RAFT-mediated emulsion polymerization of styrene with a thermoresponsive MacroCTA

Heterogeneous RAFT polymerization is an attractive ‘living’ radical polymerization technique to control not only the molecular weight distribution but also the particles size distribution. Here, we demonstrate the use of a thermoresponsive RAFT macro chain transfer agent (MacroCTA) to form seed particles for the chain extension of styrene to form block copolymer latex particles. By incorporating a few styrene units into the MacroCTA, the polymerizations become faster, producing both narrow particle size and molecular weight distributions. This is due to the ‘superswelling effect’, in which all the seed particles swell with monomer and nucleated at the same time. The resulting latex particles could then be transformed into a variety of nanostructures by cooling below the lower critical solution temperature of the thermoresponsive block in the presence of a plasticizer for polystyrene. The dominant structure was cylindrical worms with the observation of other structures including jelly fish and the rare disc. Cooling under ultrasound produced either vesicles or cauliflower structures. The work demonstrated that utilizing the ‘superswelling effect’, control over the rate, and molecular weight and particle size distributions could be obtained, providing design parameters to construct new nanostructures.