Photo-oxidative cross-linking of thiol polydimethylsiloxane co-polymers via disulfide formation

Abstract

The formation of disulfide linkages from thiol functionalities in polymeric materials can be used as a strategy for the preparation of degradable materials. Here we demonstrate the photo-oxidation of thiol functionalities into disulfide cross-links using a telluride catalyst and photo-generated singlet oxygen. We use blue light to produce reactive singlet oxygen from a solubilized porphyrin sensitizer that oxidizes the telluride pre-catalyst into an active state which oxidizes the thiol functionalities into disulfide groups. The kinetics of this process were studied using inline photo (UV)-rheology, with the rate of cross-linking dependant on the telluride concentration while the cross-linking onset depends on the rate of telluride oxidation. This procedure is used to photo-cross-link thiol-containing siloxane copolymers into elastic materials with mechanical elongations of between 70–420% depending on polymer composition. The disulfide cross-links can be degraded using organic reductants to revert the materials from an elastomeric solid back to a liquid.