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The development of vitrimers with dynamic covalent bonds enables reprocessability in crosslinked networks, offering a sustainable alternative to conventional thermosets. In this work, a thiol-acrylate vitrimer was synthesized from lignin-derivable (bis)phenols (guaiacol and bisguaiacol F) and compared to a control derived from petroleum-based precursors (phenol and bisphenol F) to investigate the effect of structural differences on network properties and thermal reprocessing. The presence of methoxy groups in the lignin-derivable vitrimer promoted intermolecular interactions by serving as additional hydrogen bonding acceptors during curing, leading to a denser network, as evidenced by a higher rubbery storage modulus (∼2.4 MPa vs. ∼1.4 MPa) and glass transition temperature (∼34 °C vs. ∼28 °C). The lignin-derivable vitrimer exhibited a slightly higher elongation-at-break (∼170% vs. ∼130%) and improved mechanical robustness, including a nearly two-fold increase in Young's modulus (∼6.9 MPa vs. ∼3.4 MPa) and toughness (∼750 kJ m−3vs. ∼390 kJ m−3). The similar stress relaxation behavior and activation energy of viscous flow indicated comparable bond exchange dynamics between the two vitrimers, while the lignin-derivable system demonstrated higher thermal healing efficiency with improved recovery of tensile properties after reprocessing. These findings highlight the potential of lignin-based aromatics in designing mechanically robust and sustainable vitrimers, aligning with efforts to develop renewable and reprocessable polymeric materials.
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Structural effects on the reprocessability and stress relaxation of crosslinked polyhydroxyurethanes
ABSTRACT Crosslinked polyhydroxyurethane (PHU) networks synthesized from difunctional six‐membered cyclic carbonates and triamines are reprocessable at elevated temperatures through transcarbamoylation reactions. Here we study the structural effects on reprocessability and stress relaxation in crosslinked PHUs. Crosslinked PHUs derived frombis(five‐membered cyclic carbonates) are shown to decompose at temperatures needed for reprocessing, likely via initial reversion of the PHU linkage and subsequent side reactions of the liberated amine and cyclic carbonate. Therefore, several six‐membered cyclic carbonate‐based PHUs with varying polymer backbones and crosslink densities were synthesized. These networks show large differences in the Arrhenius activation energy of stress relaxation (from 99 to 136 kJ/mol) that depend on the network structure, suggesting that transcarbamoylation reactions may be highly affected by both chemical and mechanical effects. Furthermore, all crosslinked PHUs derived from six‐membered cyclic carbonates show mechanical properties typical of thermoset polymers, but recovered as much as 80% of their as‐synthesized tensile properties after elevated temperature compression molding. These studies provide significant insight into factors affecting the reprocessability of PHUs and inform design criteria for the future synthesis of sustainable and repairable crosslinked PHUs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2017,134, 44984.
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- Award ID(s):
- 1413862
- PAR ID:
- 10034597
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Applied Polymer Science
- Volume:
- 134
- Issue:
- 45
- ISSN:
- 0021-8995
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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