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Cleavable comonomers enable degradable, recyclable thermoset plastics

Nature volume 583, pages 542–547 (2020)Cite this article

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A Publisher Correction to this article was published on 20 August 2020

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Abstract

Thermosets—polymeric materials that adopt a permanent shape upon curing—have a key role in the modern plastics and rubber industries, comprising about 20 per cent of polymeric materials manufactured today, with a worldwide annual production of about 65 million tons1,2. The high density of crosslinks that gives thermosets their useful properties (for example, chemical and thermal resistance and tensile strength) comes at the expense of degradability and recyclability. Here, using the industrial thermoset polydicyclopentadiene as a model system, we show that when a small number of cleavable bonds are selectively installed within the strands of thermosets using a comonomer additive in otherwise traditional curing workflows, the resulting materials can display the same mechanical properties as the native material, but they can undergo triggered, mild degradation to yield soluble, recyclable products of controlled size and functionality. By contrast, installation of cleavable crosslinks, even at much higher loadings, does not produce degradable materials. These findings reveal that optimization of the cleavable bond location can be used as a design principle to achieve controlled thermoset degradation. Moreover, we introduce a class of recyclable thermosets poised for rapid deployment.

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Fig. 1: Conceptual basis of this work.
Fig. 2: Precise placement of a small number of degradable bonds within the strands of pDCPD thermosets enables degradation into soluble products.
Fig. 3: Functional evaluation of doped pDCPD.
Fig. 4: Soluble pDCPD fragments enable high-resolution characterization of pDCPD and can be recycled into new materials.

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All data supporting the findings of this study are available within this Article and its Supplementary Information and from the corresponding author upon reasonable request. Source data are provided with this paper.

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References

  1. Ma, S. & Webster, D. C. Degradable thermosets based on labile bonds or linkages: a review. Prog. Polym. Sci. 76, 65–110 (2018).

    Article  CAS  Google Scholar 

  2. Post, W., Susa, A., Blaauw, R., Molenveld, K. & Knoop, R. J. I. A review on the potential and limitations of recyclable thermosets for structural applications. Polym. Rev. 60, 359–388 (2020).

    Article  CAS  Google Scholar 

  3. Kloxin, C. J., Scott, T. F., Adzima, B. J. & Bowman, C. N. Covalent adaptable networks (CANs): a unique paradigm in cross-linked polymers. Macromolecules 43, 2643–2653 (2010).

    Article  ADS  CAS  Google Scholar 

  4. Gu, Y., Zhao, J. & Johnson, J. A. Polymer networks: from plastics and gels to porous frameworks. Angew. Chem. Int. Ed. 59, 5022–5049 (2020).

    Article  CAS  Google Scholar 

  5. Winne, J. M., Leibler, L. & Du Prez, F. E. Dynamic covalent chemistry in polymer networks: a mechanistic perspective. Polym. Chem. 10, 6091–6108 (2019).

    Article  CAS  Google Scholar 

  6. Montarnal, D., Capelot, M., Tournilhac, F. & Leibler, L. Silica-like malleable materials from permanent organic networks. Science 334, 965–968 (2011).

    Article  ADS  CAS  Google Scholar 

  7. Röttger, M. et al. High-performance vitrimers from commodity thermoplastics through dioxaborolane metathesis. Science 356, 62–65 (2017).

    Article  ADS  Google Scholar 

  8. Li, L., Chen, X., Jin, K. & Torkelson, J. M. Vitrimers designed both to strongly suppress creep and to recover original cross-link density after reprocessing: quantitative theory and experiments. Macromolecules 51, 5537–5546 (2018).

    Article  ADS  CAS  Google Scholar 

  9. Asaro, L., Gratton, M., Seghar, S. & Aït Hocine, N. Recycling of rubber wastes by devulcanization. Resour. Conserv. Recycling 133, 250–262 (2018).

    Article  Google Scholar 

  10. Yang, S. et al. Reworkable epoxies: thermosets with thermally cleavable groups for controlled network breakdown. Chem. Mater. 10, 1475–1482 (1998).

    Article  CAS  Google Scholar 

  11. Christensen, P. R., Scheuermann, A. M., Loeffler, K. E. & Helms, B. A. Closed-loop recycling of plastics enabled by dynamic covalent diketoenamine bonds. Nat. Chem. 11, 442–448 (2019).

    Article  CAS  Google Scholar 

  12. Li, L., Chen, X. & Torkelson, J. M. Reprocessable polymer networks via thiourethane dynamic chemistry: recovery of cross-link density after recycling and proof-of-principle solvolysis leading to monomer recovery. Macromolecules 52, 8207–8216 (2019).

    Article  ADS  CAS  Google Scholar 

  13. Fortman, D. J., Brutman, J. P., Cramer, C. J., Hillmyer, M. A. & Dichtel, W. R. Mechanically activated, catalyst-free polyhydroxyurethane vitrimers. J. Am. Chem. Soc. 137, 14019–14022 (2015).

    Article  CAS  Google Scholar 

  14. Rule, J. D. & Moore, J. S. ROMP reactivity of endo- and exo-dicyclopentadiene. Macromolecules 35, 7878–7882 (2002).

    Article  ADS  CAS  Google Scholar 

  15. Kessler, M. R. & White, S. R. Cure kinetics of the ring-opening metathesis polymerization of dicyclopentadiene. J. Polym. Sci. A 40, 2373–2383 (2002).

    Article  CAS  Google Scholar 

  16. Robertson, I. D. et al. Rapid energy-efficient manufacturing of polymers and composites via frontal polymerization. Nature 557, 223–227 (2018).

    Article  ADS  CAS  Google Scholar 

  17. Shieh, P., Nguyen, H. V. T. & Johnson, J. A. Tailored silyl ether monomers enable backbone-degradable polynorbornene-based linear, bottlebrush and star copolymers through ROMP. Nat. Chem. 11, 1124–1132 (2019).

    Article  CAS  Google Scholar 

  18. Wang, B., Ma, S., Yan, S. & Zhu, J. Readily recyclable carbon fiber reinforced composites based on degradable thermosets: a review. Green Chem. 21, 5781–5796 (2019).

    Article  CAS  Google Scholar 

  19. Fortman, D. J. et al. Approaches to sustainable and continually recyclable cross-linked polymers. ACS Sustain. Chem.& Eng. 6, 11145–11159 (2018).

    CAS  Google Scholar 

  20. Takahashi, A., Ohishi, T., Goseki, R. & Otsuka, H. Degradable epoxy resins prepared from diepoxide monomer with dynamic covalent disulfide linkage. Polymer 82, 319–326 (2016).

    Article  CAS  Google Scholar 

  21. Wiles, D. M. & Scott, G. Polyolefins with controlled environmental degradability. Polym. Degrad. Stabil. 91, 1581–1592 (2006).

    Article  CAS  Google Scholar 

  22. Sommazzi, A. & Garbassi, F. Olefin-carbon monoxide copolymers. Prog. Polym. Sci. 22, 1547–1605 (1997).

    Article  CAS  Google Scholar 

  23. Macosko, C. W. & Miller, D. R. A new derivation of average molecular weights of nonlinear polymers. Macromolecules 9, 199–206 (1976).

    Article  ADS  CAS  Google Scholar 

  24. Flory, P. J. Molecular size distribution in three dimensional polymers. I. Gelation. J. Am. Chem. Soc. 63, 3083–3090 (1941).

    Article  CAS  Google Scholar 

  25. Stockmayer, W. H. Theory of molecular size distribution and gel formation in branched polymers: II. General cross linking. J. Chem. Phys. 12, 125–131 (1944).

    Article  ADS  CAS  Google Scholar 

  26. Wang, J. et al. Counting loops in sidechain-crosslinked polymers from elastic solids to single-chain nanoparticles. Chem. Sci. 10, 5332–5337 (2019).

    Article  CAS  Google Scholar 

  27. Takayama, S. et al. Topographical micropatterning of poly(dimethylsiloxane) using laminar flows of liquids in capillaries. Adv. Mater. 13, 570–574 (2001).

    Article  CAS  Google Scholar 

  28. Long, T. R. et al. Ballistic response of polydicyclopentadiene vs. epoxy resins and effects of crosslinking. In Conference Proceedings of the Society for Experimental Mechanics Series 1B, 285–290 (Springer, 2017).

  29. Veysset, D. et al. Dynamics of supersonic microparticle impact on elastomers revealed by real-time multi-frame imaging. Sci. Rep. 6, 25577 (2016); corrigendum 8, 46944 (2018).

    Article  ADS  Google Scholar 

  30. Davies, J. S., Higginbotham, C. L., Tremeer, E. J., Brown, C. & Treadgold, R. C. Protection of hydroxy groups by silylation: use in peptide synthesis and as lipophilicity modifiers for peptides. J. Chem. Soc. Perkin Trans. I 3043, (1992).

  31. Tournier, V. et al. An engineered PET depolymerase to break down and recycle plastic bottles. Nature 580, 216–219 (2020).

    Article  ADS  CAS  Google Scholar 

  32. Cole, M., Lindeque, P., Halsband, C. & Galloway, T. S. Microplastics as contaminants in the marine environment: a review. Mar. Pollut. Bull. 62, 2588–2597 (2011).

    Article  CAS  Google Scholar 

  33. Hann, S., Ettlinger, S., Gibbs, A. & Hogg, D. The Impact of the Use of ‘Oxo-degradable’ Plastic on the Environment (Publications Office of the European Union, 2016); https://op.europa.eu/en/publication-detail/-/publication/bb3ec82e-9a9f-11e6-9bca-01aa75ed71a1.

  34. Autenrieth, B. et al. Stereospecific ring-opening metathesis polymerization (ROMP) of endo-dicyclopentadiene by molybdenum and tungsten catalysts. Macromolecules 48, 2480–2492 (2015).

    Article  ADS  CAS  Google Scholar 

  35. Chen, J., Burns, F. P., Moffitt, M. G. & Wulff, J. E. Thermally crosslinked functionalized polydicyclopentadiene with a high Tg and tunable surface energy. ACS Omega 1, 532–540 (2016).

    Article  CAS  Google Scholar 

  36. Albertsson, A. C. & Hakkarainen, M. Designed to degrade. Science 358, 872–873 (2017).

    Article  ADS  CAS  Google Scholar 

  37. Flory, P. J. Random reorganization of molecular weight distribution in linear condensation polymers. J. Am. Chem. Soc. 64, 2205–2212 (1942).

    Article  CAS  Google Scholar 

  38. Lee, J. H. et al. High strain rate deformation of layered nanocomposites. Nat. Commun. 3, 1164 (2012).

    Article  ADS  Google Scholar 

  39. Imbriglio, S. I. et al. Adhesion strength of titanium particles to alumina substrates: a combined cold spray and LIPIT study. Surf. Coat. Tech. 361, 403–412 (2019).

    Article  CAS  Google Scholar 

  40. Sun, Y. et al. Molecular dependencies of dynamic stiffening and strengthening through high strain rate microparticle impact of polyurethane and polyurea elastomers. Appl. Phys. Lett. 115, 093701 (2019).

    Article  ADS  Google Scholar 

  41. Veysset, D., Hsieh, A. J., Kooi, S. E. & Nelson, K. A. Molecular influence in high-strain-rate microparticle impact response of poly(urethane urea) elastomers. Polymer 123, 30–38 (2017).

    Article  CAS  Google Scholar 

  42. Parker, K. M. & Mitch, W. A. Halogen radicals contribute to photooxidation in coastal and estuarine waters. Proc. Natl Acad. Sci. USA 113, 5868–5873 (2016).

    Article  ADS  CAS  Google Scholar 

Download references

Acknowledgements

We thank the National Science Foundation (DMREF CHE-1629358) and the National Institutes of Health (1R01CA220468-01) for support of this work. P.S. was supported by a fellowship from the American Cancer Society. S.L.K. was supported by a fellowship from the Misrock Fund. We thank B. Adams and W. Massefski for assistance with NMR analysis, A. Schwartzman for assistance with AFM and nanoindentation measurements, T. McClure for assistance with ICP-OES measurements, M. Tarkanian for assistance with mould fabrication, and S.-X. Luo for assistance with Raman measurements. J.L., D.V., Y.S. and K.A.N. acknowledge support for the microparticle impact experiments from the US Army Research Office through the Institute for Soldier Nanotechnologies, under Cooperative Agreement number W911NF-18-2-0048.

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Authors and Affiliations

  1. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA

    Peyton Shieh, Wenxu Zhang, Keith E. L. Husted, Samantha L. Kristufek, David J. Lundberg, Jet Lem, David Veysset, Yuchen Sun, Keith A. Nelson & Jeremiah A. Johnson

  2. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA

    Boya Xiong & Desiree L. Plata

  3. Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA

    David J. Lundberg

  4. Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, MA, USA

    Jet Lem, Yuchen Sun & Keith A. Nelson

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  1. Peyton Shieh
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Contributions

P.S. and J.A.J. conceived of the idea. P.S., W.Z. and K.E.L.H. synthesized the materials. P.S., W.Z., S.L.K. and K.E.L.H. characterized the materials. D.J.L., P.S. and J.A.J. developed the theoretical framework. B.X. and D.L.P. conducted accelerated weathering experiments. D.J.L. performed techno-economic analyses. J.L., D.V., Y.S. and K.A.N. designed and conducted microparticle impact experiments. P.S. and J.A.J. wrote the manuscript. All authors read and revised the manuscript.

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Correspondence to Jeremiah A. Johnson.

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Competing interests

P.S., W.Z., K.E.L.H. and J.A.J. are named inventors on patent applications (US Patent Application 16/542,824 and US Provisional Application 62/935,799) filed by the Massachusetts Institute of Technology on the copolymers described in this work.

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Extended data figures and tables

Extended Data Fig. 1 The reverse gel-point concept used to derive the model of degradable thermosets shown in Fig. 1b.

a, A thermoset network containing f potential crosslinks per strand, c actual crosslinks per strand and x cleavable bonds within each strand may or may not be degraded into soluble fragments after bond cleavage. A model that determines whether the material will dissolve can be described as a function of f, c and x (Fig. 1b). b, The reverse gel-point concept enables this model by assuming that the minimum x required to enable thermoset degradation for given c and f values corresponds to the value that will inhibit the gelation of degradation fragments derived from strands with f potential crosslinking sites and x cleavable bonds. We use existing gelation theories (Miller–Macosko and Flory–Stockmayer) to solve for x, given f and c. Key to the reverse gel-point concept is the assumption that the network structure formed by the crosslinking of linear copolymer strands followed by cleavage of degradable bonds in those strands is identical to the network formed by first cleaving the linear copolymer strands and then crosslinking the resulting degradation products.

Extended Data Fig. 2 Characterization of pDCPD.

a, Images of pDCPD with various amounts of iPrSi and without iPrSi. b, Images of pDCPD with and without 20 vol% SiXL. c, pDCPD doped with up to 80 vol% SiXL remains intact after 12 h of TBAF treatment.

Extended Data Fig. 3 Further quantification of the impact of silyl ether incorporation into pDCPD strands.

a, Samples containing different amounts of iPrSi (0, 2.5, 5, 7.5 and 10 vol%) were incubated in 0.5 M TBAF in THF overnight, showing iPrSi-dependent degradation. b, Loss moduli for native pDCPD and 2.5% and 5% iPrSi-doped samples before and after TBAF treatment, as measured by oscillatory rheology. The storage moduli are presented in Fig. 2c. c, THF swelling ratios (THF swollen mass divided by dry mass) for native pDCPD and 2.5% and 5% iPrSi-doped samples following TBAF treatment. Centre values denote average. Error bars denote s.e.m. n = 3 for all samples.

Extended Data Fig. 4 Characterization of mechanical and thermal properties of iPrSi-doped pDCPD by DMA.

a, Loss factor (tan(delta)) plots of pDCPD samples as a function of iPrSi incorporation. b, Storage moduli collected at Tg – 60 °C for all samples. Centre values denote average. Error bars denote s.e.m. n = 3, except for the 33% sample, for which n = 5.

Extended Data Fig. 5 Synthesis and degradation of EtSi- and iPrSi-doped pDCPD.

a, Structure of EtSi, which differs from iPrSi in terms of the alkyl substituents on the silyl ether group. The less sterically hindered ethyl groups render this monomer more susceptible to cleavage. b, Images of 10% EtSi- or iPrSi-doped pDCPD. c, 10% EtSi dissolves in 0.5 M TBAF in THF after 12 h. d, Images of 10% EtSi-doped (left) and iPrSi-doped (right) pDCPD exposed to THF containing 15% concentrated aqueous HCl (12.1 N). The EtSi sample shows noticeably more rapid degradation under these conditions as compared to the iPrSi sample. Both samples are largely degraded within 12 h. In this case, acidic hydrolysis is facilitated by the presence of organic solvent to swell the network.

Extended Data Fig. 6 Weathering studies.

a, The weathering setup. Samples were kept inside glass vials over the course of the weathering experiments. b, Measured irradiance for samples during the weathering experiments and comparison to solar reference spectra (ASTM G177). c, Ultraviolet–visible spectra for the 0%, 10% and 20% iPrSi- and 10% EtSi-doped pDCPD samples. The sample thickness was 1 mm. d, Images of samples before and after the weathering studies.

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Shieh, P., Zhang, W., Husted, K.E.L. et al. Cleavable comonomers enable degradable, recyclable thermoset plastics. Nature 583, 542–547 (2020). https://doi.org/10.1038/s41586-020-2495-2

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