Mohammed Aljuaid, Yujing Chang, David M. Haddleton, Paul Wilson and Hannes A. Houck*,
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引用次数: 0
摘要
固有的不利化学平衡决定了可逆共价键合/脱键化学反应的效率,这对开发内在可回收交联材料提出了挑战。我们在此介绍一种基于单取代硫代马来酰亚胺的新型可逆化学平台,它无需(从外部)操纵键合平衡,就能在 120 °C 以上的温度下进行完全独立的光激活共价键合和按需热脱键。具体来说,小分子硫代马来酰亚胺[2 + 2]光二聚体在五个热/光循环中反复键合/脱键,实现了双向完全转化,从而再生出最初的单硫代马来酰亚胺成分。这促使人们合成了多功能硫代马来酰亚胺试剂,作为设计共价交联网络的前体,这种网络在单体和聚合物状态之间显示出内在的切换。结果表明,在溶液和块体中加热时,所产生的材料会共价解离和解聚,从而将密集光交联的材料变回粘性液体。温度调节光流变学证明了硫代马来酰亚胺基热固性塑料在紫外线交联和热脱交联的多次循环过程中的内在可回收性。硫代马来酰亚胺的热可逆光二聚化为动态聚合物网络的设计者提供了新的玩法,为共价交联材料的再加工和闭环回收提供了有趣的机会。
Thermoreversible [2 + 2] Photodimers of Monothiomaleimides and Intrinsically Recyclable Covalent Networks Thereof
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 °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.
期刊介绍:
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