Reprocessable Polymer Networks via Thiourethane Dynamic Chemistry: Recovery of Cross-link Density after Recycling and Proof-of-Principle Solvolysis Leading to Monomer Recovery
Abstract
Polythiourethane (PTU) can be synthesized by a type of click chemistry involving the reaction of thiols with isocyanates. To our knowledge, thiourethane dynamic chemistry has not been significantly explored from a fundamental standpoint and has only begun to be studied regarding its use in producing recyclable, reprocessable substitutes for traditional cross-linked polyurethane networks. Using model compounds, we demonstrated the dual nature of the mechanism associated with catalyzed thiourethane dynamic chemistry: at elevated temperature, thiourethane groups undergo exchange reactions with free thiol groups and thermal reversion to thiols and isocyanates. We used this chemistry to synthesize cross-linked PTU elastomers which, upon optimization, achieve full recovery of cross-link density and tensile properties after multiple, relatively rapid remolding cycles. We characterized stress relaxation as a function of temperature and stoichiometric imbalance to provide insight into the mechanism of the network structure change. A small level (10 mol %) of excess thiol groups reduces reversion, thereby suppressing undesired side reactions during reprocessing and promoting thiol–thiourethane exchange reactions, leading to excellent property recovery after multiple recycling steps. With a proof-of-concept demonstration, we also revealed the potential of recovering thiol monomer by solvolysis from PTU networks, which provides a second route for sustainable recycling. In addition to introducing thiourethane dynamic chemistry as a simple way to achieve high-value recyclability of polyurethane-type networks by reprocessing and/or monomer recovery, our study shows that tuning of the reaction stoichiometry may be a facile approach to optimize property recovery after reprocessing for some dynamic networks that exhibit property loss when at stoichiometric balance.
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Existing strategies to create reprocessable thermosets have focused on dynamic covalent bond exchange, thermomechanical degradation, or wholesale replacement of network components with degradable versions.
“Existing strategies to create reprocessable thermosets have focused on dynamic covalent bond exchange, 3-8 thermomechanical degradation, 9 or wholesale replacement of network components with degradable versions. 10-13”
From Cleavable comonomers enable degradable, recyclable thermoset plastics (2020) · cites this paper as [12]
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Cleavable comonomers enable degradable, recyclable thermoset plastics
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- Authors
- Li, L., Chen, X., & Torkelson, J. M.
- Affiliations
- Northwestern University (US)
- Corresponding author
- Torkelson, John M.
- Venue
- Macromolecules
- Publisher
- American Chemical Society (ACS)
- Published
- 2019-10-22
- Volume
- 52
- Issue
- 21
- Pages
- 8207-8216
- ISSN
- 0024-9297 (ISSN-L)
- 1520-5835
- OpenAlex
- W2981485444
- Cited by
- 224
- References
- 60
- Citations by year
- 2026: 31 · 2025: 29 · 2024: 34 · 2023: 48 · 2022: 29 · 2021: 25 · 2020: 28
- FWCI
- 8.75
- Type
- journal article
- Language
- en
- Open access
- closed
- Licence
- Locations
- Macromolecules (publishedVersion)
- Funders
- Division of Chemistry (1048773)
- Division of Electrical, Communications and Cyber Systems (1542205)
- 3M
- Northwestern University
- International Institute for Nanotechnology
- State of Illinois
- Topics
- Physical Sciences › Materials Science › Polymers and Plastics › Polymer composites and self-healing
- Physical Sciences › Materials Science › Polymers and Plastics › Polymer crystallization and properties
- Physical Sciences › Chemistry › Organic Chemistry › Advanced Polymer Synthesis and Characterization
- Keywords
- polythiourethane, crosslinked elastomers, recycling, thermal reversion, stress relaxation, reaction stoichiometry, solvolysis, monomer recovery, sustainable recycling
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