Measurement of transfer coefficients to monomer for n-butyl methacrylate by molecular weight distributions from emulsion polymerization

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 the analysis of molecular weight distributions obtained by seeded emulsion polymerization under conditions such that chain transfer to monomer is the dominant chain-stopping event. Measurements between 40 and 70°C gave data fitting an Arrhenius-type relationship with exponential factor factor EA=30900±4500 J-mol⁻¹ and pre-exponential factor log A=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, suggesting that there is more hindrance for chain transfer to monomer for BMA than for either MMA or BA.