PROPOSAL ON THE STERIC COURSE OF PROPAGATION IN THE HOMOGENEOUS CATIONIC POLYMERIZATION OF VINYL AND RELATED MONOMERS

A stereochmical scheme of propagation was proposed for polymerizations of vinyl and related monomers by Friedel-Crafts catalysts. For the cationic propagation proceeding via the simple carbonium ion pair, the following two factors were considered to be of primary importance in determining the steric course of propagation-the conformation of the last two units of the propagating polymer segment and the direction of approach of the incoming monomer; the tightness of the growing ion pair. Thus, the front-side (less hindered site) attack to the carbonium ion gives rise to a syndiotactic placement and the back-side attack an isotactic placement.