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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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.
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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.
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.
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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.
Optimized coordinates for the divinyloligocyclobutane dimer, trimer and butadiene using the B3LYP-D3 functional.
Optimized coordinates for the iron catalyst stationary points on the singlet energy surface using the B3LYP-D3 functional.
Optimized coordinates for the divinyloligocyclobutane dimer, trimer and butadiene using the M06L functional.
Optimized coordinates for the iron catalyst stationary points on the singlet energy surface using the M06L functional.
Optimized coordinates for the divinyloligocyclobutane dimer, trimer, and butadiene using the TPSSh functional.
Optimized coordinates for the iron catalyst stationary points using the broken symmetry (1,1) restrictions at the TPSSh level of theory.
Optimized coordinates for the iron catalyst stationary points using the broken symmetry (3,1) restrictions at the TPSSh level of theory.
Optimized coordinates for the iron catalyst stationary points on the singlet energy surface using the TPSSh functional.
Optimized coordinates for the iron catalyst stationary points on the triplet energy surface using the TPSSh functional.
Optimized coordinates for the iron catalyst stationary points on the quintet energy surface using the TPSSh functional.
Associated mae files for the calculated NMR shifts.
The resultant coordinates of the optimized geometries of the single strand oligomer.
The resultant coordinates of the optimized geometries of the supercell of the oligomer strands.
The raw data for the resultant coordinates of the optimized geometries of the single strand oligomer and supercell of the strands.
Combined spreadsheet comparing all functionals for all points in reaction profile.
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