Synthesis and Thiol-ene Photopolymerization of (meth)allyl-terminated Polysulfides

Mark R. Brei, University of Southern Mississippi
Brian R. Donovan, University of Southern Mississippi
Derek L. Patton, University of Southern Mississippi
Robson F. Storey, University of Southern Mississippi


Thiol-terminated polysulfides (PS) are cured by mixing with an oxidant, resulting in limited shelf- and/or pot-life, depending on whether formulated as a one- or two-component system. Mixtures of thiol- and alkene-terminated polysulfides offer the potential for an on-demand curing process through thiol-ene photopolymerization. Thiol end groups of commercial polysulfides, PS-1 (1000 g/mol) and PS-2 (3000 g/mol), were converted to alkene by reaction with (meth)allyl bromide. Photopolymerizations were performed by irradiating films of equimolar thiol:ene mixtures at 320-500 nm (30 mW/cm(2)) in the presence of 5 wt % 2,2-dimethoxy-2-phenyl-acetophenone (DMPA). Reaction kinetics were measured using real-time FTIR by monitoring absorbances at 3075 cm(-1) (alkene) or 2550 cm(-1) (thiol). In the absence of any reactive diluent, mixtures of thiol and alkene polysulfides failed to gel notwithstanding high reaction conversion (>90%). Partial or total replacement of the thiol polysulfide component with pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) yielded solid elastomeric films and ultimate reaction conversions of 80-96% after 5 min irradiation. Crosshatch adhesion measured on glass, aluminum, and steel was very poor (0B) for (meth)allyl PS-1/PETMP and poor (2B) for (meth)allyl PS-2/PETMP without adhesion promoters. (3-Mercaptopropyl)trimethoxysilane (1 wt %) significantly improved adhesion of (meth)allyl PS-2/PETMP on all substrates (4B) but yielded no improvement for (meth)allyl-terminated PS-1/PETMP. (c) 2017 Wiley Periodicals, Inc.