Cited by 424Polymer composites and self-healingMaterial Dynamics and PropertiesEpoxy Resin Curing Processes

Vitrimers Designed Both To Strongly Suppress Creep and To Recover Original Cross-Link Density after Reprocessing: Quantitative Theory and Experiments

Li, Lingqiao, Chen, Xi, Jin, Kailong, Torkelson, John M.·2018·Macromolecules

Abstract

Vitrimers form a promising class of dynamic polymer networks, but they have an Achilles’ heel: elastomeric vitrimers exhibit significant creep under conditions where permanently cross-linked, elastomeric networks exhibit little or no creep. We demonstrate that vitrimers can be designed with strongly suppressed creep and excellent reprocessability by incorporating a substantial yet subcritical fraction of permanent cross-links. This critical fraction of permanent cross-links, which has little or no detrimental effect on reprocessability, is defined by the gelation point of only permanent cross-links leading to a percolated permanent network. Via a modification of classic Flory–Stockmayer theory, we have developed a simple theory that quantitatively predicts an approximate limiting fraction. To test our theory, we designed vitrimers with controlled fractions of permanent cross-links based on thiol–epoxy click chemistry. We characterized the rubbery plateau modulus before and after reprocessing as well as stress relaxation of our original vitrimers. Our experimental results strongly support our theoretical prediction: as long as the fraction of permanent cross-links is insufficient to form a percolated permanent network, the vitrimer can be reprocessed with full recovery of cross-link density. In particular, with a predicted limiting fraction of 50 mol %, a vitrimer system designed with 40 mol % permanent cross-links achieved full property recovery associated with cross-link density after reprocessing as well as 65–71% creep reduction (for both original and reprocessed samples) relative to a similar vitrimer without permanent cross-links. In contrast, a system with 60 mol % permanent cross-links could not be reprocessed into a well-consolidated sample, nor did it recover full cross-link density; it failed by breaking at early stages of creep tests. The ability to predict an approximate limiting fraction of permanent cross-links leading to enhanced creep resistance and full reprocessability represents an important advance in the science and design of vitrimers.

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Crossref · 10.1021/acs.macromol.8b00922

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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”

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Authors
Li, L., Chen, X., Jin, K., & Torkelson, J. M.
Affiliations
Northwestern University (US)
Corresponding author
Torkelson, John M.
Venue
Macromolecules
Published
2018-07-17
Volume
51
Issue
15
Pages
5537-5546
ISSN
  • 0024-9297 (ISSN-L)
  • 1520-5835
OpenAlex
W2884182729
Cited by
424
References
64
Citations by year
2026: 55 · 2025: 89 · 2024: 69 · 2023: 65 · 2022: 57 · 2021: 38 · 2020: 30 · 2019: 20 · 2018: 1
FWCI
11.10
Type
journal article
Language
en
Open access
closed
Locations
Macromolecules (publishedVersion)
Funders
Northwestern University
Topics
  • Physical Sciences › Materials Science › Polymers and Plastics › Polymer composites and self-healing
  • Physical Sciences › Materials Science › Materials Chemistry › Material Dynamics and Properties
  • Physical Sciences › Engineering › Mechanical Engineering › Epoxy Resin Curing Processes
Keywords
vitrimers, reprocessability, dynamic polymer networks, percolation network, Flory-Stockmayer theory, stress relaxation, rubbery plateau modulus, gel point

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