| Abstract: | Propagation mechanism in the cationic polymerization of alkenyl ethers was investigated through the effect of the bulkiness of alkoxy groups on the steric structure of a polymer. In polymerization with BF3O(C2H5)2 in toluene at ?78°C, trans-propenyl ethers having less bulky alkoxy groups–methyl, ethyl, and benzyl propenyl ethers–produced a stereoregular polymer having a threo-meso structure, and the cis isomer a nonstereoregular one having threo-meso and racemic structures. On the other hand, in the polymerization of propenyl ethers having bulky alkoxy groups–isopropyl and 1-methylpropyl propenyl ethers–the trans isomer yielded a nonstereoregular polymer with threo-meso and racemic structures, and the cis isomer a stereoregular one with a erythro-meso structure. This result suggests that a bulky alkoxy group plays an important role in determining the steric structure of the polymer by repulsion between the alkoxy groups of a growing chain end and of a monomer. The effect of solvent polarity on the steric structure of a polymer was also studied. |
