Cooperative taming of CS2/oxetane copolymerisation: Consequences of main-chain sulfuration on polymer properties and catalysis

Abstract

CS2 promises easy access to degradable sulfur-rich polymers and insights into how main-group derivatisation affects polymer formation and properties, though its ring-opening copolymerisation is plagued by low linkage selectivity and small-molecule by-products. We demonstrate that a cooperative Cr(III)/K catalyst selectively delivers poly(dithiocarbonates) from CS2 and oxetanes while state-of-the-art strategies produce linkage scrambled polymers and heterocyclic by-products. The formal introduction of sulfur centres into the parent polycarbonates results in a net shift of the polymerisation equilibrium towards, and therefore facilitating, depolymerisation. During copolymerisation however the catalyst enables near quantitative generation of the metastable polymers in high sequence selectivity by limiting the lifetime of alkoxide intermediates. Furthermore, linkage selectivity is key to obtain semi-crystalline materials that can be moulded into self-standing objects. Our report demonstrates the potential of cooperative catalysis to produce previously inaccessible main-group rich materials with beneficial chemical and physical properties

Metal-Free Alternating Copolymerization of CS2 and Oxetane

“…Another TEB-activated oxetane was subsequently attacked by IN3 via TS6 (9.6 kcal/ mol), leading to the success of chain growth. Compared to the previously reported metal catalysts, 40,66 TEB possesses weaker Lewis acidity, resulting in a more controllable polymerization process.…”

“…60−65 During the preparation of this work, Plajer and co-workers reported the synthesis of polythiocarbonate with up to 96 mol % L1 units from CS 2 and oxetane copolymerization using the state-of-the-art bimetal Cr(III)/K catalyst, which is published in the preprint. 66 The turnover number of the catalyst was up to 7300 and the M n of the copolymer was up to 100 kDa. The catalyst also achieved a well control over monomer sequence from the copolymerization of oxetane with cyclic thiocarbonate or isothiocyanate.…”

“…The catalyst also achieved a well control over monomer sequence from the copolymerization of oxetane with cyclic thiocarbonate or isothiocyanate. 66 Here, we sought to use alkyl borane instead of metal catalysts as a LA for the copolymerization of CS 2 with TMO. Of interest, organocatalyzed copolymerization exhibits high sequence selectivity, yielding polythiocarbonate with 98 mol % L1 unit, which was inaccessible by previous research.…”