Non-Isocyanate and Catalyst-Free Synthesis of a Recyclable Polythiourethane with Cyclic Structure

Polythiourethane is a promising heteroatom-containing polymeric material possessing outstanding properties such as high refractive index, biocompatibility, and good coordinating ability to heavy metal ions. However, examples of versatile polythiourethanes are relatively scarce as a result of the limited methods for their synthesis. Herein, we report an efficient non-isocyanate and catalyst-free strategy to synthesize polythiourethane from the highly alternating and regioselective copolymerization of carbonyl sulfide (COS) and 2-methyl aziridine. The copolymerization proceeded efficiently at room temperature and afforded copolymer in 95% selectivity and molecular weight of 15.2 kg/mol in 2 h. Furthermore, the reaction was efficient even at 1 atm of COS at room temperature. Remarkably, the copolymer possessed a cyclic topology, and it could be completely recycled into cyclic thiourethane by simply heating the bulk materials at 200 °C for 1.5 h. The copolymer was applied as a heavy metal absorption and recovery agent; lead ions in aqueous solution were adsorbed by the copolymer, and both were eventually separated and recovered in the form of lead compounds and cyclic thiourethanes, respectively. Hence, this study provides a sustainable and atom-economical method for synthesizing polythiourethane and a green method to recover hazardous metals with minimal waste and VOC emission.