STUDIES ON PROPAGATING SPECIES IN CATIONIC POLYMERIZATION OF STYRENE DERIVATIVES BY ACETYL PERCHLORATE OR IODINE .1. BIMODAL MOLECULAR-WEIGHT DISTRIBUTION OF POLYMERS PRODUCED BY ACETYL PERCHLORATE OR IODINE

To investigate the nature of the propagating species in cationic polymerization of para-substituted styrenes, p-chlorostyrene (pCIS), p-methylstyrene (pMS), and p-methoxystyrene (pMOS), were polymerized with acetyl perchlorate or iodine in various solvents at 0 degree C, and MWD of the polymers was measured by means of gel-permeation chromatography. When CIO//4** minus was a counterion, poly(pCIS) having a bimodal MWD was produced, while polymers of pMOS and pMS possessed a unimodal MWD, regardless of the solvent polarity. When more nucleophilic I** minus (or I//3** minus ) was a counterion, however, polymers having a bimodal MWD were produced from pMOS and pMS. These results showed that either dissociated or nondissociated propagating species existed in the cationic polymerization of styrene derivatives with acetyl perchlorate or iodine, and that the type of MWD was strongly dependent on the stability of the growing cation and the nucleophilicity of the counterion.