The advancement of soft materials relies heavily on innovation in polymerization reactions. Here, we discover alternating copolymerization of isothiocyanate (ITC) and epoxide which results in an unprecedented sulfur-containing polymer, polythioimidocarbonate (PTC). Provided with a simple two-component catalyst, i.e. Lewis pair consisting of triethylborane (Et3B) and excess phosphazene base (PB), the copolymerization starts from an alcohol and proceeds in a strictly alternating and highly chemoselective manner, yielding PTC with controlled molar mass and low dispersity, free of cyclic byproduct and ether linkages. The method applies well on a variety of ITCs and epoxides. It is also found with great excitement that the reaction on ITC is fully inhibited when the catalyst composition is inverted to have Et3B in excess, whilst homopolymerization of epoxide occurs selectively in this case. DFT calculation reveals that Et3B-alkoxide complexation is key to suppress back-biting reaction during the copolymerization ([Et3B] &lt; [PB]) and inhibit the copolymerization ([Et3B] &gt; [PB]). This unique “biased” feature is harnessed to develop a catalyst switch strategy for one-pot block copolymerization from the mixture of ITC and epoxide following either a copolymerization- or homopolymerization-first order, resulting in tailor-made PTC-polyether block copolymers with reversible sequence structures. On the other hand, sequence-selective terpolymerization occurs from a mixture of phthalic anhydride, ITC, and epoxide, allowing one-step synthesis of polyester-PTC block terpolymer. These results have highlighted the versatility of the method for exploring this uncharted area of polymers.

Simple and precision approach to polythioimidocarbonates and hybrid block copolymer derivatives

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.