Mass transfer effects in emulsion polymerization systems. I. Diffusional behavior of chain transfer agents in the emulsion polymerization of styrene

On the basis of the so‐called two‐films theory for mass transfer, a mathematical model for transfer of chain transfer agents from monomer droplets to polymer particles, where chain transfer agent molecules are consumed by the chain transfer reaction, is developed for an emulsion polymerization system. It is shown by the model that the concentration of chain transfer agent in the polymer particles during the polymerization is decreased to a value much less than that which would be attained if thermodynamic equilibrium for chain transfer agent were reached between the polymer particles and the monomer droplets, due mainly to the resistance to transfer of chain transfer agent molecules across the diffusion films at the interface between the monomer droplets and the water phase. The validity and utility of the model developed for predicting the diffusion and consumption rates for chain transfer agent are demonstrated experimentally using five normal aliphatic mercaptans from n‐C7 to n‐C12 as chain transfer agents in the seeded emulsion polymerization of styrene.