Initiator-Free Thiol-Aldehyde Photo Polycondensation

Traditional photopolymerizations generally require an initiator for initiating the polymerization while few cases have created degradable chemical bonds. Moreover, the migration instability and cytotoxicity of photo initiators are posing issues to human health and the environment. In this work, we discovered an initiator-free photo polycondensation system (IFPPC) between polymercaptans and aldehyde monomers, producing elastic and high strength plastic materials with exchangeable and degradable dithioacetal groups. IFPPC proceeds through a radical mechanism and is applicable in producing linear polymers and crosslinked networks. Nano-composites can also be obtained via an organic solvent-free Pickering emulsion polymerization using cellulose nanofibers as the stabilizer. The dithioacetal groups afford excellent stability under hydrolytic conditions and repeated thermal processing of cross-linked polymers, while their cleavage in aqueous solution of salts (silver nitrate, zinc iodide, copper bromide, etc.) results in fast degradation for recovering the aldehyde monomer. This is a successful demonstration of producing recyclable and degradable plastics through photo irradiation while avoiding the problematic issues of photo initiators.