Thiocarbonyls: synthesis of alternative monomers for biodegradable vinyl copolymers Sade Adamolekun , Nathaniel M. Bingham, Peter J. Roth University of Surrey, UK
It is an established fact that the C-C bonds in the backbone of vinyl polymers inhibit/prevent their degradation with a resultant high level of environmental pollution and limits to the alternative use of such polymers in biomedicine. Notwithstanding, copolymerization of this class of materials with other functional groups has been reported to produce biocompatible materials with inherent degradability fueling the application of polymers in tissue engineering, surgical sutures, implants and drug delivery. Such methods involve cyclic monomers that undergo radical ring-opening polymerization. Herein, non-cyclic monomers containing thiocarbonyl groups are investigated as comonomers in vinyl polymerizations. The goal is to identify suitable monomers that polymerize through the C=S bond (like a vinyl monomer) and introduce heteroatoms into the backbone. Three thionoesters and three thioamides have been successfully synthesized by one-step thionation of their respective oxoester/ amide precursors using Lawesson’s reagent. Thioamides were obtained in excellent yields as opposed to their thionoester counterparts (50-12% yields). Copolymerization of these compounds with vinyl acetate (VA), styrene (sty), methyl acrylate (MA), and methyl methacrylate (MMA) were attempted using AIBN at 70 °C in acetonitrile. All of the trialled thiocarbonyls were found to be spectators in the homopolymerization of sty, MA, and MMA. Trifluoro- N , N -dimethyl thioacetamide and methyl thionobenzoate were found to retard and inhibit the polymerization of vinyl acetate, respectively. Thioamides show more promising features than thionoesters in the incorporation which could be attributed to more energetically favourable formation of a C=O group leading to greater probability of β-scission than in thioamides. Watanabe and Kamigaito 1 recently reported a successful incorporation of some thioamides which further buttress the feasibility of this project. However, alternative reaction conditions are being explore to establish this. References 1. Watanabe, H.; Kamigaito, M., Direct Radical Copolymerizations of Thioamides To Generate Vinyl Polymers with Degradable Thioether Bonds in the Backbones. Journal of the American Chemical Society 2023, 145 (20), 10948-10953.
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© The Author(s), 2023
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