Monodisperse, micron-sized reactive low molar mass polymer microspheres by two-stage living radical dispersion polymerization of styrene

Living/controlled radical dispersion polymerization of styrene was carried out in ethanol and in ethanol-water mixtures in the presence of perfluorohexyl iodide (C6F13I, 2-5 wt % based on styrene) as a degenerative chain transfer (DCT) agent or 1-cyano-1-methylpropyl dithiobenzoate (CMPDB, 0.5 and 1.0 mol % based on styrene) as a reversible addition-fragmentation chain transfer (RAFT) agent. These reagents disrupt the nucleation stage of particle formation when present at the start of the reaction. If their addition is delayed until the nucleation stage is complete, the reaction acquires the characteristics of a living/controlled radical polymerization: M-n increases linearly with the monomer conversion, and the molar mass distribution is much narrower (minimal M-w/M-n: 1.2) than polystyrene prepared without C6F13I or CMPDB. For reactions in ethanol, at low molar mass, the particles formed have a broad size distribution as a consequence of the solubility of the polymer at the reaction temperature, followed by precipitation upon cooling. When the reactions were run in a more polar medium (95 wt % aqueous ethanol), the polymer molecules precipitated as they were formed and were absorbed by the existing particles in the solution. The particles formed had an average diameter in the range 1-3 Am with a very narrow size distribution (CV < 1%). The polymer chains in these particles are reactive and chain-extendible.