Relative reactivity of chloroprene and methyl methacrylate toward initiator radicals

The relative rates of addition of chloroprene (CP) and methyl methacrylate (MMA) toward small model radicals structurally similar to the poly(MMA), poly(methacrylonitrile) and poly(styrene) radical was investigated following the method of Bevington and Huckerby [J Polym Sci Polym Chem 20 (1982) 2655]. Results indicate that these small radicals are significantly more selective toward CP than the corresponding polymer radicals, consistent with earlier reports that penultimate unit effects may be important in the copolymerisation of CP with MMA and styrene. As previous investigations of substituted dienes by the end-group method have given similar results for polymer radicals and small model radicals, this may constitute evidence for a penultimate unit effect that is predominantly electronic rather than steric in origin.