Cyclic xanthates enable degradable vinyl copolymers with cleavable backbone structures

Radical thiocarbonyl addition-ring-opening (TARO) copolymerisation offers a promising route for incorporating weak linkages into vinyl-based polymers, enabling their controlled degradation. Expanding the scope of this method, researchers have developed a novel cyclic xanthate monomer, 4_H_-1,3-benzoxathiin-2-thione (BOT), which features an additional in-ring sulfur atom. The monomer was synthesised via reaction of 2-mercaptobenzyl alcohol with thiophosgene, avoiding thionation reactions commonly used for similar monomers.

BOT was polymerised using an AIBN-initiated radical mechanism, achieving a 37 % conversion rate. Importantly, approximately 75 mol% of the BOT units underwent ring-opening, forming dithiocarbonate repeat units alongside ring-retained dithioorthoester units. When copolymerised with N,N-dimethylacrylamide (DMA), BOT demonstrated quantitative ring-opening across copolymer compositions ranging from 2.5 mol% to 16 mol%. Reactivity ratios (_r_DMA = 2.73 and r_BOT = 0.04) indicate that BOT is less reactive than DMA, ensuring its uniform distribution throughout the copolymer matrix.

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Dual C–S bond cleavage enables efficient degradation

The dithiocarbonate repeat units introduced by BOT exhibited unique degradability via aminolysis and basic hydrolysis. Unlike conventional degradable monomers, these units feature two cleavable C–S bonds, allowing for complete degradation without retaining fragment end groups. This feature sets cyclic xanthates apart from other TARO monomers, such as thionolactones, which are prone to forming vinyl homopolymerisation products.

The findings highlight the potential of cyclic xanthates for creating environmentally friendly acrylamide copolymers. Their finely tunable degradability and compatibility with high-yield polymerisation processes make them an excellent choice for advanced polymer applications, including biomedical materials and sustainable packaging.

Source: Hepburn, K. S., & Roth, P. J. (2026). Degradable vinyl copolymers featuring backbone dithiocarbonates by radical copolymerisation of a cyclic xanthate. Polymer Chemistry. https://doi.org/10.1039/D5PY00805K

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