Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Closed-loop recycling of plastics enabled by dynamic covalent diketoenamine bonds

Nature Chemistry volume 11, pages 442–448 (2019)Cite this article

Subjects

Abstract

Recycled plastics are low-value commodities due to residual impurities and the degradation of polymer properties with each cycle of re-use. Plastics that undergo reversible polymerization allow high-value monomers to be recovered and re-manufactured into pristine materials, which should incentivize recycling in closed-loop life cycles. However, monomer recovery is often costly, incompatible with complex mixtures and energy-intensive. Here, we show that next-generation plastics—polymerized using dynamic covalent diketoenamine bonds—allow the recovery of monomers from common additives, even in mixed waste streams. Poly(diketoenamine)s ‘click’ together from a wide variety of triketones and aromatic or aliphatic amines, yielding only water as a by-product. Recovered monomers can be re-manufactured into the same polymer formulation, without loss of performance, as well as other polymer formulations with differentiated properties. The ease with which poly(diketoenamine)s can be manufactured, used, recycled and re-used—without losing value—points to new directions in designing sustainable polymers with minimal environmental impact.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Learn more

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Reversible, dynamic covalent diketoenamine bonds.
Fig. 2: Closed-loop recycling from dynamic covalent PDKs.
Fig. 3: Synthesis of network poly(ketoenamine)s by ball-milling.
Fig. 4: Mixed polymer decolouration, additive removal and closed-loop recycling of fibre-reinforced composites.
Fig. 5: Re-formulation of PDK networks.
Fig. 6: Dynamic covalent behaviour of PDK networks.

Data availability

The authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information, and also from the authors upon request. Crystallographic data for compounds 3, 5 and TK-6 are available free of charge from the Cambridge Crystallographic Date Centre (www.ccdc.cam.ac.uk) under reference nos. 1891131, 1891132 and 189113, respectively.

References

  1. Helms, B. A. & Russell, T. P. Polymer chemistries enabling cradle-to-cradle life cycles for plastics. Chem. 1, 813–819 (2016).

    Article  Google Scholar 

  2. Rahimi, A. R. & García, J. M. Chemical recycling of waste plastics for new materials production. Nat. Rev. Chem. 1, 0046 (2017).

    Article  Google Scholar 

  3. García, J. M. & Robertson, M. L. The future of plastics recycling. Science 358, 870–872 (2017).

    Article  Google Scholar 

  4. Hong, M. & Chen, E. Y.-X. Chemically recyclable polymers: a circular economy approach to sustainability. Green Chem. 19, 3692–3706 (2017).

    Article  CAS  Google Scholar 

  5. MacArthur, E. Beyond plastic waste. Science 358, 843 (2017).

    Article  CAS  Google Scholar 

  6. Schneiderman, D. K. & Hillmyer, M. A. 50th anniversary perspective: There is a great future in sustainable polymers. Macromolecules 50, 3733–3749 (2017).

    Article  CAS  Google Scholar 

  7. Sardon, H. & Dove, A. P. Plastics recycling with a difference. Science 360, 380–381 (2018).

    Article  CAS  Google Scholar 

  8. Geyer, R., Jambeck, J. R. & Law, K. L. Production, use, and fate of all plastics ever made. Sci. Adv. 3, e1700782 (2017).

    Article  Google Scholar 

  9. Zhang, X., Fevre, M., Jones, G. O. & Waymouth, R. M. Catalysis as an enabling science for sustainable polymers. Chem. Rev. 118, 839–885 (2018).

    Article  CAS  Google Scholar 

  10. Rowan, S. J., Cantrill, S. J., Cousins, G. R. L., Sanders, J. K. M. & Stoddart, J. F. Dynamic covalent chemistry. Angew. Chem. Int. Ed. 41, 898–952 (2002).

    Article  Google Scholar 

  11. Paszun, D. & Spychaj, T. Chemical recycling of poly(ethylene terephthalate). Ind. Eng. Chem. Res. 36, 1373–1383 (1997).

    Article  CAS  Google Scholar 

  12. Yoshioka, T., Motoki, T. & Okuwaki, A. Kinetics of hydrolysis of poly(ethylene terephthalate) powder in sulfuric acid by a modified shrinking-core model. Ind. Chem. Res. 40, 75–79 (2001).

    Article  CAS  Google Scholar 

  13. Kamber, N. E. et al. The depolymerization of poly(ethylene terephthalate) (PET) using N-heterocyclic carbenes from ionic liquids. J. Chem. Educ. 87, 519–521 (2010).

    Article  CAS  Google Scholar 

  14. Fukushima, K. et al. Organocatalytic depolymerization of poly(ethylene terephthalate). J. Polym. Sci. A 49, 1273–1281 (2011).

    Article  CAS  Google Scholar 

  15. Fukushima, K. et al. Advanced chemical recycling of poly(ethylene terephthalate) through organocatalytic aminolysis. Polym. Chem. 4, 1610–1616 (2013).

    Article  CAS  Google Scholar 

  16. Ying, H., Zhang, Y. & Cheng, J. Dynamic urea bond for the design of reversible and self-healing polymers. Nat. Commun. 5, 3218 (2014).

    Article  Google Scholar 

  17. Zhang, Y. et al. Malleable and recyclable poly(urea-urethane) thermosets bearing hindered urea bonds. Adv. Mater. 28, 7646–7651 (2016).

    Article  CAS  Google Scholar 

  18. Jia, X., Qin, C., Friedberger, T., Guan, Z. & Huang, Z. Efficient and selective degradation of polyethylenes into liquid fuels and waxes under mild conditions. Sci. Adv. 2, e1501591 (2016).

    Article  Google Scholar 

  19. Jones, G. O., Yuen, A., Wojtecki, R. J., Hedrick, J. L. & García, J. M. Computational and experimental investigations of one-step conversion of poly(carbonate)s into value-added poly(aryl ether sulfone)s. Proc. Natl Acad. Sci. USA 113, 7722–7726 (2016).

    Article  CAS  Google Scholar 

  20. García, J. M. et al. Recyclable, strong thermosets and organogels via paraformaldehyde condensation with diamines. Science 344, 732–735 (2014).

    Article  Google Scholar 

  21. Schneiderman, D. K. et al. Chemically recyclable biobased polyurethanes. ACS Macro. Lett. 5, 515–518 (2016).

    Article  CAS  Google Scholar 

  22. MacDonald, J. P. & Shaver, M. P. An aromatic/aliphatic polyester prepared via ring-opening polymerization and its remarkable selective and cyclable depolymerization to monomer. Polym. Chem. 7, 553–559 (2016).

    Article  CAS  Google Scholar 

  23. Tang, X. et al. The quest for converting biorenewable bifunctional α-methylene-γ-butyrolactone into degradable and recyclable polyester: controlling vinyl-addition/ring-opening/cross-linking pathways. J. Am. Chem. Soc. 138, 14326–14337 (2016).

    Article  CAS  Google Scholar 

  24. Hong, M. & Chen, E. Y.-X. Towards truly sustainable polymers: a metal-free recyclable polyester from biorenewable non-strained γ-butyrolactone. Angew. Chem. Int. Ed. 55, 4188–4193 (2016).

    Article  CAS  Google Scholar 

  25. Hong, M. & Chen, E. Y.-X. Completely recyclable biopolymers with linear and cyclic topologies via ring-opening polymerization of γ-butyrolactone. Nat. Chem. 8, 42–49 (2016).

    Article  CAS  Google Scholar 

  26. Zhu, J.-B., Watson, E. M., Tang, J. & Chen, E. Y.-X. A synthetic polymer system with repeatable chemical recyclability. Science 360, 398–403 (2018).

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  28. Denissen, W. et al. Vinylogous urethane vitrimers. Adv. Funct. Mater. 25, 2451–2457 (2015).

    Article  CAS  Google Scholar 

  29. 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 

  30. Obadia, M. M., Mudraboyina, B. P., Serghei, A., Montarnal, D. & Drockenmuller, E. Reprocessing and recycling of highly cross-linked ion-conduction networks through trans-alkylation exchanges of C–N bonds. J. Am. Chem. Soc. 137, 6078–6083 (2015).

    Article  CAS  Google Scholar 

  31. Taynton, P. et al. Repairable woven carbon-fiber composites with full recyclability enabled by malleable polyimine networks. Adv. Mater. 28, 2904–2909 (2016).

    Article  CAS  Google Scholar 

  32. Yu, K., Shi, Q., Dunn, M. L., Wang, T. & Qi, H. J. Carbon fiber reinforced thermoset composite with near 100% recyclability. Adv. Funct. Mater. 26, 6098–6106 (2016).

    Article  CAS  Google Scholar 

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

    Article  Google Scholar 

  34. Snyder, R. L., Fortman, D. J., De Hoe, G. X., Hillmyer, M. A. & Dichtel, W. R. Reprocessable acid-degradable polycarbonate vitrimers. Macromolecules 51, 389–397 (2018).

    Article  CAS  Google Scholar 

  35. Zou, Z. et al. Rehealable, fully recyclable, and malleable electronic skin enabled by dynamic covalent thermoset nanocomposite. Sci. Adv. 4, eaaq0508 (2018).

    Article  Google Scholar 

  36. Kolb, H. C., Finn, M. G. & Sharpless, K. B. Click chemistry: diverse chemical function from a few good reactions. Angew. Chem. Int. Ed. 40, 2004–2021 (2001).

    Article  CAS  Google Scholar 

  37. Kohout, M., Bielec, B., Steindl, P., Trettenhahn, G. & Lindner, W. Mechanistic aspects of the direct C-acylation of cyclic 1,3-diones with various unactivated carboxylic acids. Tetrahedron 71, 2698–2707 (2015).

    Article  CAS  Google Scholar 

  38. Augustyns, K., Kraas, W. & Jung, G. Investigation on the stability of the Dde protecting group used in peptide synthesis: migration to an unprotected lysine. J. Peptide Res. 51, 127–133 (1998).

    Article  CAS  Google Scholar 

  39. Chong, J. H., Sauer, M., Patrick, B. O. & MacLachlan, M. J. Highly stable keto-enamine salicylideneanilines. Org. Lett. 5, 3823–3826 (2003).

    Article  Google Scholar 

  40. Kandambeth, S. et al. Construction of crystalline 2D covalent organic frameworks with remarkable chemical (acid/base) stability via a combined reversible and irreversible route. J. Am. Chem. Soc. 134, 19524–19527 (2012).

    Article  CAS  Google Scholar 

  41. DeBlase, C. R., Silberstein, K. E., Truong, T.-T., Abruña, H. D. & Dichtel, W. R. β-Ketoenamine-linked covalent organic frameworks capable of pseudocapacitive energy storage. J. Am. Chem. Soc. 135, 16821–16824 (2013).

    Article  CAS  Google Scholar 

  42. Taylor, M. $180bn investment in plastic factories feeds global packaging binge. The Guardian (26 December 2017); https://www.theguardian.com/environment/2017/dec/26/180bn-investment-in-plastic-factories-feeds-global-packaging-binge

Download references

Acknowledgements

The technical scope of this work was supported by the Laboratory Directed Research and Development Program of Lawrence Berkeley National Laboratory under US Department of Energy contract no. DE-AC02–05CH11231. K.E.L. was supported by the US Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internship (SULI) programme. Portions of this work, including organic and polymer synthesis and characterization, were carried out as a User Project at the Molecular Foundry, which is supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231.

Author information

Authors and Affiliations

  1. The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Peter R. Christensen, Angelique M. Scheuermann, Kathryn E. Loeffler & Brett A. Helms

  2. Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA

    Angelique M. Scheuermann

  3. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Brett A. Helms

Authors
  1. Peter R. Christensen
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Angelique M. Scheuermann
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Kathryn E. Loeffler
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Brett A. Helms
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

B.A.H. and P.R.C. designed and planned the project. P.R.C. synthesized and characterized all PDK materials and their recyclability. A.M.S. synthesized small molecules and carried out experiments to measure the activation energies for amine exchange. K.E.L. carried out experiments to characterize the extent of network formation by ball-milling. B.A.H. and P.R.C. wrote the manuscript, with contributions from all co-authors.

Corresponding author

Correspondence to Brett A. Helms.

Ethics declarations

Competing interests

B.A.H. and P.R.C. are inventors on US provisional patent application 62/587,148 submitted by Lawrence Berkeley National Laboratory that covers poly(diketoenamine)s, as well as aspects of their use and recovery.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary information

Supplementary synthetic procedures, materials characterization, closed-loop polymer recycling, bond exchange kinetics, and Supplementary Figures 1–17.

Crystallographic data

CIF for compound 3; CCDC reference: 1891131.

Crystallographic data

CIF for compound 5; CCDC reference: 1891132.

Crystallographic data

CIF for compound TK-6; CCDC reference: 1891133.

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Christensen, P.R., Scheuermann, A.M., Loeffler, K.E. et al. Closed-loop recycling of plastics enabled by dynamic covalent diketoenamine bonds. Nat. Chem. 11, 442–448 (2019). https://doi.org/10.1038/s41557-019-0249-2

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41557-019-0249-2

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing