Zwitterionic Alternating Polymerization to Generate Semicrystalline and Recyclable Cyclic Polythiourethanes

摘要

Synthesis of cyclic, semicrystalline, and recyclable polythiourethanes was realized via the catalyst-free zwitterionic alternating copolymerization of N-alkyl aziridines with carbonyl sulfide (COS) under mild conditions. The copolymerization proceeded efficiently at room temperature and generated copolymers with fully alternating linkages in more than 99% selectivity in 5 min under solvent-free conditions. Notably, the copolymers are typical semicrystalline thermoplastics with melting temperatures up to 137 degrees C (n-butyl-substituted) or 170 degrees C (ethylsubstituted). The resulting polythiourethanes are predominantly cyclic as evidenced by H-1 NMR and MALDI-TOF mass spectroscopies. Remarkably, the cyclic copolymers could be recycled into N-substituted cyclic thiourethanes in quantitative yield by heating at 250 degrees C for 2 h.