Measurement of Transfer Constant for Butyl Acrylate Free-Radical Polymerization

Arrhenius parameters for the transfer constant to monomer (C M) for the free-radical polymerization of butyl acrylate (BA) are determined by a combination of techniques. A seeded emulsion polymerization with conditions designed so that “zero−one” kinetics are obeyed, i.e., where entry of a radical into a particle causes instantaneous termination, such that transfer to monomer can be shown to be the dominant chain-stopping event. The seed comprised small polystyrene particles, which reduces the likelihood of chain transfer to polymer provided the polymer:monomer ratio is sufficiently low. Since the dominant chain-stopping events are then entry and transfer to monomer, C M can then be obtained from the number molecular weight distribution for different initiator concentrations and conversions and isolating the component due to transfer to monomer. The transfer constant so obtained, over the temperature range 50−72 °C, fits C M = (0.016 ± 0.003) exp(−(15.2 ± 0.6) kJ mol-1/RT).