Abstract
Here we demonstrate the synthesis of cyclic polyacetylene (c-PA), or [∞]annulene, via homogeneous tungsten-catalysed polymerization of acetylene. Unique to the cyclic structure and evidence for its topology, the c-PA contains >99% trans double bonds, even when synthesized at −94 °C. High activity with low catalyst loadings allows for the synthesis of temporarily soluble c-PA, thus opening the opportunity to derivatize the polymer in solution. Absolute evidence for the cyclic topology comes from atomic force microscopy images of bottlebrush derivatives generated from soluble c-PA. Now available in its cyclic form, initial characterization studies are presented to elucidate the topological differences compared with traditionally synthesized linear polyacetylene. One advantage to the synthesis of c-PA is the direct synthesis of the trans–transoid isomer. Low defect concentrations, low soliton concentration, and relatively high conjugation lengths are characteristics of c-PA. Efficient catalysis permits the rapid synthesis of lustrous flexible thin films of c-PA, and when doped with I2, they are highly conductive (398 (±76) Ω−1 cm−1).

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All relevant data are provided in the figures, table and Supplementary Information.
Change history
14 September 2021
A Correction to this paper has been published: https://doi.org/10.1038/s41557-021-00809-9
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Acknowledgements
A portion of this work was performed in the McKnight Brain Institute at the National High Magnetic Field Laboratory’s Advanced Magnetic Resonance Imaging and Spectroscopy (AMRIS) Facility. The assistance from A. Mehta in the collection of the solid-state NMR data is gratefully acknowledged. D. Wei and J. Huang are acknowledged for assisting in the acquisition of diffuse-reflectance UV–vis spectra. This material is based on work supported by the National Science Foundation CHE-1808234. The solid-state NMR study was supported by National Science Foundation Cooperative Agreement DMR-1644779 and the State of Florida. The NMR spectrometer used to acquire the solid-state NMR spectra was funded, in part, by National Institutes of Health award S10RR031637. The MAS-DNP instrument at NHMFL is supported by the NIH P41 GM122698 and NIH S10 OD018519 grants.
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Z.M. synthesized c-PA and l-PA in all forms, characterized c-PA and l-PA with IR, Raman, CP-MAS 13C NMR and EPR, performed the cryogenic UV–vis monitoring the synthesis of temporarily soluble c-PA, synthesized and obtained the AFM images of cyclic bottlebrushes from temporarily soluble c-PA, and studied the conductivities of c-PA before and after doping with I2. S.A.G. synthesized c-PA, characterized c-PA with IR and studied its conductivity. C.R.B. studied the CP-MAS 13C NMR of c-PA and l-PA. C.E. provided data analysis and preliminary computational modelling of 13C NMR data. F.M.-V. performed MAS-DNP 13C NMR experiments. The manuscript was written with contributions from all authors. All authors have given approval to the final version of the manuscript. A.S.V. and B.S.S. directed the research.
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The authors and UF Research Foundation Inc. have filed patents related to this subject matter. PCT Patent Application No. PCT/US21/17916.
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Supplementary Figs. 1–25, Discussion and Tables 1–6.
Supplementary Video 1
This video depicts the colour change during the polymerization of dilute acetylene THF solution with catalyst 1.
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Miao, Z., Gonsales, S.A., Ehm, C. et al. Cyclic polyacetylene. Nat. Chem. 13, 792–799 (2021). https://doi.org/10.1038/s41557-021-00713-2
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