Cationic polymerization of α·β‐disubstituted olefins. Part X. Effect of polymerization conditions on the steric structure of poly(methyl propenyl ether)

The effect of polymerization conditions on the steric structure of the polymer was studied for the polymerization of methyl propenyl ether (MPE) catalyzed by BF3·O(C2H5)2. The steric structure of the α‐ and β‐carbon atoms of the polymers were measured by NMR spectroscopy. The threo‐meso configuration of the α‐ and β‐carbons of the polymer obtained from mixtures of cis‐ and trans‐MPE increased with increasing amount of trans‐isomer in the monomer mixture. We conclude that the pure trans‐isomer would give a threo‐di‐isotactic polymer. As the polarity of the solvent increased, the proportion of threo‐meso structure decreased in the polymer obtained from trans‐rich monomer, but it increased in the polymer obtained from cis‐rich monomer. The effect of the solvent on the steric structure of the polymer obtained from the cis‐isomer was greater than on that of the polymer from trans‐isomer. An interaction between the β‐methyl group of the attacking monomer and that of the penultimate unit was recognized on the basis of the change in the steric structure of the polymer with polymerization temperature. The α‐carbons of the polymer obtained were found to have the racemic configuration whilst the β‐carbons are hardly ever racemic. The mechanism of the propagation reaction is discussed on the basis of these results.