1 Measurement of Transfer Coefficients to Monomer for n-Butyl Methacrylate by Molecular Weight Distributions from Emulsion Polymerization

Summary The average kinetic coefficient for chain transfer to monomer <ktr,M> in the free-radical polymerization of n-butyl methacrylate (BMA) has been determined by analysis of the molecular weight distributions obtained by seeded emulsion polymerization under conditions such that chain transfer to monomer is always the dominant chain-stopping event. Measurements were carried out at temperatures between 40ºC and 70ºC and consistent parameters obtained for chain transfer to BMA. The resulting data fitted an Arrhenius-type relationship provided by exponential factor EA = 30900±4500 J·mol–1 and pre-exponential factor logA = 3.45±0.15 The value for EA is comparable with published data for chain transfer to monomer from methyl methacrylate (MMA) and n-butyl acrylate (BA). The A value, however, is 1-3 orders of magnitude smaller. This suggests that there is more hindrance for chain transfer to monomer for BMA than for either methyl methacrylate (MMA) or n-butyl acrylate (BA) which may be explained by the extent of hindrance about the most probable site for hydrogen abstraction