Model copolymerization reactions. Evidence against concerted complex addition in reactions of simple alkyl radicals with N-phenylmaleimide and donor olefins

Reductive demercuration was used to generate the 1-butyl and benzyl radicals in mixtures of N-phenylmaleimide (NPM) and either of the donor olefins styrene or 2-chloroethyl vinyl ether (CEVE). In each case, the major products of the reaction were derived from simple addition of the radical to NPM followed by transfer of a hydrogen atom to the initial adduct. Careful mass balances on NPM showed that mechanisms other than simple addition did not constitute important pathways for monomer consumption. These results argue against mechanistic schemes for radical copolymerization in which 1:l monomer complexes add in a concerted manner to growing macroradicals.