School of Mechanical and Materials Engineering, Composite Materials and Engineering Center, Washington State University, Pullman, WA, 99164, USA.
College of Natural Resources, North Carolina State University, Raleigh, NC, 27607, USA.
Macromol Rapid Commun. 2019 Apr;40(7):e1800889. doi: 10.1002/marc.201800889. Epub 2019 Feb 5.
Epoxy vitrimers prepared from anhydride-cured epoxies exhibit, repairable and reprocessable properties; however, they generally rely on a large amount of catalyst for accelerating the dynamic transesterification (DTER). If the catalyst loading is not enough, the vitrimer properties will be limited. In this work, a preparation method of catalyst-free epoxy vitrimer is demonstrated by adding glycerol to an epoxy-anhydride curing system. The hydroxyls of glycerol first react with the anhydride to induce the ring-opening of anhydride and form a carboxylic acid, and the latter attacks the epoxy and form a β-hydroxyester linkage, so the curing can be performed in the absence of catalyst. A significant amount of hydroxy groups are preserved in the crosslinked network, and they serve as both reacting moiety and catalyst for the DTER, which imparts fast relaxation and satisfactory repairability to the materials. By taking advantage of this mechanism, a catalyst-free and self-healing coating is demonstrated. These findings provide a solution to avoid using catalyst in vitrimer preparation and advance the application of vitrimer in coating. However, the addition of glycerol produces a decrease of the T of the final materials, which needs to be further addressed in the future study.
由酸酐固化的环氧树脂制备的环氧型热塑弹性体表现出可修复和可再加工的性能；然而，它们通常依赖于大量的催化剂来加速动态酯交换反应（DTER）。如果催化剂的负载量不足，热塑弹性体的性能将受到限制。在这项工作中，通过向环氧树脂-酸酐固化体系中添加甘油，展示了一种无催化剂制备环氧型热塑弹性体的方法。甘油的羟基首先与酸酐反应，引发酸酐开环并形成羧酸，后者攻击环氧树脂并形成β-羟酯键，因此在没有催化剂的情况下也可以进行固化。大量的羟基残留在交联网络中，它们既是反应部分，也是 DTER 的催化剂，赋予材料快速的松弛和令人满意的可修复性。利用这一机制，展示了一种无催化剂和自修复的涂层。这些发现为避免在热塑弹性体制备中使用催化剂提供了一种解决方案，并推进了热塑弹性体在涂层中的应用。然而，甘油的添加会导致最终材料的 Tg 降低，这需要在未来的研究中进一步解决。
