Zwitterionic Alternating Polymerization to Generate Semicrystalline and Recyclable Cyclic Polythiourethanes

Abstract

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.

Heterocycle/Heteroallene Ring‐Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

“…COS/aziridine ROCOP is also spontaneous through an activated monomer mechanism [234] . Using COS pressures of 10 to 20 MPa results in the formation of polymers with molar masses up to 15 kg mol −1 within 2 hours at room temperature [232, 233] . The highly alternating polymers were macrocyclic, as determined by MALDI‐TOF mass spectrometry, and were cleanly depolymerized at 200 °C into the five‐membered cyclic thiourethane.…”

Precisely Alternating Copolymerization of Episulfides and Isothiocyanates: A Practical Route to Construct Sulfur-Rich Polymers

“…The seeking of an innovative and reliable methodology for constructing sulfur-rich macromolecules has become one of the prevailing tendencies in polymer science. First, the construction of sulfur-containing polymers is deemed as a potential solution to deal with the huge sulfur production (80 million tons per year) that is being generated every day in the worldwide petroleum refineries. , Second, the introduction of sulfur elements into polymer backbones can empower the material with intriguing performance, for example, metal adsorption, − high refractive index, − complete recyclability, − and special electric characters. − …”

Chemically recyclable polymer materials: polymerization and depolymerization cycles

“…In addition to the epoxy examples above, in 2020, Luo and Darensbourg also reported a catalystfree zwitterionic alternating copolymerization of COS and N-alkyl aziridines (Scheme 1b). 53 This elegant copolymerization resulted in semicrystalline polythiourethane polymers with perfect alternating linkages (>99%). And more interestingly, these copolymers could be quantitatively recycled into five-membered N-substituted cyclic thiourethanes when heated at 250 °C via thermal recyclability.…”