The cationic polymerization of isobutyl vinyl ether was conducted with a variety of triphenylmethyl salts as initiators, and the steric structure of the polymer was determined from the methylene dyad peaks in the13C-NMR spectra. The fraction of the isotactic dyad increased with the increase in the counteranion size from BF4-to CIO4− to BC14−, and then decreased: A trend similar to that observed for ɑ-methylstyrene. The correlation seems to be more complex for larger counteranions, and a periodical influence was clearly noticed. These results were explained by considering the tightness of the propagating ion-pair. Pentacoordinate counteranions showed peculiar influences in that the polymer structure was influenced by the counteranion concentration. The molecular weight distribution was unimodal, suggesting that a single propagating species is present.
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