Alternating Chain Growth Copolymerization of Isothiocyanates and Epoxides

• Published in: Macromolecules Vol. 54; no. 22; pp. 10529 - 10536
• Main Authors: Song, Lidao, Liu, Mingqi, You, Donglei, Wei, Wei, Xiong, Huiming
• Format: Journal Article
• Language: English
• Published: American Chemical Society 23.11.2021
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.1c01561

A class of heteroatom polymers through anionic chain growth copolymerization of epoxides and isothiocyanates has been successfully obtained under mild conditions via initiation by a simple salt of lithium alkoxide. The resulting polymers have characteristics of controlled molecular weights and low dispersity with a well-defined backbone of carbonimidothioate repeat units (-OC­(=N)­S-) at 100% alternating degree, which have been confirmed in the 1H-13C heteronuclear multiple bond correlation NMR spectrum and mass spectrum. Side reactions have been greatly suppressed in the copolymerization, and no more than 5% cyclic small molecular byproducts have been produced. We have revealed the special role of lithium bonds in regulating the alternating copolymerization of these two types of monomers, which are involved in activating isothiocyanates as well as binding the incoming monomers to the growing chain ends due to the especial coordination capability of lithium ions to multiple nucleophilic sites. The proposed mechanism of the alternating copolymerization process is supported by density functional theory calculations. Moreover, the copolymerization exhibits first-order kinetics with respect to the monomers and a quasi-living feature. Our strategy is expected to shed light on the incorporation of different types of cumulated double bonds as comonomers into polymer backbones, and the high availability of epoxides and isothiocyanates of various substitutions will forge the development of such kinds of heteropolymers.