Ultrafine Nanolatexes Made via Monomer-Starved Semicontinuous Emulsion Polymerization in the Presence of Water-Soluble Chain Transfer Agents

Ideal chain transfer agents are usually water insoluble as they do not affect the kinetics of polymerisation reactions occurring in the water phase. Water-soluble chain transfer agents act non-ideally by easily crossing the water phase and affecting the kinetics of polymerisation including nucleation. In this research, a partially water-soluble chain transfer agent (CTA), 2-Butanethiol, was used in the monomer-starved semicontinuous emulsion polymerisation of styrene as a means to affect the kinetics of water phase and synthesise ultrafine nanolatexes. Batch emulsion polymerisations were also carried out for comparison. In the batch process, the termination of chain transferred radicals in the water phase was found to be quite dominant, resulting in the formation of large polymer particles with polydisperse molecular weights and slow rate of reaction. By contrast, for the semicontinuous process, the application of the CTA reduced the average size of particles, by enhancing the rate of nucleation via increasing the rate of radical entry into micelles, and provided a good controllability over molecular weight distribution as well as the rate of polymerisation.