Successful Use of RAFT Techniques in Seeded Emulsion Polymerization of Styrene: Living Character, RAFT Agent Transport, and Rate of Polymerization

Abstract

Reversible addition−fragmentation chain transfer (RAFT) polymerization techniques are successfully used to control molecular weight and polydispersity in the seeded emulsion polymerization of styrene. A novel technique was used to assist the transport into the seed particles of a RAFT agent that is of very low water solubility, ensuring the RAFT agent was localized in the particle phase. The polymer produced in these experiments was seen to have low molecular weight polydispersity (1.1 < M̄ w / M̄ n < 1.4), and the molecular weight could be controlled by the amount of RAFT agent used. The procedure permitted living polymerization to be performed in an emulsion polymerization system. Importantly, the RAFT agent had no adverse effect on latex stability, and unusual amounts of coagulum were not observed. Reductions in the rate of polymerization (measured by dilatometry) were observed along with significant inhibition periods, for which possible explanations and remedies are discussed. This appears to be the first instance where good living character has been demonstrated in a true emulsion polymerization of styrene while maintaining good colloidal stability.