Non-isocyanate Polythiourethane Network from Biowaste: Achieving Circularity via Multidimensional Chemical Recycling with Valuable Small-Molecule Recovery and Reprocessability by Understanding the Dynamic Chemistry

Abstract

We studied and established the dual nature of non-isocyanate polythiourethane (NIPTU) dynamic chemistry and capitalized on our understanding to achieve multidimensional chemical recycling of a cross-linked NIPTU, also known as poly(mercapto-thiourethane). This NIPTU chemical recycling includes the first demonstration of recovery of valuable small molecules in addition to reprocessability with full cross-link density recovery. In particular, we performed the first investigation of NIPTU dynamic chemistry using small-molecule analogues. We identified two types of dynamic chemistry: reversible cyclic thiocarbonate aminolysis, where the non-isocyanate thiourethane (NITU) groups in NIPTU reversibly dissociate into cyclic thiocarbonates and amines, and trans(thio)carbamoylation, where the thionourethane linkages within the NITU groups undergo exchange reactions with alcohol. We synthesized a renewable glycerol-based NIPTU (GNIPTU) with a high biowaste-derivable content. Capitalizing on trans(thio)carbamoylation, we recovered pure di(thiocarbamate) small molecules with a 94 mol % yield, one of the highest yields among reported studies of chemical recycling of polymers. The GNIPTU network exhibited full property recovery after reprocessing, providing another effective method of chemical recycling. With robust properties, high biowaste-derivable content, the capability to undergo multidimensional chemical recycling with excellent small-molecule recovery, and full reprocessability, the GNIPTU network exemplifies how low-cost, renewable, non-isocyanate polyurethane-like materials can be developed with both high-performance characteristics and the potential to contribute meaningfully to polymer circularity.