order 6 > 4 >> 5, which illustrated that the dinuclear catalysts with more [CH2] units as a bridge represented greater activity The present result may be attributed to steric effects, according to bulky aromatic group of styrene Concerning the effect of steric congestion around the metal center on activity, it is known that steric hindrance prevents facile access to the coordination site to slow down the propagation rate On this basis, it is not so surprising to anticipate that the dinuclear metallocene with a shorter bridging ligand experienced more steric disturbance than the one with a longer bridging ligand As can be seen from the experimental data, this anticipation agrees with the observed results [8]
Complexes 6 and 4 with a longer bridge displayed so much higher catalytic activity compared to the catalysts 5
Compare with Dow CGC, almost our catalysts had greater activity than Dow CGC, except for catalyst 1 in case of 1.3mol/l styrene in feed and catalyst 5 And the catalytic activities of new catalyst system except catalyst 5 had higher value than polymethylene bridge system because the rigidity of the phenyl ring limited the free movement of the two metal centers, which disfavored a close contact between the two metal atoms; in hence the bimolecular deactivation of active centers was effectively suppressed In summary, the general catalytic activity decreased in the order of 6 > 4 > 3 > 2 > 1 ≈ Dow > 5
4.3.2 Effect of catalyst structure on styrene content
The typical 1 H-NMR spectra of ethylene-styrene copolymer at 110 0 C using 1,1,2,2-tetrachloroethane-d2 solvent is depicted in Figure 4.1 The solvent 1,1,2,2-tetrachloroethane-d2 was used as the deuterated solvent because its NMR spectra features do not overlap with any of the polymer resonances The styrene contents were calculated based on the integral of the aromatic region (Aaromatic) and the aliphatic region (Aaliphatic) according to this equations: S% = 4Aaromatic / (Aaromatic
+ 5Aaliphatic) [9] The styrene content measurement by 1 H-NMR spectrum were summarized in Table 4.3 and 4.4
Figure 4.1 1 H-NMR spectra of typical E/S copolymer sample (Run 8)
It is found that the dinuclear catalysts mentioned in this study are very efficient to incorporate styrene in the polyethylene backbone The results show that the styrene contents of products correspond to the increase in the [S]/[E] ratio in feed, up to 33.4% Comparing six catalysts at 70 0 C and styrene concentration 1.3 mol/l, these catalysts gave a similar amount of styrene content, about 32.5%, except catalyst 5
However, at lower [S]/[E] ratio, we can see the dependence of styrene content on the catalyst structures, which give the variation of the styrene content in ascending order as follow: catalyst 5 ≤ Dow < 4 < 6 < 1 < 2 < 3 Figure 4.2 shows 13 C-NMR spectra (methylene and methane region) of the copolymers prepared by seven catalysts from run 1 to run 7 at 40 0 C, 1.3mol/l styrene The regiospecificity of styrene insertion of our catalyst system seems to be higher than Dow CGC as suggested by the relative appearance of the Sαβ cacbon of tail-to-tail enchainment observed in copolymers The reducing resonance intensities of strong signals at 29.7 ppm of the polyethylene sequences, the increasing of resonance intensities at 27.5, 36.9, and 46.2 ppm (Sβδ, Sαδ, and Tδδ, respectively) of sequences of EESEE
3 2,4 and in addition of peak at 25.3 ppm (Sββ) which represents the SES sequence indicated that all produced polymers had a substantially alternating structure The absence of a signal for Tββ at 41.3 ppm and for Sαα at 43.6 ppm shows that there is no styrene–styrene sequence in the copolymers This demonstrated that the dinuclear CGC in this experiment might be advantageous over the reported catalysts to obtain more randomly distributed poly(ethylene-co-styrene)s This result is distinct from the reported studies [2, 9-12]
The copolymerization products are rubber-like in appearance The melting points (Tm) of the obtained copolymers could not be detected by DSC measurements, no matter how high the comonomer incorporation in the copolymers is The melting point (Tm) is attributed to a unique blocky microstructure which offers enough consecutive sequences of comonomer units in the polymer backbone to form a crystalline phase Therefore, all ethylene/styrene copolymer produced by our catalyst were amorphous
Table 4.3 The styrene content results obtained at various styrene concentrations at 40 0 C
Run Catalyst Tp ( 0 C) [styrene] a [S]/[E] b Styrene content in copolymer (%)
14 Dow 40 0.42 3.7 9.5 a 1-styrene concentration (mol/l) b monomer feed ratio (mol/mol)
Table 4.4 The styrene content results obtained at various styrene concentrations at 70 0 C
Run Catalyst Tp ( 0 C) [styrene] a [S]/[E] b Styrene content in copolymer (%)
28 Dow 70 0.42 5.3 10.4 a styrene concentration (mol/l) b monomer feed ratio (mol/mol)
Figure 4.2 13 C-NMR spectra of ethylene-styrene copolymer samples from run 1-7
4.3.3 Effect of catalyst structure on molecular weight
The molecular weight results are shown in Table 4.5 and Table 4.6
Table 4.5 Molecular weight of ethylene/styrene copolymers at 40 0 C
Run Catalyst Tp ( 0 C) [styrene] a [S]/[E] b Mη 10 -4 Mw 10 -4 MWD
14 Dow 40 0.4 3.7 7.40 - - a styrene concentration (mol/l) b monomer feed ratio (mol/mol)
Table 4.6 Molecular weight of ethylene/styrene copolymers at 70 0 C
Run Catalyst Tp ( 0 C) [styrene] a [S]/[E] b Mη 10 -4 Mw 10 -4 MWD
28 Dow 70 0.4 5.3 4.26 4.34 2.39 a styrene concentration (mol/l) b monomer feed ratio (mol/mol)
The basis for molecular weight determination techniques is the measurement of the size of random coils in very dilute solution As widely known, Gel Permeation Chromatography (GPC) can determine the molecular weight and molecular weight distribution by separating the molecules according to their random coil dimensions and supposing that molecules in solution adopt random coil configuration with hydrodynamic volumes that increase as a predictable function of their molecular weight The ability application of GPC is strongly depending upon the range of pore sizes In our GPC condition, maybe the range of pore sizes of GPC were not appropriate to sample sizes, GPC cannot work with some copolymer samples So, I tried to check the average viscosity molecular weight The results displayed that the reducing of molecular weight upon the increasing the [S]/[E] ratio as well as polymerization temperature follows the general tendency For example, the viscosity molecular weights of polymers using catalyst 1 decrease from 1,520,000 to 60,400 where increasing [S]/[E] ratio from 3.7 to 12 This indicates that improvement of styrene content in polymer accompanies the reduction of molecular weight of the formed polymer The molecular weight seems sensitive to the catalyst structure, different bridge have the different value of molecular weight
The main reason would have more frequencies to proceed β-H elimination to terminate propagation for the delivery of low molecular weight polymer under the influence of steric and electronic of bridge on the active site We designed two types of bridge, so the effect of catalyst structure on molecular weight (Mη, Mw, MWD) will be explained by branches on bridge and length of bridge as following
First, comparison between different branches on xylene bridge, the catalyst 1 provided the highest Mη, and the order was 1 > 4 > 2 > 3 > Dow As mentioned above, among four new catalyst structures, catalyst 2 and 3 with the hexyl and octyl branch have more electron-donating power which promotes the propagation concurrent with termination In case of catalyst 4, the disappearance of branch’s steric effect provides the more open coordination environment of active site which makes the β-hydride elimination reaction to happen easier than catalyst 1
Second, comparison on the length of xylene bridge, the longer bridge the greater molecular weight, catalyst 6 > 4 > 5 As you know, the electron withdrawing effect decreases the electron density around the active species causing an increase of the electrophilic character of the transition metal The higher electrophilic character of the transition metal leads to instability of the active center In catalyst 5, the direct connection of the phenyl bridge to indenyl group caused the unstable of active site, hindered the coordination process, so, the catalyst 5 had lowest activity, styrene incorporation and molecular weight Whereas, the combination of rigid phenyl group and the lively polymethylene group in the bridge can avoid an intramolecular deactivation between active sites and promote the electron-donating nature, which improved the molecular weight of styrene copolymer as well as catalytic activity
C ONCLUSIONS
The copolymerization of ethylene and styrene was investigated using a series of dinuclear CGC with different branches and different bridge’s lengths The results significantly expand the scope of applicable comonomers in dinuclear constrained geometry catalyst The polymerization studies revealed that:
(i) The catalyst activity strongly depended upon the polymerization condition as well as the bridge ligand in designed DCGC All catalysts can be active at high temperature and high [S]/[E] ratio With same length, the activity of structure without branches is better than with branches Among structures with branches, the longer branch produces higher activity than the short ones The structure without branches whose bridge is longer has higher activity
(ii) The molecular weight as well as styrene content of poly(ethylene-co-styrene) produced by the dinuclear CGC are also influenced by the employed catalysts However, with first type, the molecular weight trend is opposite of the styrene content; with second type, the molecular weight increased with the length of bridge 13 C-NMR results show that our DCGCs are very efficient to produce the random ethylene/styrene copolymer with high molecular weight
(iii) Except catalyst 5, activity, styrene content and molecular weight of polymer obtained in this study using other catalysts much better than ones provided by Dow CGC Especially, the molecular weight of these styrene copolymers are dependent on the catalyst structure, but always higher than molecular weight of copolymer produced by dinuclear polymethylene bridge CGC
It turned out that designed structure of catalyst is the key to control the activity, monomer content as well as molecular weight of polymer Our structures are very efficient in copolymerization behavior of styrene.
ETHYLENE/1-HEXENE COPOLYMERIZATION USING NEW DCGC
I NTRODUCTION
Linear low-density polyethylenes (LLDPEs) synthesized by the copolymerization of ethylene and various α-olefins are materials of great commercial significance because they give higher tensile strength, puncture and anti-tear properties, particularly suitable for film applications with better environmental stress cracking as well as chemicals and to ultraviolet radiation resistance [1] Mitsui, Exxon, Dow, and other companies concentrated their efforts on the development of single-site metallocene catalysts, and as a result, a new generation of Short Chain Branched polyethylenes (SCBPEs) was introduced [2-13] CGCs were found to be superior catalysts not only for the production of ethylene and linear α-olefins copolymers but also for incorporation styrene into polyethylene backbone It has thus been believed that design of the efficient transition metal complex catalysts should be the key for the success, and recent progress in the newly designed catalysts offers a new possibility Our group investigated the characteristic family of polymethylene-bridge dinuclear CGC [14-16] using combination of the well-defined mononuclear properties and the nature of the bridging ligand Although a series of dinuclear half-titanocenes with xylene bridge was studied on styrene polymerization in order to figure out the influence of bridge stiffness, geometric arrangement and space orientation of the two active sites on the catalytic property, the DCGC with rigid xylene bridge have not explored until now As described in previous chapters, structure features of DCGC with branched xylene bridge strongly influence the coordination and insertion of styrene in the ethylene copolymerization In addition, an efficient catalyst means that it can perform polymerization or copolymerization with some monomers, especially, in incorporation of linear α-olefins such as 1-hexene into polyethylene at various amounts Thus, the designed dinuclear complexes 1, 2, 3, 4 and Dow CGC were employed for the copolymerization of ethylene and 1-hexene and the results will be presented and discussed in this chapter.
E XPERIMENTAL PROCEDURES
Toluene was distilled from sodium/benzophenone ketyl prior to use MMAO (5.9wt% Al, Akzo, USA) was used without further purification Ethylene (Matheson, polymerization grade) was purified by passage through a supported MnO oxygen-removal column and an activated Davison 4 Å molecular sieve column 1-hexene (Aldrich) was dried over Na and vacuum-transferred into storage tubes
Ethylene/1-hexene copolymerization was carried out in the dry 300-ml glass reactor, sealed with a rubber septum and cycled two times between vacuum and nitrogen to remove oxygen The nitrogen was evacuated and the reactor was saturated under 1.0 atm of continuous flow of ethylene at the reaction temperature
Then, a proper amount of toluene, 1-hexene and MMAO were injected to the flask
The reacting medium was stirred for 30 min in order to dissolve the ethylene and to homogenize the medium The polymerization was initiated by injection of the prepared catalyst solution in toluene After a measured time interval, the polymerization was quenched by the addition of acidified methanol containing 10% HCl Polymer was collected by filtration, washed with excess methanol, and dried under vacuum overnight to a constant weight
Ethylene concentration in toluene was calculated according to Henry’s law:
C Ethylene Ethylene 0 L where CEthylene = ethylene concentration (mol×L -1 ); PEthylene = ethylene pressure (atm); H0 = Henry coefficient = 0.00175 mol ×L -1 ×atm -1 ; ΔHL = enthalpy of solvatation of ethylene in toluene = 2569 cal×mol -1 ; R = 1.989 cal×mol -1 ×K -1
1H-NMR and 13 C-NMR assays of polymer were conducted in C6D6 at 78 0 C
Differential scanning calorimetric (DSC) data was carried out with Pyris Diamond DSC under nitrogen atmosphere [conditions: heating from 20 to 150 0 C (10 0 C/min), cooling from 150 to 20 0 C (10 0 C/min)] The second heating cycle was used for collecting DSC thermogram data at a ramping rate of 10 0 C/min The viscosity averaged molecular weight (Mη) of polymer was measured in decahydronaphthalene at 135 0 C by a modified Ubbelohde-type viscometer according to ASTM-4020 Molecular weight (Mw) and molecular weight distribution (MWD) were measured by Polymer Laboratory PL-GPC220 at 170 0 C in 1,2,4-trichorobenzene(TCB) A calibration curve was established with narrow molecular weight distribution polystyrene standards.
R ESULTS AND DISCUSSIONS
5.3.1 Effect of the polymerization conditions
Because the catalytic behavior is strongly dependent on the polymerization conditions, the effect of the reaction parameters, such as the catalyst concentration, [MMAO]/[catalyst] molar ratio, and polymerization time were studied In addition, the effect of both 1-hexene concentration and polymerization temperature were also examined simultaneously with the influence of catalyst structures on the stability of active center and the copolymerizability a Effect of catalyst concentration and the MMAO – to – catalyst molar ratio on catalytic activity and the viscosity averaged molecular weight (Mη)
Catalyst concentration as well as the MMAO concentration is the key parameter to form the complexes activating the polymerization process These polymerizations using catalyst 2 with 5ml 1-hexene (0.4 mol/l) were carried out in 100ml toluene at 40 0 C in 1 hour The results are show in Table 5.1
Table 5.1 Correlation of catalytic activity with concentration of catalyst [Al]/[Ti] [Ti] àmol/L Activity a Mη (x10 -4 )
2000 20 134 3.3 a activity(kg polymer.mol -1 h -1 atm -1 )Results show that the catalytic activities under the test condition increase linearly with increasing catalyst concentration and [MMAO]/[cat]@00, which might be explained by a large amount number of activated metal species However, the molecular weight (Mη) of polymers decreases with increasing catalyst concentration One possible explanation is that the chance of chain transfer process was caused by an excess of MMAO at high catalyst concentration It was also easy to understand that the catalytic activity decrease 3 times from 422 to 134 when decreasing the ratio of MMAO to catalyst 2 times and [cat] = 20àmol/l, while the molecular weight lightly goes up from 31,000 to 33,000, since a high amount of MMAO is necessary for elimination of all kinds of impurities existing in the polymerization medium and generating the active species Therefore, [catalyst] 20àmol/l and [MMAO]/ [catalyst] = 4000 were used in the following studies b Effect of polymerization time on catalytic activity
Figure 5.1 show that catalyst activity increases with time up to a maximum
(roughly 1 hour) after which a steady decline ensues, due probably to deactivation of catalyst It indicates that the catalytic system we have employed was stable The length of time over which the catalyst was stable is very impressive and important for an industrial application of the system Thus, 1 hour was chosen as the polymerization time for the following researches time (min)
Ac tiv ity [kg p olymer /(mol Ti* hou r)]
Figure 5.1 Correlation of catalytic activity with polymerization time
5.3.2 Effect of the catalyst structure
A major focus of our work has involved the impact of new catalyst structure various branches (long, short and no branch) on the catalytic behavior and properties of polymer such as catalytic activity, the incorporation of 1-hexene, molecular weight and thermal properties The catalyst complexes 1, 2, 3, 4 were examined at the different polymerization temperature and the compositions of monomer in feed, [H]/[E] The temperature is chosen below 50 0 C due to the limit of the boiling point of 1-hexene (~61 0 C) and polymerization condition at 1atm of ethylene The mononuclear Dow CGC, the most currently popular of LLDPE catalyst, was used to polymerize at the same condition with our new catalyst to study the effectiveness of our catalysts All following experiments described in the present work were conducted using these conditions: [cat] = 20μmol, [MMAO]/[cat] = 4000, t = 1 h, 100ml toluene a Catalytic activity
The catalytic activity results were shown in Table 5.2 and Table 5.3 The general catalytic activity of these complexes were consistent in the order 4 >> 2 > 3 > 1 >
Dow CGC system at same condition (Table 5.2) It can be seen obviously the effect to catalytic activity of R substituents on the xylene bridge in 1–4 For example, under the same condition at 40 0 C and [H]/[E] = 4, catalyst 4 having a pure xylene ligand substituent show the superior activity, 687 kg.mol -1 h -1 atm -1 , whereas catalyst 2, 3 and 1, containing n-hexyl, n-octyl and isopropyl branch on xylene bridge, respectively, displayed the pretty similar activity 421 > 389 > 386 kg.mol
-1.h -1 atm -1 , and CGC shows 348 kg.mol -1 h -1 atm -1
Table 5.2 Catalytic activity results obtained at various monomer feed ratios [H]/[E] at 40 0 C
15 Dow 40 8 336 a monomer feed ratio (mol/mol) b activity (kg mol -1 h -1 atm -1 )
Table 5.3 Catalytic activity results obtained at various monomer feed ratios [H]/[E] at 50 0 C and 30 0 C
27 4 30 4 463 a monomer feed ratio (mol/mol) b activity (kg mol -1 h -1 atm -1 )
These results might be mainly ascribed to the steric effect of the R group The expected structure shown in Scheme 4.1 described that the branch may reach out the titanium active site So, these blocking active site created by the interaction between alkyl branch and titanium led to suppress monomer coordination to the metal center to lower catalytic activity [17] On the other hand, the characteristic substituent, n-hexyl and n-octyl of catalyst 2 and catalyst 3 have similar steric structure as well as electrical properties Both of them are long, flexible, easily movable or curly branches which can donate electron to the metal center for high catalytic activity For this reason, the activity of catalyst 2 and catalyst 3 is little higher than catalyst 1 The important point of these experimental results of the polymerization activity is that the dinuclear CGC having interaction substituents with the active site also show higher efficient activity than mononuclear Dow CGC
It can be explained by that the nature of the bridges, the rotation of metallocene units around the bridge and a nearly linear structure affect strongly on the activity
In addition, the effect of catalyst structure on catalytic activity also depended on the polymerization temperature and [H]/[E] ratio (Table 5.3) Using new catalyst, the higher catalytic activity was obtained at 50 0 C, which reflects the nature of tight interaction between the catalyst cation and the cocatalyst anion in the CGC systems [18] For example, due to increasing temperature from 40 0 C to 50 0 C, activity of catalyst 4 increases approximately three times This trend was able to predict that DCGC is more stable at high temperature In the case of 50 0 C, the activity order has a change between positions of catalyst 2 and 3 compare with the order at 40 0 C: 4 >> 3 > 2 > 1 The electronic effect of n-hexyl and n-octyl at high temperature perhaps happened In principle, n-octyl group has better electron-donating ability than n-hexyl and the catalytic activity can be increased by electron-donating group on the ligand, thus, catalyst 3 is more active than 2
The influence of the composition of comonomer in the feed on the catalytic activity of these catalyst systems was also examined by conducting the copolymerization of ethylene with 1-hexene under different comonomer concentrations As seen from the data in Table 5.2 and Table 5.3, the catalytic activities for all catalyst systems increase with the increase in comonomer concentration and keep the trend of effect of catalyst structure: 4 >> 3 > 2 > 1 with 50 0 C and 4 >> 2 > 3 > 1 with 30 0 C and 40 0 C This confirmed that the different branches on xylene bridge affected on the monomer attraction of active site b The incorporation of 1-hexene
The 1-hexene content of copolymers determined by the 1 H-NMR spectra is shown in Table 5.4 and Table 5.5
Table 5.4 The 1-hexene content results obtained at various monomer feed ratios [H]/[E] at 40 0 C and 30 0 C
Run Catalyst Tp ( 0 C) [H]/[E] a 1-hexene content in copolymer (%)
15 Dow 40 8 30.2 a monomer feed ratio (mol/mol)
Table 5.5 1-hexene content results obtained at various monomer feed ratios [H]/[E] at 50 0 C and 30 0 C
Run Catalyst Tp ( 0 C) [H]/[E] a 1-hexene content in copolymer (%)
27 4 30 4 24.1 a monomer feed ratio (mol/mol)
The results show that the 1-hexene contents of copolymers are concurrently influenced by polymerization temperature and composition of comonomer When increasing temperature from 30 to 50 0 C, the 1-hexene incorporations of all catalyst systems increase first and then decrease Whereas, the [H]/[E] ratio in feed increase from 2 to 8 at 40 0 C or from 2 to 4 at 50 0 C, the comonomer contents continuously increase
1H-NMR spectra of the copolymers obtained with catalyst 2 at various 1-hexene content and 40 0 C (Figure 5.2) or with different DCGC at [H]/[E] = 4 and 40 0 C
(Figure 5.3) show the clear relationship between the intensities of signal and the various 1-hexene incorporations of samples In the 1 H-NMR spectra, the methyl (CH3) signals (0.90-1.03 ppm) was well isolated from the methine (CH) and methylene (CH2) signals (1.30-1.82 ppm) and the 1-hexene contents were calculated from the integration values of the methyl signal and the combined signal of methine and methylene [19]
Figure 5.2 1 H-NMR spectrum of 1-hexene copolymer prepared by catalyst 2 with: (a) [H]/[E] = 2 (24,3 mol%); (b) [H]/[E] = 4 (31.6 mol%);
Figure 5.3 1 H-NMR spectrum of 1-hexene copolymer prepared by: (a) catalyst 1 ;
(b) catalyst 2; (c) catalyst 3; (d) Dow catalyst at 40 0 C, [H]/[E] = 4
[H] / [E] ratio in Feed (mol/ mol)
Figure 5.4 Variation of 1-hexene contents with [1-hexene] /[ethylene] ratios in feed at 40 0 C d a c b
As expected, the structures of catalysts also affect on the comonomer incorporation
The Figure 5.4 shows that the relation between 1-hexene contents and [H]/[E] ratio in feed depends on the catalyst structure in this trend: catalyst 3 > 2 > 4 > 1 > Dow at 40 0 C The curves of catalyst 2 and 3 have similar shapes and the catalyst 1 and 4 are not so much different Interestingly, our catalyst can reach 1-hexene content up to 27 mol% with [H]/[E] = 2, while using Dow CGC only get 20 mol% 1-hexene content with high monomer concentration in feed, [H]/[E] = 4 As above explanations, dinuclear CGC with xylene bridge can improve the catalytic activity because of the electronic and steric effect, which also affect on the incorporation ability of active center The octyl and hexyl group which are more flexible, lively and electric than iso-propyl can change the properties of active center to make the insertion of α-olefin into the metal-polymer chain easier Hence, the 1-hexene content in copolymers produced by catalyst 2 and 3 were higher than catalyst 1 and
4 On the other hand, the active site of catalyst 4 is more open than catalyst 1, so it can admit the bulkier α-olefin Because of this reason, catalyst 4 can give value of 1-hexene content same with or more than catalyst 1 With the influence of temperature, the observed 1-hexene content did not show so much change among our catalyst (about 24%) at lower temperature 30 0 C, whereas under the high temperature condition we can see the different 1-hexene content values between two pairs of catalyst: 2 and 3; 1 and 4 due to the activation of catalytic centers belong with the temperature c Melting temperature of polymer
DSC measurements on the copolymer samples indicate that both the melting temperature and the degree of crystallinity of the poly(ethylene-co-1- hexene)s are mainly dependent on the 1-hexene content The melting peak of copolymer disappears in the DSC curves when increasing the [H]/[E] ratio over 4 The DSC data of copolymers with low 1-hexene content were shown in Table 5.6 The DSC curves of some typical poly(ethylene-co-1-hexene) samples are shown in Figure
Table 5.6 Heat of fusion and degree of crystallization of the samples measured by DSC
Run Catalyst Tp ( 0 C) [H]/[E] a ΔH b (J/g) Xc c(%) Tm ( 0 C)
19 4 50 2 3.6 1.23 120.0 a monomer feed ratio (mol/mol) b Heat of fusion c Degree of crystallization calculated based on 100% defect-free polyethylene crystalline with a 292 J/g fusion heat [20]
Figure 5.5 DSC thermograms of the copolymers produced with catalyst 2 at
Figure 5.6 DSC thermograms of the copolymers produced at monomer feed ratio
Cat.1 Cat.2 Cat.3 Cat.4 Dow CGC d Molercular weight
Table 5.7 shows the GPC results of copolymer produced under various conditions
The presence of short-chain branches on poly(ethylene-co-1-hexene) complicates the process of obtaining accurate molecular weights The molecules containing short-chain branches have smaller hydrodynamic volumes than linear molecules with identical molecular weights; thus they elute at longer time This can give rise to serious errors in the determination of the molecular weight distribution when a single detector is used Therefore, the GPC results will be explained and compared in the acceptable range of the 1-hexene content
C ONCLUSIONS
We demonstrated that ethylene/1-hexene copolymers can be prepared successfully by the series of DCGC system having the variety of braches on the rigid bridge ligand at the general condition: [Cat.] = 20 μmol/l; [Al] / [Ti] = 4000; PE = 1 atm; t = 1 hour As expected, the influences of distinguished characteristic of catalysts on polymerization behavior such as catalytic activity, monomer incorporation ability, the molecular weight, and the microstructure of polymer manifested concurrent changes in polymerization temperature and monomer composition in feed Response of the catalyst structure, the catalytic activity was consistent in the order 4 >> 3 > 2 > 1 > Dow CGC, which indicates that the xylene bridge effectively improve polymerization activity Our catalytic activity increased when increasing the polymerization temperature as well as the 1-hexene concentration, for examples, increasing temperature from 40 0 C to 50 0 C, activity increases about 3 times Besides of the activity results, the 1-hexene content determined by both
1H-NMR and 13 C-NMR were affected by catalyst in the order 3 > 2 > 4 > 1 > Dow CGC The 13 C-NMR analysis shows that the average sequence length of ethylene in the microstructure of polymers is about 2.5 It means that our catalyst systems are efficient to incorporate 1-hexene in the polyethylene backbone The high activities of catalyst and 1-hexene content were explained by the relation between the steric and electronic properties of branches on xylene bridge While the short iso-propyl group can only rotate limit and cover the active site, the n-hexyl and n-octyl is more flexible and more electron-donating
The molecular weight distribution is broad because the asynchronous effect of branches on two active sites cause the performing of different active site in catalyst
The highest molecular weight was obtained with catalyst 1 containing the iso-propyl branch In summary, we can promote the controllability of the 1-hexene content as well as the molecular weight of polymer by our designed structure It turned out that the efficient incorporation ability of our catalyst can develop the variety of new copolymers by using other α-olefin.
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Full name : NGUYEN THI LE THANH
Date of Birth : September 26 th , 1979
Place of Birth : Binh Dinh province - Vietnam
Address of present school: B101 room, Precision Polymerization research lab
School of display and chemical engineering, Yeungnam university, 214-1 Daedong, Gyeongsan, Gyeongbuk 712-749, South Korea
Home Address : 172-11 dooli wonroom A502 Gyeyang-dong, Gyeongsan, Gyeongbuk, 712-120, South Korea
Guardians in Korea : Relationship: Supervisor Name : Professor SEOK-KYUN NOH
Email : sknoh@ynu.co.kr Address : B101 room, Precision Polymerization research lab School of display and chemical engineering, Yeungnam university, 214-1 Daedong, Gyeongsan, Gyeongbuk 712-749, South Korea
March 2006- present: Doctor course at department of Chemical Engineering and Technology, Yeungnam University, 214-1 Daedong, Gyeongsan, Gyeongbuk 712-749, South Korea
Major in Precision Polymerization research, Chemical Engineering
2002 - 2005: Studying at Faculty of Chemical Engineering, Hochiminh City University of Technology, Vietnam
Graduation Degree: Master of Engineering
Graduation research topic: Study on influence of organoclay to Nitrile rubber's properties
1997-2002: Studying at Faculty of Chemical Engineering, Hochiminh City University of Technology, Vietnam
Graduation Degree: Bachelor of Engineering
Graduation research topic: Study on advantages and disadvantages of dispersion of silica filled rubber compounds by creating crumb silica rubber from silica gel and natural rubber latex
Have knowledge in polymer material field
March 2006- present: assistant researcher at Yeungnam University, Korea
April 2002-present: lecture at Faculty of materials Technology, Hochiminh University of Technology, Viet Nam
이핵 하프티타노센에 의한 이소부틸에테르의 중합과 가지 달린 자이렌 다리로 연결된 이핵 압축형 촉매의 에틸렌 공중합 연구
영남대학교 대학원 응용화학공학과 응용화학공학 전공
(지도교수 노석균)
최근 다양한 dinuclear half-metallocene catalysts 가 olefin 중합반응을 효과적으로 진행하기 위해 빠르게 발전했다 두 개의 금속 중심, ligand 구조, 다리의 성질 사이의 협동 효과가 분자량, 분자량의 분배, stereochemistry 와 같은 고분자의 특성들을 맞출 수 있기 때문이다 하지만 이 촉매는 드물게 polar vinyl monomers 중합에 적용할 수 있었다 그래서 우리는 half dinuclear metallocene [(C 5 H 4 ) 2 (CH 2 ) n ][(TiCl 3 ) 2 ] [2(n=3), 3(n=6)]과 [(C 5 H 4 ) 2 (CH 2 ) n ][(TiCl 2 OR) 2 ] [4(n=3), 5(n=6)] 연속을 다른 polymethylene 다리로 합성했다 Mononuclear half-titanocene CpTiCl 3 [1]과
함께 dinuclear half-titanocenes 은 CH 2 Cl 2 용매 하에 공촉매로써 MAO 의 존재 안에서 isobutyl vinyl ether 를 중합하는데 사용되어 왔다 우리는 polymethylene 다리 길이와 금속 중심의 aryloxy group (-OR) 치환의 영향을 25 0 C, – 10 0 C, – 30 0 C 세 가지 중합 온도에서 실험했다 촉매의 구조는 중합 양식뿐만 아니라 생성된 고분자의 구조에도 중요한 영향을 미치는 것을 관찰할 수 있었다 –30 0 C 에서, dinuclear titanocenes 에 의해 생성된 촉매중합이 living character 한 개에서 고분자의 분자량과 단량체 전환 사이의 관계가 일차원적이라는 것을 보여준다 촉매의 활성도가 PIBVE 의 규칙성에 반하여 1 > 2 > 4 > 3 > 5 의 순서로 감소한다 추정된 racemic dyad value 는 1 < 2 < 3
< 4 < 5 의 순서로 증가한다 모아진 고분자는 높은 분자량(1x10 5 ~ 3x10 5 )과 좁은 분자량 분포(PDI ≤ 2.3)를 가지고 있다 흥미로운 사실은 메탈 중심의 aryloxy group 치환의 특성을 뚜렷하게 보여 주는 employed catalyst 에 의해 47%에서 56%의 다양한 레벨의 syndiotacticity 을 포함한 치환 가능한 생성된 고분자와 다른 다리 하나를 포함한 dinuclear half-titanocenes 은 고분자 stereoregularity 를 조절하는데 핵심 역할을 한다는 것이다
Dinuclear half metallocene 외에도 dinuclear contrained geometry catalysts 역시 polyethylene 의 분자량과 ethylene 의 copolymerizability 를 조절하기 위한 능력에서 기인한 metallocene 연구에서 주역할을 한다 우리는 이렇게 DCGC 와 일련의 단단한 다리들을 합성해보고, ethylene 공중합 거동의 영향에 대해 조사해 보았다 두 개의 다른 종류의 xylene THF 의 ligands 에 상응하는 tetralithium salts 와 두 개의 등가의 TiCl 3 (THF) 3 로 다루어진 xylene 다리에 기본으로 한 새로운 구조{TiCl 2 [N( t Bu) Si(Me) 2 ]C 9 H 5 } 2 {(CH 2 ) n [(R) 2 C 6 H 2 ] (CH 2 ) n }의 촉매를 디자인했다 첫 번째 형태는 촉매구조가 세 개의 alkyls: 1 (R= iso-propyl), 2 (R= n-hexyl), 3 (R= n-octyl)과 xylene 다리 (n = 1)에 기초하고 있다 다른 steric 과 alkyl 가지의 electronic 은 촉매적 특성들을 바꾸기 위한 활성부위로 작용을 한다 두 번째 형태는 촉매 세 개가 가지 (R=H): 4 (n=1), 5 (n=0), 6 (n=2)의 변화 없이 세 개의 다른 길이의 다리를 이용하여 형성하고 있다 다양한 다리의 길이는 촉매의 작용을 다르게 조절한다.