RING OPENING POLYMERIZATION (r o p)

RING OPENING POLYMERIZATION R O P oxirane I/ GENERAL CHARACTERISTICS * Polymerizability 3,4 > 8 > 5,7 6-membered ring ?? cis- and trans-8-oxabicyclo[ 4.3.0]-nonane FREE OF STRAIN  I does not polymerize II  tetrahydrofuran ring is twisted  highly strained * Polymerization Mechanism and Kinetics Cationic ROP Anionic ROP II/ Cyclic ether : * Anionic Polymerization of Epoxides Propylene oxide : head to tail structure Ex : ferric chloride–propylene oxide adduct ClFe[OCH(CH3)CH2Cl]2 Anionic coordination initiators Reaction rate : Degree of polymerization Exchange Reactions Epoxide polymerizations taking place in the presence of protonic substances such as water or alcohol involve the presence of exchange reactions Dormant the addition of alcohol or other protonic substance is useful for control of polymer molecular weight Number-average degree of pol. [...]... Both the polymerization rate and polymer molecular weight decrease along with a broadening of the polymer molecular weight Chain Transfer to Monomer Species VII and VIII reinitiate polymerization of propylene oxide R O B B R O R O B R CH3 EX: EtO , K O CH3 CH3 O CH2 CH H CH3 O O OK EtO + n CH2 CH O CH2 + O CH3 O CH2 CH3 CH2 CH O CH2 CH CH2 CH CH2 O OH CH3 O + CH2 CH O CH2 O CH2 CH CH3 O * Cationic Polymerization. .. polymer molecular weights are considerably lower attachment of nitrogen to C+, proton transfer from one N to the other N, ring opening of the HO-containing ring, and transfer from HO-C+ to N with formation of XXV Propagation : * Anionic Polymerization - Use of Strong Base Alone Strong bases such as alkali metals, metal hydrides, metal amides, metal alkoxides, and organometallic compounds initiate the polymerization. .. O * Cationic Polymerization Propagation  oxonium ion A- : counterion The a-carbon of the oxonium ion is electron-deficient because of the adjacent positively charged oxygen Propagation is a nucleophilic attack of the oxygen of a monomer molecule on the a-carbon of the oxonium The nucleophilic reaction is an SN2 reaction for most cyclic ethers [Saegusa et al., 1976] However, SN1 ring opening has been... Polyester 5-membered lactone ( γ-butyrolactone) ? 6-membered lactone ( δ-valerolactone) ? * Anionic Polymerization Initiation : Propagation: The experimental evidence for the acyl–oxygen cleavage mechanism comes from endgroup analysis of the polymer Cationic Polymerization initiation by methyl carbocation derived from CH3OSO2CF3 or (CH3)2I+SbF6 Cationic ROP of lactones in the presence of an alcohol... of protonic compounds such as HCl or RCOOH in place of ROH or H 2O yields a different result in most systems When such substances take part in the exchange reaction, the result is not exchange as described above but inhibition or retardation since an anion, such as Cl- or RCOO-, possesses little or no nucleophilicity Reinitiation does not occur or is very slow The polymeric alcohols are no longer dormant... and the ratio of the rate constants for the two reactions Assuming that the two rate constants are comparable, AM ROP becomes the dominant process at high [ROH] and low [M] Thus, AMM is carried out under monomer-starved conditions The instantaneous monomer concentration is very low, but monomer is continuously added to the reactor at a rate equal to its rate of consumption Cyclic oligomer is minimized... trifluoromethanesulfonic (triflic) acids initiate polymerization via the initial formation of a secondary oxonium ion  tertiary oxonium ion Lewis acids such as BF3 and SbCl5, almost always in conjuction with water or some other protogen, initiate polymerization of cyclic ethers Initiator + Coinitiator  BF3 H 2O, H+(SbCl6) - Alkyl or acyl halide with a Lewis acid generates carbocations and acylium ions... extent of ACE For example, conventional ROP of propylene oxide with BF 3 in CH2Cl2 at 25C gives mostly cyclic oligomers, the yield of cyclic tetramer alone is 50% The cyclic tetramer drops below 1% when the reaction is changed to an AM polymerization by including an alcohol and slowly adding monomer AM polymerization has been successfully demonstrated for the synthesis of telechelic polymers of propylene... Termination and Transfer Processes Transfer Reactions Common mode  Chain transfer to polymer  broadening of the MWD Competition between propagation and chain transfer to polymer Propagation is favored on steric grounds since attack by monomer is less hindered than attack by the ether oxygen in a polymer chain Cationic ROP of ethylene oxide is not useful for the synthesis of linear polymer, but is used to... proceeds by an activated monomer mechanism similar to that for cyclic ethers [Endo et al., 2002; Lou et al.,2002] Propagation proceeds by nucleophilic attack of the hydroxyl end group of a propagating chain on protonated (activated) monomer: Enzymatic Polymerization Enzyme  Lipases IV.LACTAMS (cyclic amides) * Cationic Polymerization Cationic initiation is not useful because the conversions and polymer . of alcohol or other protonic substance is useful for control of polymer molecular weight Number-average degree of pol. The use of protonic compounds such as HCl or RCOOH in place of ROH or. anion, such as Cl - or RCOO - , possesses little or no nucleophilicity. Reinitiation does not occur or is very slow. The polymeric alcohols are no longer dormant but are dead. Both the polymerization. O CH 3 O CH 3 * Cationic Polymerization Propagation  oxonium ion A - : counterion The a-carbon of the oxonium ion is electron-deficient because of the adjacent positively charged oxygen.