Polyemrization_reactions__Chem_358_S06

Polyemrization_reactions__Chem_358_S06 - Anionic...

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1 Anionic Polymerization of Methacrylates O H 3CO OMe O MeO O H 3CO O MMA 2 + OMe O MeO 2 C H 3 CO O MeO 2 C n MMA 3 2 + n PMMA H + Anionic Polymerization of Methacrylates Major Termination Reaction Back-biting reaction: Dieckmann Condensation (Intramolecular Claisen Condensation) R O OMe CO2Me CO2Me O OMe O OMe CO2Me CO2Me P CO2Me CO2Me P O -MeO Dead Polymer Chain end. Can’t continue the Michael type addition to form polymer Group Transfer Polymerization OSiMe3 MeO OMe O MeO O Me3SiO OMe OMe O MeO2C O OMe MeO2C SiMe3 HF 2 HF 2 n H PMMA 1 MMA 2 MMA 3 2 + n + This is a Si-mediated Michael-type (conjugate addition to α , β -unsaturated esters and related compounds. Aldol Group Transfer Polymerization This is similar to aldol addition between aldehydes and the corresponding enolates. This is usually accompanied by dehydration leading to α , β -unsaturated product. The presence of silyl group minimizes the dehydration reaction. A catalyzed sequential addition of silyl enol ethers (nucleophiles, monomers) to aldehydes and ketones (electrophiles, initiators). Vinyloxy silane or silyl enol ether O + O—SiMe2t-Bu O OSiMe2t-Bu n OSiMe2t-Bu t-BuMe2SiO O OSiMe2t-Bu ZnBr2 n n-Bu4N + F HO O OH n Silylated polyvinyl alcohol Polyvinyl alcohol The aldol addition and condensation Aldol Group Transfer Polymerization O O O O O H + O —H2O H O O H hydrogen bonding possible
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2 Aldol Group Transfer Polymerization Suggested Mechanism + PhCHO ZnBr 2 Ph H O ZnBr 2 O R 3 Si O Ph Br 2 Zn H O R 3 Si O R Br 2 Zn H Ph H OSiR 3 O + ZnBr 2 R 3 SI O H H OSiR 3 OSiR 3 O Polymer Large molecule consisting of many relatively small chemical units covalently linked into a chainlike structure Monomer Any substance capable of chemical combination into polymer chains Repeat Unit Simplest sequence repetitively occurring in the polymer Degree of polymerization (DP) Total number of repeating units; related to chain length and molecular weight. A given polymer sample contains varying lengths of chains; hence, we normally refer to average degree of polymerization . Calculated from
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Polyemrization_reactions__Chem_358_S06 - Anionic...

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