Radical mediated thiol-ene/yne dispersion polymerizations

Abstract

Abstract We report the synthesis of polymeric particles using radical mediated step-growth thiol-ene and thiol-yne ‘click’ dispersion polymerizations in alcoholic solvents. Various alkene, alkyne and thiol monomers were used, and thermal, photo- or redox initiation methods were all shown to be effective means to initiate polymerization. Polymer particles typically were formed with diameters in the range of several hundred nanometers, with narrow size distributions though broader than typical free-radical chain-growth dispersion polymerizations. Photoinitiation yielded the smallest sizes due to the rapid nucleation of particles as compared to redox and thermal initiation methods. Reaction kinetics were monitored by FT-IR spectroscopy for aliquot samples taken at various reaction durations. The reaction achieved full conversion in photoinitiated systems within five minutes, while it took three hours for both thermal and redox initiation to be completed. The effects of polymerization conditions on particle size particularly the impact of monomer, stabilizer, and initiator concentrations were studied. Generally, average particle size increased with higher monomer concentration and decreased with additional stabilizer or initiator. Combinations of monomers with varying number of functional groups were investigated to form particles of various mechanical and physical behavior, including both linear and crosslinked systems.