Cationic ring-opening polymerisation of a Thionolactone to produce recyclable materials Swarnali Neogi, Qamar-un-Nisa, Kyle Collins, Nathaniel M. Bingham, Peter J. Roth University of Surrey, UK Vinyl polymers are not degradable because they have a C–C backbone which makes them difficult to recycle chemically. Although vinyl polymers are versatile and have important applications, their non-degradability limits current and emerging applications. Thionolactones are a class of monomer that can introduce labile linkages in the backbone of vinyl polymers by ring-opening polymerisation (ROP). In this work, the cationic homopolymerisation (via cationic ring-opening polymerization, CROP) of the thionolactone monomer dibenzo[c,e] oxepine-5(7H)-thione (DOT) will be presented. Several cationic initiators have been found to successfully initiate the CROP of DOT. The mechanism is presumed to involve a benzylic cation after ring-opening. The addition of this positively charged species onto the thionolactone functional group [-C(=S)O-] of another DOT molecule produces cleavable thioester groups [-S(C=O)-] in each repeat unit of the polymer. Analysis of the products by nuclear magnetic resonance (NMR) spectroscopy indicated good conversion rates (>90%) and confirmed the expected DOT–DOT linkages through degradable thioesters. These cationically made homopolymers (polyDOT) can be easily and completely degraded into small molecules through different methods. Specifically, thiolysis in the presence of base causes polyDOT to depolymerise at room temperature to produce dibenzo[c,e]thiepan- 5(7H)-one (DTO) as the single product. This can be promising towards the scope of recycling and reusability of such materials. References 1. Bingham, N. M.; Roth, P. J. Degradable vinyl copolymers through thiocarbonyl addition-ring-opening (TARO) polymerization. Chem. Commun. 2019, 55, 55−58. 2. Spick, M. P.; Bingham, N. M.; Li, Y.; de Jesus, J.; Costa, C.; Bailey, M. J.; Roth, P. J. Fully Degradable Thioester-Functional Homo- and Alternating Copolymers Prepared through Thiocarbonyl Addition-Ring-Opening RAFT Radical Polymerization. Macromolecules 2020, 53, 539−547. 3. Kiel, G. R.; Lundberg, D. J.; Prince, E.; Husted, K. E. L.; Johnson, A. M.; Lensch, V.; Li, S.; Shieh, P.; Johnson, J. A., Cleavable Comonomers for Chemically Recyclable Polystyrene: A General Approach to Vinyl Polymer Circularity. J Am Chem Soc 2022, 144 (28), 12979-12988. 4. Sanda, F.; Jirakanjana, D.; Hitomi, M.; Endo, T., Cationic ring-opening polymerization of ϵ-thionocaprolactone: Selective formation of polythioester. J. Polym. Sci., Part A: Polym. Chem. 2000, 38 (22), 4057.
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