EFFECTS OF SOLVENT ON MODEL COPOLYMERIZATION REACTIONS - A C-13-NMR STUDY

Relative reactivities of methyl methacrylate (MMA) styrene and vinyl a cetate (VAc) towards the 2-methyl-2-(methoxycarbonyl)ethyl (1) and cya noisopropyl (2) radicals have been determined in three solvents (benze ne, ethyl acetate and methanol). The experiments involved C-13-NMR ana lysis of the C-13-labelled end-groups of copolymers formed with either azo-bis-(methylisobutyrate-alpha-C-13) or azo-bis-(isobutyronitrile-a lpha-C-13) as initiator. Relative reactivities of styrene vs MMA and M MA vs VAc were the same in benzene and ethyl acetate. Use of methanol as solvent was found to enhance slightly the relative reactivity of st yrene vs MMA towards both radicals. The significance of these results is discussed in relation to the mechanism by which solvents modify rea ctivity ratios in radical copolymerization.