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 °C (n-butyl-substituted) or 170 °C (ethyl-substituted). The resulting polythiourethanes are predominantly cyclic as evidenced by ¹H 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 °C for 2 h.

中文翻译：

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两性离子交替聚合生成半结晶和可回收的环状聚硫氨酯

在温和条件下，通过N-烷基氮丙啶与羰基硫 (COS)的无催化剂两性离子交替共聚，实现了环状、半结晶和可回收的聚硫氨酯的合成。共聚在室温下有效进行，并在无溶剂条件下在 5 分钟内以超过 99% 的选择性生成具有完全交替键的共聚物。值得注意的是，这些共聚物是典型的半结晶热塑性塑料，熔融温度高达 137 °C（正丁基取代）或 170 °C（乙基取代）。所得聚硫氨酯主要是环状的，如¹H NMR和MALDI-TOF质谱。值得注意的是，通过在 250°C 加热 2 小时，环状共聚物可以定量回收成 N-取代的环状硫代氨基甲酸乙酯。