Structure and reactivity of α,β‐unsaturated ethers. III. Cationic copolymerizations of alkenyl alkyl ethers

The relative cationic polymerizabilities of the geometrical isomers of various alkenyl alkyl ethers were studied both in copolymerizations with each other and in their respective copolymerizations with vinyl isobutyl ether as standard. Copolymerizations were carried out in methylene dichloride at −78°C. with boron trifluoride etherate as catalyst. The cis isomers have been found to be more reactive than the corresponding trans isomers. A primary alkyl substituent on the β‐cis position of vinyl ethyl ether enhances the reactivity. Yet the steric effect is noticeable when the substituents are bulky. Compounds substituted with cis‐β‐isobutyl and with β‐dimethyl showed little tendency to homopolymerization. It was proved that the polymer ends derived from cis and from trans monomers are respectively different in character because of the restricted rotation of the end unit around the terminal carbon–carbon bond. The alternation tendency, remarkable in the copolymerization of cis monomers with vinyl ether, was explained in terms of the cis‐opening mechanism.