Dotsevi Yao Sogah

Synthesis of reactive-ended acrylic polymers by group transfer polymerization: initiation with silyl ketene acetals

Abstract Living methacrylate polymers are obtained at room temperature and above by initiation with ketene silyl acetals in the presence of a soluble bifluoride catalyst. During the polymerization, a trialkylsilyl group is transferred from the living chain end to incoming monomer. The new procedure has thus been named group transfer polymerization (GTP). Monodisperse polymers with predetermined molecular weights as high as 100,000 can be obtained by adjusting the monomer/initiator ratio. Telechelic poly(methyl methacrylate) with hydroxy or carboxy ends can be obtained by using an initiator containing a protected hydroxy or carboxy group and coupling the resulting living polymer.

Group Transfer and Aldol Group Transfer Polymerization

Two new methods for polymer chain formation involving transfer of trialkylsilyl groups have recently been reported. One gives ‘living’ polyacrylics at ambient temperatures, the other gives ‘living’ silyl-capped poly(vinyl alcohol) (PVAL). In the first method, termed group transfer polymerization (GTP),1–7 a silyl ketene acetal initiator (1) reacts with a monomer by a Michael addition. During the addition, the silyl group transfers to the monomer generating a new ketene acetal function (2). The new ketene acetal reacts with additional monomer in a repeated fashion to give a living polymer (3). The process is illustrated in Scheme 1 for methyl methacrylate (MMA).

ALDOL-GTP in Controlled Synthesis of Vinyl Alcohol Polymers

Sequential silyl aldol condensation involving aldehydes and silyl vinyl ethers gives monodisperse poly(silyl vinyl ether) whose molecular weight (({overline {text{M}} _{n,}})1000-160,000) is controlled by the aldehyde initiator. The new process, termed aldol-group transfer polymerization (aldol-GTP) involves a silyl group transfer from monomer to the carbonyl oxygen of either the initiator or the living polymer, leading to generation of a new terminal aldehyde functional group. The reaction is catalyzed by Lewis acids and can be initiated by other electrophiles, e.g., alkyl halides and acetals. The living polymers are stable, neutral materials whose hydrolytic stability depends on the bulkiness of the sily group. In general, aromatic aldehydes tend to react more cleanly as initiators than do aliphatic aldehydes. Unlike the GTP of methyl methacrylate in which the silyl group is transferred from the initiator to the monomer, aldol-GTP involves a transfer of silyl group from monomer to initiator. Some of the advantages of aldol-GTP over existing methods such as cationic polymerization include operability over a broad temperature range, complete monomer conversion, living polymer formation, very good molecular weight control, and facile block copolymer synthesis. It permits control of hydrophilicity of block copolymers.