Handbook of Polymer Synthesis Second Edition Episode 10 pps

10 Poly(vinyl aldehyde)s, Poly(vinyl ketone)s, and Phosphorus-Containing Vinyl Polymers Oskar Nuyken Technische Universita ¨ tMu ¨ nchen, Garching, Germany I. POLY(ACROLEIN) (This section was prepared by O. Nuyken, T. Po ¨ hlmann, R. Vogel and U. Anders.) Acrolein (propenal, acrylaldehyde) is the simplest unsaturated aldehyde, a colorless and volatile liquid with high toxicity and lachrymal irritability [1,2]. The first synthesis from glycerol and from fats by pyrolytic decomposition was described by Redtenbacher in 1848 [3]. Among its typical reactions he recognized that upon standing the fluid acrolein is spontaneously converted to a white, soli d, infusible, and insoluble pro duct he called disacryl. Later this substance has been proven to be the result of a spontaneous polymerization [4–8]. But it was not before the early 1940s that the career of acrole in as a ‘key compound’ in organic chemistry began [9,10]. It is mainly used in the production of D,L-methionine and acrylic acid. In polymer chemistry, however, none of the acrolein homopolymers has until now achieved technical significance, although the monomer is difunctional and highly reactive, and the polymers are susceptible to modification reactions [11–13]. A. Manufacture of the Monomer The oldest method for the preparation of acrolein, the acid-catalyzed thermolysis of glycerol (dehydration) at about 190  C, is still used today to obtain acrolein on a laboratory scale [3]: ð1Þ Copyright 2005 by Marcel Dekker. All Rights Reserved. By support of KHSO 4 the yield can be enhanced up to 50% [14]. Further possibilities are the reaction of gaseous propene with a suspension of HgSO 4 in aqueous sulfuric acid [15]: ð2Þ or the pyrolytic cleavage of 2,3-dihydropyrane [16,17]: ð3Þ The first efficient and profitable manufacturing process for acrolein was established by Degussa AG, Germany, in 1942 [8,18–20]. It depends on the gas-phase condensation (addition and dehydration) of formaldehyde with acetaldehyde at 300 to 320  C. In the presence of alkaline silica gel catalysts yields as high as 82% were achieved. ð4Þ In 1945, at the same time that the Shell Company commercialized the pyrolysis of diallyl ether [21], acrolein production began. ð5Þ With the supply of large amounts of propene in the 1950s the search began to find a system for its direct oxidation with molecular oxygen to yield acrolein. Attempts with cuprous oxide marked the beginning of the technical development of alkene oxidation in the gas phase by metal oxide catalysts [22]. But this system showed weak points in the conversion (20%) [23,24] and in the selec tivity, with the consequence that most of the propene added had to be recycled and many side products had to be removed. The development and introduction of the bismuth molybdate/bismuth phosphomolybdate system (Sohio, 1957) as a catalyst [25–27] and the following application for propene Copyright 2005 by Marcel Dekker. All Rights Reserved. oxidation opened the door to problem control. Specifically, for the system BiPMo 12 O 52 catalyst on a SiO 2 support, a reasonable selectivity (maximum 72%) could be observed. However, the propene conversion (57%) was still low. By a further development toward modern multicompound metal oxide catalysts [28] the propene conversion could be raised from 90 to 98% with a maximum yield of 80 to 90%. The main side product (ca. 5 to 10%) is acrylic acid, which can be removed by distillation. Examples of catalysts are: FeMoBiCoNiP oxide [29] (Nippon Kayaka), FeMoBiCoNiPK oxide [30] (Nipp on Kayaka), FeMoBiCoNiPSm oxide [31,32] (Degussa), MoBiFeCoWKSNaLi oxide [33] (Nippon Shokubai), MoBiFeP oxide [34] (Farbenwerke Hoechst). Common conditions for a good performance are: 300 to 400  C reaction temperature, 1.5 to 3.5 s contact time, 5 to 8 vol% propene concentration, 150 to 250 kPa inlet pressure, 1 : 10 to 20 : 1% molar ratio pro pene/air/gas passed over a solid catalyst of suitable shape. B. Radical Polymerization Acrolein, a member of the family of the polymerizable 2-alkenales and 2-alkenones, is provided with an extraordinary tendency for polymerization. Therefore, it may only be stored in the presence of a stabilizer (e.g., hydrochinone) in the absence of light, air, and moisture because of spontaneous polymerization. Even small amounts of initiator have the ability to force acrolein polymerization radically, anionically, or cationically, partly in an explosive manner. According to the existing reaction conditions and the catalysts used, it is possible to attain polymers of completely different shapes with characteristic features [9,13,35]. Radical polymerization prinicipal ly proceeds ac ross the vinyl functio n [1,2-addition; Scheme (6a)], whereas ionic polymerization yields products mainly by an addition at the carbonyl group [3,4-addition; Scheme (6b)]. However, the third possibility, 1,4-addition across the a,b and C,O double bond, is a subordinate process [Scheme (6c)] [12,36,37]. ð6aÀc Þ Copyright 2005 by Marcel Dekker. All Rights Reserved. Because of the polymerization across one of the two double bonds in acrolein polymers, the corresponding function remains pendant at the polymer backbone and is accessible to derivation reactions or for analytical purposes [9,37]. Radical polymerization occurs exclusively across the vinyl function. The remaining pendant formyl groups form hydrates and acetales without effort by intra- and inter- molecular condensation. The following structure elements are able to arise, including the characteristic tetrahydrop yrane rings [38–40]: ð7Þ Due to numerous chain cross-linkings by actetal groups, radically manufactured acrolein polymers are insoluble in water and in organic solvents. They decompose above 200  C without fusing. The polymerization itself is carried out in bulk, in aqueous solution, and in organic solvents. The Polymer precipitates from the solut ion and can be removed by filtration [11]. To start the polymerization the following initiators are used: inorganic peroxides [41] , organic peroxides [42,43], azo compounds [42,43], redox initiators [43–45], g-rays and others [46–49]. 1. Polymerization in Bulk The first spontaneous curing of acrolein observed was also the first polymerization in bulk [3]. Later, this observation was examined more closely [4–6,50–52]. Furthermore, a slow light- or g-ray-initiated polyme rization is possible, yielding highly cross-linked glassy products [46,53,54]. By means of AIBN or peroxides as initiators an explosive course of the reaction is observed that causes problems in the carriage of the reaction heat [42,55]. Therefore, working with only small amounts is recommended. 2. Precipitation Polymerization The heat problem does not occur during polymerizations in aqueous solution. At 20  C acrolein is soluble to 21.4% in water, wher eas the polymer precipi tates from the solution at molecular weights above 50,000 g/mol. The polymerization is started with water-soluble initiators or redox systems. In the case of redox initiators, H 2 O 2 ,S 2 O 8 2À ,P 2 O 4 4À , and organic peroxides and hyperoxides serve as oxidizing agents. Typical reducing agents are Copyright 2005 by Marcel Dekker. All Rights Reserved. Ag(I), Fe(II), and Tl(III) compounds, Na 2 SO 3 , NaNO 2 , and polyacrolein hydroxysu lfonic acid [13,41,42,56,57]. It is favorable to add the reducing agents to the aqueous solution of the oxidizing agent and acrolein. 3. Polymerization in Emulsion A very favorable way to obtain acrolein polymers having molar masses of some 100,000 g/mol is by emulsion polymerization [43,58–62]. In oil–water emulsions the water-soluble addition compounds of sulfuric acid (respectively, SO 2 ) and polyacrolein are used as very suitable emulsifiers to produce stable polymer dispersions. The emuls ion polymerization is started by water-soluble redox initiators. The acrolein polymers containing adsorbed or chemical bond SO 2 serve as reducing agents. Together with air in combination with oxygen donors [e.g., Fe(NO 3 ) 3 Á 9H 2 O, H 2 O 2 ,K 2 S 2 O 8 ], a powerful redox system is designed [63–65]. Further examples are the systems K 2 S 2 O 8 /AgNO 3 [60,61], K 2 S 2 O 8 /(NH 4 ) 2 SO 4 –Fe(II) compounds, and K 2 S 2 O 8 /Na 2 SO 3 [55]. Other soluble polymers, such as gelatine, PVA, or methyl cellulose, combined with sulfuric acid or SO 2 , also accomplish the double function of emulsifier and reducing agent [63,64]. Polymerization in the inverse emulsion (water–oil) has also been described [66,67]. Aliphatic and aromatic hydrocarbons make up the continuous phase, and acrolein exists in the aqueous phase. 4. Polymerization in Solution The monomer is soluble in numerous solvents; however, the polymer precipitates from most of these solvents at about 15% conversion during radical polymerization. Molecular weights up to 100,000 g/mol and aldehyde contents above 65% can be achieved when the polymerization is carried out in polar solvent s such as DMF, g-butyrolactone, or pyridine by means of hydroperoxides and nitrous acid derivatives as redox catalysts [68]. Deviations from this behavior are observed if DMF is used as solvent and the polymerization is initiated by AIBN. A microgel is formed here; after 16% conversion the clear reaction solution turns into a transparent gel [69]. Polymerization in the presence of methanol initiated by means of azo compounds or peroxides does yield soluble poly(acrolein), presumably because of the polymer’s molecular weight [70]. 5. Radiation-Induced Polymerization Bulk polymerization of acrolein under the influence of g-rays yields a highly cross-linked glassy polymer, which is completely insoluble in organic solvents and also in aqueous sulfuric acid. Gamma-ray-induced polymerization in solution, especially in water, is much faster than in bulk [46–48 ,54]. Investigations of radiation-induced polymerizations in bulk or in aqueous solution by means of a 60 Co source yielded microspheres of different size containing reactive formyl functions [49,71,72]. 6. Solubilization of the Polymers To solubilize the products of radically induced acrolein polymerization, the following procedures are used. Copyright 2005 by Marcel Dekker. All Rights Reserved. Disproportionation of the aldehy de and acetale groups pending on the polymer backbone by means of sodium hydoxide solution (Cannizzaro reaction) [73–75]: ð8Þ Formation of water-soluble addition products by the action of sodium bisulfite and aqueous sulfurous acid [76–78]: ð9Þ By dialysis of the primary addition product, the following equilibrium can be forced to the right side yielding water-soluble, SO 2 -free acrolein hydrate [79]: ð10Þ C. Ionic Polymerization 1. Anionically In the presence of alkaline metal hydroxides or carbonates, acrolein is converted into oily resinous products [5,6]. This reaction proceeds in a vigorous-to-explosive way by means of strong bases and amines [13]. In the 1950s this techniques was used to produce polymers by anionic polymerization in solution under well-defined conditions. In THF, DMF, toluene, glyme, and other solvents, products with melting and softening points between 90 and 200  C were obtained which were soluble in organic solvents but insoluble in sulfurous acid [80,81]. Structural analysis of the polymer’s repetition units gave rise to the assumption that chain growth occurs mainly across the carbonyl group (3,4-polymerization, - structure units) [37,81]. Furthermore, there is addition across the vinyl function (1,2- addition) and across both functional groups (1,4-addition) [82,83]. The latter takes place only on a very small scale. Consequently, copolymers are formed that contain the following structure elements: , partly in block arrangement (n þ m ¼ 1; m ¼ 0.7 to 0.8) [84]. In a water-free medium chain growth polymerization can be initiated by numerous metal-organic or basic compounds, such as trityl sodium [81], butyl lithium [80,81], naphthyl sodium [80,81], benzophenone potassium [81], sodium methoxide [80,81], lithium organocuprates [85] and rhodium(I) complexes [86] or ammonia [87], tert-phosphines [80,88], aliphatic amines [89], cyclic amines [90], and aromatic amines (pyridine [91,92], Copyright 2005 by Marcel Dekker. All Rights Reserved. imidazole [93,94], N-ethylimidazole [95]). The reaction temperatures range from À 60  Cto þ 25  C, whereby the reaction rates as well as the properties of the products (composition) are influenced. Higher temperatures lead to products having a higher content of aldehyde side groups and a lower content of vinyl side groups. Weaker bases and solvents with lower polarity also favor the formation of polymers with aldehyde side groups [81]. Acrolein can be polymerized by alkali cyanides in polar solvents such as THF or DMF [96,97]. At reaction temperatures below À 10  C, only 3,4-connected products were obtained. 2. Cationically Few sources describe the cationic acrolein polyme rization in bulk or in homogeneous solution [7,12,42,80,98]. Using trifluoroborane-diethyl ether or triethyloxonium-tetra- fluoroborate as initiators carbonyl and vinyl group containing polymers are obtained at reaction temperatures ranging from À 80  C to room temperature. The carbonyl content of these polymers varies from 9 to 15 mol%. For this polymerization polar solvents such as nitromethane or nitrobenzene are favorable. When the polymerization is stopped at low conversion soluble products (cf. in 1,4-dioxane, CHCl 3 , THF, pyridine) are obtained. Adding tert-amines during the last step of the polymerizations results in the highest content of carbonyl polymerization [9]. At higher conversions or at prolonged storage the products become cross-linked and insoluble. All these products soften between 80 and 120  C. D. Copolymerizations 1. Radical Copolymerization For a list of various characteristics of radical copolymerization, see Table 1. 2. Graft Copolymerization Acrolein can be grafted onto poly(methyl methacrylate), cellulose, and poly(ethylene) by g- or electron-beam radiation. 1. A foil of poly(methyl methacrylate) was swollen in aqueous or methanolic acrolein solution and then exposed to g-radiation of a 60 Co source. Graft polymers with aldehyde groups were formed, which show the specific aldehyde- type reactions [46]. 2. Cellulose dispersed in an acrolein solution (solvent: water, ethanol, acetone, ether, or benzene) was treated with g-radiation of a 60 Co source at 40 to 43  C. In addition to the formation of a network of cellulose, homopolymerization of acrolein was observed. Homopolymerization of acrolein could be avoided if cellulose was treated with gaseous acrolein at a pressure of 10 À3 torr before radiation [106]. 3. Acrolein was grafted onto poly(ethylene) which was exposed to electron beams. The remaining aldehyde groups could be transformed into hydrazon e, oxime, and oxyacid units [107]. 3. Oxidative Copolymerization Acrolein and acrylic acid were copolymerized in aqueous H 2 O 2 solution at 60 to 90  Cto form poly(aldehyde carbon acids). The Cannizzaro reaction took place if an aqueous Copyright 2005 by Marcel Dekker. All Rights Reserved. solution or suspension of this polymer material was treated with aqueous NaOH. The aldehyde functions disproportionated into carboxylate and alcohol groups to form poly(hydroxy carboxylates) [108,109]. 4. Anionic Copolymerization Acrolein was anionically copolymerized with acryl amide and methyl vinyl ketone (r 1 ¼ 2.02, r 2 ¼ 0.06) at 0  C in THF with imidazole as an initiator [110]. Copolymeriza- tions of acrolein with various aldehydes (e.g., acetaldehyde and benzaldehyde) were carried out in THF at À 30  C with NaCN as initiator [111]. 5. Block Copolymers 1. Living oligomers of butadiene were functionalized by the addition of acrolein or ethylene oxide and then treated with acrolein to yield block copolymers. The homopolymerization of acrolein could not be avoided [112,113]. 2. Short poly(acrolein) blocks were formed, if a,o-disodium oligobutadiene (initiated with sodium naphthal ene in THF at À 40  C) was treated with Table 1 Parameters of the radical copolymerization. Monomer M 2 r 1 r 2 Temp (  C) Initiator Solvent Refs. Acrylic acid 0.50 Æ 0.30 1.15 Æ 0.20 54 AIBN Water a [99] 2.40 Æ 0.50 0.05 Æ 0.05 75 AIBN Water b [99] 6.70 Æ 3.00 0.00 80 AIBN Water c [99] Acryl amide 2.0 Æ 0.05 0.76 Æ 0.02 20 K 2 S 2 O 8 þ AgNO 3 Water [100] 1.69 Æ 0.1 0.21 Æ 0.02 50 AIBN DMF [101] Acryl nitrile 1.09 Æ 0.05 0.77 Æ 0.1 20 K 2 S 2 O 8 þ AgNO 3 ; H 2 O 2 þ NaNO 2 Water [100] 1.60 Æ 0.04 0.52 Æ 0.02 50 AIBN DMF [101] Butyl acrylate 1.6 0.6 50 K 2 S 2 O 8 Water [102] 1.6 0.6 60 AIBN Dioxane [103] 1.2 0.6 60 AIBN Ethyl acrylate 1.6 0.6 50 K 2 S 2 O 8 Water [102] AIBN Dioxane [103] Maleic hydrazide 16 0 60 AIBN DMSO [104] Maleimide 3.20 0.12 60 AIBN DMSO [104] Methacryl nitrile 0.72 Æ 0.06 1.20 Æ 0.08 50 AIBN Dioxane [101] Methyl acrylate $ 0 7.7 Æ 0.2 20 K 2 S 2 O 8 þ AgNO 3 Water [100,101] 1.6 0.6 50 K 2 S 2 O 8 Water [102] 1.2 0.6 60 AIBN Dioxane [103] Methyl 0.5 1.0 50 K 2 S 2 O 8 Water [102] methacrylate 0.8 1.2 60 AIBN Dioxane [103] Styrene 0.034 0.32 50 K 2 S 2 O 8 Water [102] 0.25 0.25 60 AIBN Dioxane [103] 0.22 0.33 50 AIBN Dioxane [105] Vinyl acetate 3.33 Æ 0.1 0.1 Æ 0.05 20 K 2 S 2 O 8 þ AgNO 3 Water [100] 2-Vinyl pyridine $ 4 $ 0 50 AIBN DMF [101] a pH 3. b pH 5. c pH 7. Copyright 2005 by Marcel Dekker. All Rights Reserved. acrolein. Homopolymerization of acrolein did not take place. The acrolein units could be cross-linked after an UV cure to form a poly(acrolein) network that can be used as photo-polymer layers to prepare negative printing plates [114]. 6. Graft Copolymerization Acrolein could be grafted onto imidazole-containing polymers [poly4(5)-vinylimidazole) or copolymers of 4(5)-vinylimidazole with acryl amide, styrene, 1-vinyl-2-pyrrolidone, 4-vinylpyridine, acrylates, and methyl vinyl ketone] in ethanol or an ethanol–water mixture at 0  C under nitrogen [115–117]. 7. Cationic Copolymerization Cationic copolymerization of acrolein with styrene took place in methylene chloride, toluene, and 1-nitropropane with bortrifluoride-etherate as a catalyst at different temperatures (À 78  Cto0  C) [118]. E. Modification Reactions of Poly(acrolein) 1. Radically Polymerized Acrolein (Redox Poly(acrolein)) Redox poly(acrolein) is one of the most reactive polymers and susceptible to a number of modification reactions that lead to high conversions under mild conditions [9,11,37]. Containing one pendant aldehyde function per repetition unit – either free or masked – poly(acrolein) possesses functional groups and can react basically in the following ways [37,39,40]: (a) As a Polymeric Monoaldehyde (i.e., after the pyran rings’ cleavage, the aldehyde functions developed react independent of each other). Examples are oxidations [119] (e.g., with peracetic acid) and reductions [120,121] [e.g., to poly(allylalcohol)] of the C,O group, or reactions with alcohols to acetales [122], amines to imines [39,123], hydroxylamine to oximes [124], or phenylhydrazine to hydrozones [39,123]. The latter serve for the quantitative determination of the aldehyde group content. (b) In Condensation Reac tions. Representative reactions are aldol condensation [125,126] with formaldehyde taking place at the polymers’ a-carbons, and Knoevenagel condensation [40,127] with C,H acidic compound s (e.g ., malodinitrile). ð11Þ ð12Þ Copyright 2005 by Marcel Dekker. All Rights Reserved. (c) As a Polymeric Dicarbonyl Compounds. For reasons of their masking in the form of pyran rings, reactions are favored in which two adjacent carbonyl functions are involved. The intramolecular disproportionation reaction by Cannizzaro serves as a well- known example. Un der the action of alkal i and due to the proximity and reactivity of the aldehyde groups, polymers with pendant hydoxymethyl (CH 2 OH) and carboxylate (COO À ) groups are formed [73–75]. ð13Þ (d) As a Polymeric Semiacetate. The semiacetale hydroxy groups are able to perform characteristic reactions without cleaving the pyran ring structure (e.g., thiol addition) [128]. ð14Þ Because of the insolubility of redox poly(acrolein) [129], modification reactions must always start in heterogeneous systems and lead to soluble products gradually. The already presented water-soluble products of the reaction between poly(acrolein) and Na 2 SO 3 or H 2 SO 3 [76–78] are still better precursors for modification reactions than is native redox poly(acrolein). They permit a reaction performance in homogeneous media. Apart from conversions with low-molecular-weight compounds, solub le and insoluble redox poly(acrolein) can react with high-molecular-weight substrates. Connec- tions with the following in vivo and in vitro occurring polymers are good examples of that behavior: poly(vinyl alcohol) [130,131], cellulose [130–132], proteins [130,131,133,134] (e.g., collagen, gelatine [135]), enzymes [130,136,137], lectins [138,139], erythrocytes [140–142] and lymphocytes [140], leukemia cells [140,142], antibodies [133,143,144], and metal complexing agents [145]. 2. Anionically Polymerized Acrolein Due to the high portion of pendant vinyl groups, the following reactions of this polymer material are possible: 1. Co- and graft polymerization with vinyl and acryl monomers in the form of a two-step copolymerization process [146]. 2. Autoxidation of the double bond and a subsequent connection with the polymers’ remaining aldehyde functions [81] . 3. Light-induced cross-linking across the vinyl group [147]. Copyright 2005 by Marcel Dekker. All Rights Reserved. [...]... products obtained are 1 : 1 copolymers Although these reactions run without any radical initiator, shown by the addition of hydroquinone, the yield of copolymer can be increased in the presence of traces of benzoyl peroxide [309] The copolymerization behavior of MVK can be changed by complexation of the monomer with Lewis acids [ 310] The 2 : 1 complex (MVK)2ZnCl2 can be copolymerized with allyl benzene,... metal and gave a conversion of 90% after 20 h reaction Lithium, sodium and potassium gave rise to crystalline, possibly isotactic polymers during heterogeneous polymerization in n-heptane, benzene, or toluene and amorphous polymers during homogeneous polymerization in tetrahydrofuran The softening points of the crystalline polymers were about 240  C [342] Atactic polymer of t-butyl vinyl ketone was... step: ð18Þ The fact that the rate of polymerization of crotonaldehyde increases with the dielectric constant of the solvent is evidence for an ionic mechanism of the polymerization An increase in dielectric constant of the medium will favor energetically an increase in the rate of initiation and the stabilization of the zwitterion [172] It should not influence the rate of propagation and termination Radical... cross-linkages 2 Copolymerization in the Presence of Lewis Acids Despite the results of pure radical copolymerization, it is more difficult to produce copolymers of MVK with styrene under ionic conditions Only a small amount (about 2%) of styrene is incorporated in the polymer if catalysts such as Et3Al, Et2Zn, and Et2Cd are used [276] It was more attractive to copolymerize MVK with styrene under catalysis of Lewis... structure is proposed: ð21Þ The anionic polymerization of crotonaldehyde was also carried out under high pressure with Et3N [186] It was found that the melting point and molar mass of the polymer increase linearly with rising pressure or temperature 4 Cationic Polymerization and Field Polymerization Cationic polymerization of crotonaldehyde is less important than anionic polymerization With (EtO)3Al or (i-PrO)3Al... initiators, rather unstable polymers were obtained [187]; with H3PO4 and PCl5 only oil was formed [188] Polymerization of crotonaldehyde can also be induced by high electric fields (several 107 V/cm) [189] Field polymerization results in the growth of organic semiconducting micro needles with side-chain cross-linking and Pmax ¼ 3 5 Step-growth Polymerization The polymerization of crotonaldehyde and several... tris(pentafluorophenyl)boranes lead to a rapid polymerization by means of group transfer polymerization of MVK [320]: ð53Þ D Copolymerization 1 Radical Copolymerization As already mentioned, PMVK has poor mechanical properties Therefore, numerous copolymers were synthesized with a large number of vinyl monomers and dienes MVK is Copyright 2005 by Marcel Dekker All Rights Reserved Table 6 Reactivity ratios of some comonomers... 4 4 ð31Þ The decrease in pH value that results was investigated with respect to the viscosity of the polymer solution and the structure of the polymer 4 Anionic Polymerization Anionic polymerization of methacrolein was investigated by several authors [244–251] Homogeneous initiators are the anion radicals of naphthalene [242,246], 2,4-dimethylbenzophenone [247], 4-methylbenzophenone [247], 1-benzoylnaphthalene... therefore the following polymer structure (50) is observed instead of the ‘normal’ 1,2 addition [296]: ð50Þ Another interesting initiator for MVK is the system pyridine-water An initial addition product, b-ketobutanol, is formed, which in the presence of a base, yields a 1,2 addition polymer [297] 2 Cationic Polymerization Cationic polymerization of MVK is certainly not the method of choice However, if... petroleum ether polymerization was observed [298] Acid-catalyzed polarography of MVK in methanol is also considered to be a cationic polymerization For the polymer an alternating ketoneether copolymer structure was suggested [299,300] The following reaction mechanism is Copyright 2005 by Marcel Dekker All Rights Reserved proposed (Structure (51)): 3 Group Transfer Polymerization A nonionic way of polymerizing . treated with g-radiation of a 60 Co source at 40 to 43  C. In addition to the formation of a network of cellulose, homopolymerization of acrolein was observed. Homopolymerization of acrolein could. rate of polymerization of crotonaldehyde increases with the dielectric constant of the solvent is evidence for an ionic mechanism of the polymerization. An increase in dielectric constant of the. investigated with respect to the viscosity of the polymer solution and the structure of the polymer. 4. Anionic Polymerization Anionic polymerization of methacrolein was investigated by several