The Relation between the Nature of Growing Ion Pairs and the Reaction Rate Constants in Cationic Polymerization

IV. Isobutyl Vinyl Ether and t-Butyl Vinyl Ether

Abstract

Isobutyl vinyl ether and t-butyl vinyl ether were polymerized by BF8.0 (C2H5) 2 in various solvents. The limiting viscosity numbers of the polymers decreased with increasing the dielectric constant of the solvents used. This result was the same as that obtained in the polymerization of methyl vinyl ether. Monomer transfer constant ratios and spontaneous termination constant ratios were calculated and compared with those of methyl vinyl ether reported previously. From the experimental results it was found that the mechanisms of the monomer transfer and termination reactions in the polymerization of the butyl vinyl ethers were identical with those in the polymerization of methyl vinyl ether.
In the polymerization of the butyl vinyl ethers, however, both the transfer and termination reactions were mainly influenced by the dielectric constant of solvent rather than the polymerization temperature. This tendency was opposite to that of methyl vinyl ether. The activation energies of both reactions were nearly equal to zero in the solvent of higher dielectric constant.
These results were explained by the differences in inductive and steric effects among the alkyl groups, and those in the stability of the alkyl cations.