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 from
- NSF-PAR ID:
- 10142427
- Date Published:
- Journal Name:
- Polymer Chemistry
- ISSN:
- 1759-9954
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Structural effects on the reprocessability and stress relaxation of crosslinked polyhydroxyurethanesmore » « less
ABSTRACT bis (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. -
null (Ed.)Recycling of polyurethanes is largely infeasible due to the harsh reprocessing conditions and associated risks of side reactions and degradation whereas polymer networks incorporating dynamic covalent bonds represent an attractive approach to the design of recyclable materials. Here, we report findings on the dynamic nature of thiourethanes, and their application as a new class of recyclable analogs of urethane materials. A series of small molecule experiments was initially conducted to determine the equilibrium constant and exchange reaction kinetic constant for the thiol–isocyanate reaction. Furthermore, incorporating those thiourethane moieties into a cross-linked network resulted in thermoset materials that are readily depolymerized to liquid oligomers. The resultant oligomers can be re-crosslinked to thiourethanes without any loss of performance nor change in mechanical properties (peak stress of 25 MPa with max strain of 200%). Moreover, the recycled thiol oligomers from thiourethane network polymers could potentially be transformed into other materials with mechanical properties that exceed those of the initial, pristine thiourethane materials. Overall, the ease with which these polythiourethanes are polymerized, recycled and reformulated gives a new direction and hope in the design of sustainable polymers.more » « less
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Abstract In order to better understand the design rules of epoxy–phenol thermosets we will report on the chemistry and (thermo)mechanical properties of cured epoxy–phenol thermoset films.
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Abstract The remarkable elasticity and tensile strength found in natural elastomers are challenging to mimic. Synthetic elastomers typically feature covalently cross‐linked networks (rubbers), but this hinders their reprocessability. Physical cross‐linking via hydrogen bonding or ordered crystallite domains can afford reprocessable elastomers, but often at the cost of performance. Herein, we report the synthesis of ultra‐tough, reprocessable elastomers based on linear alternating polymers. The incorporation of a rigid isohexide adjacent to urethane moieties affords elastomers with exceptional strain hardening, strain rate dependent behavior, and high optical clarity. Distinct differences were observed between isomannide and isosorbide‐based elastomers where the latter displays superior tensile strength and strain recovery. These phenomena are attributed to the regiochemical irregularities in the polymers arising from their distinct stereochemistry and respective inter‐chain hydrogen bonding.
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Abstract The remarkable elasticity and tensile strength found in natural elastomers are challenging to mimic. Synthetic elastomers typically feature covalently cross‐linked networks (rubbers), but this hinders their reprocessability. Physical cross‐linking via hydrogen bonding or ordered crystallite domains can afford reprocessable elastomers, but often at the cost of performance. Herein, we report the synthesis of ultra‐tough, reprocessable elastomers based on linear alternating polymers. The incorporation of a rigid isohexide adjacent to urethane moieties affords elastomers with exceptional strain hardening, strain rate dependent behavior, and high optical clarity. Distinct differences were observed between isomannide and isosorbide‐based elastomers where the latter displays superior tensile strength and strain recovery. These phenomena are attributed to the regiochemical irregularities in the polymers arising from their distinct stereochemistry and respective inter‐chain hydrogen bonding.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9PY01957J
