Cationic polymerization of vinyl ethers in the presence of silyl enol ethers

Vinyl ether oligomers with reactive end groups were prepared by alkylation of silyl enol ethers during propagation. Silyl enol ethers were added to the cationic polymerization of isobutyl vinyl ether, ethyl vinyl ether and methyl vinyl ether. The polymerizations were carried out under non-living conditions so that, in the absence of added silyl enol ether, MALDI TOF mass spectrometry gave evidence for end groups other than those derived from reaction with the methanol capping agent. Addition of either phenyl-1-(trimethylsilyloxy)ethlene or 1-methoxyphenyl-1-(trimethylsilyloxy)ethylene significantly reduced the fraction of end groups derived from intramolecular termination reactions, such as elimination, at temperatures between 21 and -78 degreesC. However, as in living systems lowering the reaction temperature increased the proportion of chains with the desired chain-end functionality (i.e. aryl ketone derived from alkylation of the silyl enol ether). alpha-beta Elimination also produced a population of isobutyl vinyl ether oligomers with alpha-beta unsaturated ketone end groups. Structure of an oligo(isobutyl vinyl ether) with a substituted phenyl ketone end group.