Iron-catalysed synthesis and chemical recycling of telechelic 1,3-enchained oligocyclobutanes

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Abstract

Closed-loop recycling offers the opportunity to mitigate plastic waste through reversible polymer construction and deconstruction. Although examples of chemical recycling of polymers are known, few have been applied to materials derived from abundant commodity olefinic monomers, which are the building blocks of ubiquitous plastic resins. Here we describe a [2+2] cycloaddition/oligomerization of 1,3-butadiene to yield a previously unrealized telechelic microstructure of (1,n′-divinyl)oligocyclobutane. This material is thermally stable, has stereoregular segments arising from chain-end control, and exhibits high crystallinity even at low molecular weight. Exposure of the oligocyclobutane to vacuum in the presence of the pyridine(diimine) iron precatalyst used to synthesize it resulted in deoligomerization to generate pristine butadiene, demonstrating a rare example of closed-loop chemical recycling of an oligomeric material derived from a commodity hydrocarbon feedstock.

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Fig. 1: Approaches to closed-loop recycling of polymers.
Fig. 2: A unique microstructure of polybutadiene obtained through iron-catalysed [2+2]-cycloaddition/oligomerization.
Fig. 3: Select thermal data for crystalline (1,n′-divinyl)polycyclobutane.
Fig. 4: Molecular dynamics simulated (1,17′-divinyl)polycyclobutane oligomer.
Fig. 5: Proposed catalytic cycle for the generation of oligocyclobutanes.
Fig. 6: Catalytic chemical recycling of cyclobutane structures.

Data availability

All data necessary to support the conclusions of this paper are provided in the Supplementary Information, including optimized DFT coordinates and energetics, calculated free energies and MD equilibrated coordinates.

Change history

  • 22 February 2021

    In the version of this Article originally published, the Supplementary Information PDF was missing. This has now been corrected.

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Acknowledgements

We are grateful to S. Klemenz and the Schoop laboratory for initial assistance with powder diffraction, as well as D. Gregory for assistance with TGA/GCMS and DSC. M.M.B. thanks K. Conover for assistance with high-temperature NMR experiments. M.M.B., C.R.K. and P.J.C. thank Firmenich for initial support of this work. M.M.B. and C.R.K. thank the NIH for Ruth L. Kirschstein National Research Service Awards (F32 GM134610 and GM126640). All authors thank ExxonMobil for support of this research.

Author information

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Authors

Contributions

C.R.K. and P.J.C. conceived the project. C.R.K. and M.M.B. performed experiments regarding the synthesis and partial characterization of oligomers. A.E.C. and S.J.M. conducted full NMR characterization and peak assignments. M.M.B., A.E.C. and J.A.T. performed experiments on the thermal stability and crystallinity of the oligomer. J.M.Y. conducted TST/DFT and molecular mechanics calculations. M.M.B. and A.E.C. performed the chemical recycling experiments.

Corresponding author

Correspondence to Paul J. Chirik.

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Competing interests

C.R.K. and P.J.C. are inventors on patent application US 2019/0211142 A1 titled ‘Oligomeric and polymeric species comprising cyclobutane units’. J.M.Y., A.E.C., S.J.M. and J.A.T. are employees of ExxonMobil Chemical Company.

Additional information

Peer review information Nature Chemistry thanks the anonymous reviewers for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–22, Tables 1–9 and references 1–34. Spectroscopic data for the oligocyclobutanes, chemical/stereochemical NMR shift assignments, DFT NMR simulations, WAXS data and MD simulations, TGA and DSC data, spectroscopic data for chemical recycling, gelation tests and DFT simulations of the reaction profile and associated discussion.

Supplementary Data 1

Optimized coordinates for the divinyloligocyclobutane dimer, trimer and butadiene using the B3LYP-D3 functional.

Supplementary Data 2

Optimized coordinates for the iron catalyst stationary points on the singlet energy surface using the B3LYP-D3 functional.

Supplementary Data 3

Optimized coordinates for the divinyloligocyclobutane dimer, trimer and butadiene using the M06L functional.

Supplementary Data 4

Optimized coordinates for the iron catalyst stationary points on the singlet energy surface using the M06L functional.

Supplementary Data 5

Optimized coordinates for the divinyloligocyclobutane dimer, trimer, and butadiene using the TPSSh functional.

Supplementary Data 6

Optimized coordinates for the iron catalyst stationary points using the broken symmetry (1,1) restrictions at the TPSSh level of theory.

Supplementary Data 7

Optimized coordinates for the iron catalyst stationary points using the broken symmetry (3,1) restrictions at the TPSSh level of theory.

Supplementary Data 8

Optimized coordinates for the iron catalyst stationary points on the singlet energy surface using the TPSSh functional.

Supplementary Data 9

Optimized coordinates for the iron catalyst stationary points on the triplet energy surface using the TPSSh functional.

Supplementary Data 10

Optimized coordinates for the iron catalyst stationary points on the quintet energy surface using the TPSSh functional.

Supplementary Data 11

Associated mae files for the calculated NMR shifts.

Supplementary Data 12

The resultant coordinates of the optimized geometries of the single strand oligomer.

Supplementary Data 13

The resultant coordinates of the optimized geometries of the supercell of the oligomer strands.

Supplementary Data 14

The raw data for the resultant coordinates of the optimized geometries of the single strand oligomer and supercell of the strands.

Supplementary Data 15

Combined spreadsheet comparing all functionals for all points in reaction profile.

Supplementary Data 16

Combined spreadsheet comparing all spin manifolds for all points in reaction profile.

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Mohadjer Beromi, M., Kennedy, C.R., Younker, J.M. et al. Iron-catalysed synthesis and chemical recycling of telechelic 1,3-enchained oligocyclobutanes. Nat. Chem. 13, 156–162 (2021). https://doi.org/10.1038/s41557-020-00614-w

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