Thermoreversible [2+2] Photodimers of Monothiomaleimides and Intrinsically Recyclable Covalent Networks Thereof. Aljuaid, M., Chang, Y., Haddleton, D. M., Wilson, P., & Houck, H. A. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 146(28):19177–19182, July, 2024.
doi  abstract   bibtex   
The development of intrinsically recyclable cross-linked materials remains challenged by the inherently unfavorable chemical equilibrium that dictates the efficiency of the reversible covalent bonding/debonding chemistry. Rather than having to (externally) manipulate the bonding equilibrium, we here introduce a new reversible chemistry platform based on monosubstituted thiomaleimides that can undergo complete and independent light-activated covalent bonding and on-demand thermal debonding above 120 degrees C. Specifically, repeated bonding/debonding of a small-molecule thiomaleimide [2 + 2] photodimer is demonstrated over five heat/light cycles with full conversion in both directions, thereby regenerating its initial monothiomaleimide constituents. This motivated the synthesis of multifunctional thiomaleimide reagents as precursors for the design of covalently cross-linked networks that display intrinsic switching between a monomeric and polymeric state. The resulting materials are shown to covalently dissociate and depolymerize upon heating both in solution and in bulk, thus transforming the densely photo-cross-linked material back into a viscous liquid. Temperature-regulated photorheology evidenced the intrinsic recyclability of the thiomaleimide-based thermosets during multiple cycles of UV cross-linking and thermal de-cross-linking. The thermally reversible photodimerization of thiomaleimides presents a new addition to the designer playground of dynamic polymer networks, providing interesting opportunities for the reprocessing and closed-loop recycling of covalently cross-linked materials.
@article{aljuaid_thermoreversible_2024,
	title = {Thermoreversible [2+2] {Photodimers} of {Monothiomaleimides} and {Intrinsically} {Recyclable} {Covalent} {Networks} {Thereof}},
	volume = {146},
	issn = {0002-7863},
	doi = {10.1021/jacs.4c04193},
	abstract = {The development of intrinsically recyclable cross-linked materials remains challenged by the inherently unfavorable chemical equilibrium that dictates the efficiency of the reversible covalent bonding/debonding chemistry. Rather than having to (externally) manipulate the bonding equilibrium, we here introduce a new reversible chemistry platform based on monosubstituted thiomaleimides that can undergo complete and independent light-activated covalent bonding and on-demand thermal debonding above 120 degrees C. Specifically, repeated bonding/debonding of a small-molecule thiomaleimide [2 + 2] photodimer is demonstrated over five heat/light cycles with full conversion in both directions, thereby regenerating its initial monothiomaleimide constituents. This motivated the synthesis of multifunctional thiomaleimide reagents as precursors for the design of covalently cross-linked networks that display intrinsic switching between a monomeric and polymeric state. The resulting materials are shown to covalently dissociate and depolymerize upon heating both in solution and in bulk, thus transforming the densely photo-cross-linked material back into a viscous liquid. Temperature-regulated photorheology evidenced the intrinsic recyclability of the thiomaleimide-based thermosets during multiple cycles of UV cross-linking and thermal de-cross-linking. The thermally reversible photodimerization of thiomaleimides presents a new addition to the designer playground of dynamic polymer networks, providing interesting opportunities for the reprocessing and closed-loop recycling of covalently cross-linked materials.},
	number = {28},
	urldate = {2024-07-10},
	journal = {JOURNAL OF THE AMERICAN CHEMICAL SOCIETY},
	author = {Aljuaid, Mohammed and Chang, Yujing and Haddleton, David M. and Wilson, Paul and Houck, Hannes A.},
	month = jul,
	year = {2024},
	pages = {19177--19182},
}

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