Emulsifier-Free Controlled Free-Radical Emulsion Polymerization of Styrene via RAFT Using Dibenzyltrithiocarbonate as a Chain Transfer Agent and Acrylic Acid as an Ionogenic Comonomer: Batch and Spontaneous Phase Inversion Processes

Abstract

Surfactant-free, batch emulsion polymerization of styrene was carried out in the presence of sodium acrylate as a comonomer and dibenzyltrithiocarbonate (DBTTC) as a reversible addition−fragmentation chain transfer (RAFT) agent. Very stable latex was recovered with narrow particle size distribution. Because of the low water-solubility of DBTTC, diffusion of the RAFT agent from the monomer droplets toward the polymer particles was slow, which did not allow a linear increase of molar mass with monomer conversion. However, Mn eventually reached the expected value and the final polymer chains could be extended, when the latex was used as a seed for a second polymerization step. To overcome the slow diffusion of the RAFT agent, a new process was proposed, based on a spontaneous phase inversion mechanism. The method relies upon a first bulk copolymerization of styrene and acrylic acid, followed by neutralization of the carboxylic acid moieties by the addition of a sodium hydroxide solution under gentle stirring...