Visible-Light Initiated Thiol-Michael Addition Photopolymerization Reactions.

A visible-light base generating system was successfully employed in catalyzing the thiol-Michael addition reaction to yield cross-linked polymers from a stoichiometric mixture of model thiol and vinyl monomers. Implementation of the radical inhibitor TEMPO with a combination of a photosensitizer (isopropylthioxanthone, ITX) and a photobase generator (triazabicyclodecene tetraphenylborate, TBD·HBPh) resulted in suppression of radical mediated side reactions and provided stoichiometric and complete conversion of both thiol and vinyl functional groups. The new initiating system acts as an efficient visible-light photobase generator that improves the orthogonality of the thiol-Michael addition with respect to off-stoichiometric radical thiol-vinyl addition/vinyl chain reactions. This approach opens up a variety of possibilities for base-catalyzed reactions in multiple applications such as coatings and biomaterials that require biocompatible, environmentally friendly, and low-energy visible-light initiation.