Polymer Microspheres Prepared by Water-Borne Thiol-Ene Suspension Photopolymerization

Thiol-ene polymerizations are shown to be possible in a water-borne suspension-like photopolymerization and yield spherical particles that have diameters in the range of submicrometers to hundreds of micrometers. This is the first report of such colloidal thiol-ene polymerizations. Thiol-ene polymerization offers unique conditions not commonly associated with a water-borne polymerization including a step-growth polymerization mechanism along with photoinitiation under ambient conditions. Example polymerizations of a triene, 3,5-triallyl-1,3,5-triazine-2,4,6 (1N,3H,5H)-trione (TTT), and a tetrathiol, pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), with the photoinitiator 1-hydroxycyclohexyl phenyl ketone, surfactant sodium dodecyl sulfate (SDS), and a cosolvent (chloroform or toluene) are discussed. Various experimental parameters were examined such as surfactant concentration, homogenization energy, cosolvent species, and cosolvent amount in order to develop an understanding of the mechanism of microsphere formation. It is demonstrated that particle size is dependent on homogenization energy, with greater mechanical shear yielding smaller particles. In addition, higher concentrations of surfactant or solvent also produced smaller spherical particles. These observations lead to the conclusion that the particles are formed via a suspension-like polymerization.