EFFECT OF REACTION MEDIUM ON THE IONIZING RADIATION-INITIATED CATIONIC COPOLYMERIZATION OF STYRENE DERIVATIVES

The influence of reaction medium polarity on the ionizing radiation-in itiated copolymerization of styrene derivatives involving unpaired car bocations is examined. In the copolymerization of nonpolar monomers su ch as p-CH3styrene/styrene, a small effect consistent with that predic ted by Laidler-Eyring theory is found. In the copolymerization of nonp olar/polar monomer pairs such as p-CH3styrene/p-Clstyrene and styrene/ p-Clstyrene, any such effect is masked by specific solvation phenomena . A competition between such phenomena appears to exist, in which the different cations are dominated by different interactions. The p-Clsty ryl cation appears to undergo strong intramolecular complexation with the penultimate aromatic ring in nonpolar conditions; thus, this catio n displays increased selectivity toward monomers best able to disrupt the complex. The p-CH(3)styryl and styryl cations do not appear to be subject to such strong complexation; thus, in nonpolar solvent, their selectivity tends towards monomers with the highest cation-solvating a bility. The differing copolymerization behavior of the p-Clstyryl cati on is consistent with the findings of previous investigations of the e ffect of reaction medium on chain transfer with these monomers. (C) 19 95 John Wiley & Sons, Inc.