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Precision copolymerization of CO2 and epoxides enabled by organoboron catalysts

Nature Synthesis volume 1, pages 892–901 (2022)Cite this article

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Abstract

Copolymerization of CO2 and epoxides is an industrially relevant means to alleviate anthropogenic carbon emissions and non-degradable plastic pollution. Despite recent advances, few studies have focused on controlling the enchainment of ether and carbonate segments, a process that determines the performance of the material. Here we report precise control of the enchainment of ether and carbonate segments by using a series of well-defined dinuclear organoboron catalysts. By altering the catalyst structure and optimizing reaction conditions, the alternating carbonate content in the propylene oxide/CO2 copolymer is finely regulated over a wide range of 3.0–95.2%, and the polyether content is arbitrarily varied between <0.1% and 97.0%. A unique microstructure, the -ABB- linkage, is identified by NMR spectroscopy, hydrolysis-derivatization experiments and single-crystal X-ray diffraction. Density functional theory calculations indicate that the -ABB- microstructure originates from a regioselectivity-directed copolymerization process. By analysis of the crystal structures of four catalysts and their catalytic performance, we quantified a correlation between dinuclear organoboron catalyst structure and sequence selectivity (-AB-, -ABB- and -ABn-, n ≥ 3) in propylene oxide/CO2 copolymerization, which should enable new catalyst design for this sustainable transformation.

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Fig. 1: Copolymerization of PO and CO2 mediated by organoboron catalysts.
Fig. 2: NMR spectroscopic characterization of the PO/CO2 copolymer (PO/7 = 1,000/1, mole ratio, 40 °C, 20 bar CO2 pressure).
Fig. 3: Determination of the microstructure of PO/CO2 copolymer.
Fig. 4: Optimization of the dinuclear organoboron catalysts for the copolymerization of PO and CO2.
Fig. 5: The proposed mechanism for PO/CO2 copolymerization using catalyst 7.
Fig. 6: The energy profile calculated using DFT for PO/CO2 copolymerization catalysed by the dinuclear organoboron catalyst.

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Data availability

Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition numbers CCDC 2012655 (7), 2123603 (8), 1974836 (9), 2091870 (D1) and 2091869 (D2). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures. All other data supporting the findings of this study are available within the Article and its Supplementary Information.

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Acknowledgements

Financial support from the Zhejiang Provincial Natural Science Foundation of China (LR21B040001 to G.-P.W.) and the National Natural Science Foundation of China (grants 91956123 to G.-P.W., 51973186 to G.-P.W., and 22101253 to G.-W.Y.) is gratefully acknowledged. Special thanks to W.-M. Ren in Dalian University of Technology for assistance with the GC–MS analysis.

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Authors and Affiliations

  1. MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China

    Guan-Wen Yang, Cheng-Kai Xu, Rui Xie, Yao-Yao Zhang, Chenjie Lu, Huan Qi, Li Yang, Yuhui Wang & Guang-Peng Wu

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Contributions

G.-W.Y. and G.-P.W. conceived the idea of the project. G.-W.Y. synthesized the catalysts. G.-W.Y, C.-K.X., Y.-Y.Z., C.L., H.Q., L.Y. and Y.W. performed the polymerizations. Y.-Y.Z. carried out the single-crystal X-ray diffraction study. R.X. performed the DFT calculations. G.-W.Y. and G.-P.W. analysed the data and wrote the manuscript. G.-P.W. directed the investigations.

Corresponding author

Correspondence to Guang-Peng Wu.

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Nature Synthesis thanks James Eagan and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary handling editor: Alison Stoddart, in collaboration with the Nature Synthesis team.

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Extended data

Extended Data Fig. 1 Effects of reaction temperature and CO2 pressure on sequence selectivity.

a, Sequence-control copolymerization of propylene oxide and CO2 with -AB-, -ABB-, and -ABn- (n ≥ 3) sequences using catalyst 7. b, The influence of reaction temperature and CO2 pressure on sequence selectivity. As shown, the selectivity of -AB-, -ABB-, and -ABn- (n ≥ 3) sequences is regulated over a wide range by varying the reaction conditions.

Source data

Supplementary information

Supplementary Information

Supplementary Figs. 1–18, procedures, DFT calculations, characterization, discussion and Tables 1–5.

Supplementary Data 1

Crystallographic data of catalyst_7 CCDC 2012655.

Supplementary Data 2

Crystallographic data of catalyst_8 CCDC 2123603.

Supplementary Data 3

Crystallographic data of catalyst_9 CCDC 1974836.

Supplementary Data 4

Crystallographic data of compound_D1 CCDC 2091870.

Supplementary Data 5

Crystallographic data of compound_D2 CCDC 2091869.

Source data

Source Data Fig. 4

Statistical source data.

Source Data Extended Data Fig. 1

Statistical source data.

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Yang, GW., Xu, CK., Xie, R. et al. Precision copolymerization of CO2 and epoxides enabled by organoboron catalysts. Nat. Synth 1, 892–901 (2022). https://doi.org/10.1038/s44160-022-00137-x

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