Abstract
The selective synthesis of ultrahigh-molar-mass (UHMM, >2 million Da) cyclic polymers is challenging as an exceptional degree of spatiotemporal control is required to overcome the possible undesired reactions that can compete with the desired intramolecular cyclization. Here we present a counterintuitive synthetic methodology for cyclic polymers, represented here by polythioesters, which proceeds via superbase-mediated ring-opening polymerization of gem-dimethylated thiopropiolactone, followed by macromolecular cyclization triggered by protic quenching. This proton-triggered linear-to-cyclic topological transformation enables selective, linear polymer-like access to desired cyclic polythioesters, including those with UHMM surpassing 2 MDa. In addition, this method eliminates the need for stringent conditions such as high dilution to prevent or suppress linear polymer contaminants and presents the opposite scenario in which protic-free conditions are required to prevent cyclic polymer formation, which is capitalized to produce cyclic polymers on demand. Furthermore, such UHMM cyclic polythioester exhibits not only much enhanced thermostability and mechanical toughness, but it can also be quantitatively recycled back to monomer under mild conditions due to its gem-disubstitution.
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Acknowledgements
Funding was provided by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Materials and Manufacturing Technologies Office (AMMTO) and Bioenergy Technologies Office (BETO). This work was performed as part of the Bio-Optimized Technologies to keep Thermoplastics out of Landfills and the Environment (BOTTLE) Consortium and was supported by AMMTO and BETO under Contract DE-AC36-08GO28308 with the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC. The BOTTLE Consortium includes members from Colorado State University. The work by L.T.R. and E.Y.-X.C. was supported by the US National Science Foundation (grant no. NSF-2305058). We thank R. R. Gowda for dn/dc measurements.
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E.Y.-X.C. conceived the project and directed the research. L.Z., L.T.R., C.S. and E.C.Q. designed and conducted experiments and analysed the results. L.Z. wrote the initial paper, L.T.R. and E.C.Q. contributed to subsequent versions. E.Y.-X.C. edited the initial and subsequent versions and reviewed the entire paper.
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E.Y.-X.C. and L.Z. are named inventors on a pending PCT/US patent application (2023/021512) submitted by Colorado State University, which covers chemically circular polymers. The other authors declare no competing interests.
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Zhou, L., Reilly, L.T., Shi, C. et al. Proton-triggered topological transformation in superbase-mediated selective polymerization enables access to ultrahigh-molar-mass cyclic polymers. Nat. Chem. (2024). https://doi.org/10.1038/s41557-024-01511-2
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DOI: https://doi.org/10.1038/s41557-024-01511-2