Surfactant-Free, Controlled/Living Radical Emulsion Polymerization in Batch Conditions Using a Low Molar Mass, Surface-Active Reversible Addition-Fragmentation Chain-Transfer (RAFT) Agent

Abstract

The purpose of this paper was to study the application of a surface-active trithiocarbonate RAFT agent, the 2-(dodecylthiocarbonothioylthio)-2-methylpropanoic acid, sodium salt (TTCA) in surfactant-free, ab initio, batch emulsion polymerization. Because of the highly water-soluble character of the leaving group favoring exit from the micelles or the particles over reinitiation, the polymerization of styrene was completely inhibited. In contrast, the polymerization of n-butyl methacrylate was fast and led to small, stable particles, demonstrating the good stabilizing efficiency of TTCA. However, the control over molar mass was not effective, as homopolymers with high molar mass were formed. This was related to the inappropriate leaving/initiating group and low chain transfer constant of the RAFT agent in the free-radical polymerization of methacrylic esters and was also observed in bulk. This poor efficiency was overcome by copolymerizing n-butyl methacrylate with a low percentage of styrene or n-butyl acrylate. In this case, the bulk copolymerization led to controlled copolymers with predicted molar mass and narrow molar mass distribution and the chain transfer efficiency was similarly high in surfactant-free emulsion polymerization. The good colloidal characteristics of the latexes with the stabilizing group attached at the chain-end were maintained, leading to autostabilized latexes with small particle diameter, below 150 nm. This work is the first example of the direct and efficient use of a surface-active, low molar mass, RAFT agent in emulsifier-free, batch emulsion polymerization, leading simultaneously to a good control over molar mass and narrow molar mass distribution, together with good colloidal properties.