The growing demand for smart polymeric transducers such as dielectric elastomer actuators and energy harvesters has urged the use of sustainable and recyclable elastomeric materials. Vitrimer chemistry has shed light on future reprocessable and recyclable thermosets and elastomers. In this work, epoxidized natural rubber (ENR) vitrimers were prepared using diacid or triacid cross-linkers and formed covalently cross-linking networks via thermally triggered reversible β-hydroxy ester bonds. The cross-linked ENR elastomers exhibited Arrhenius-type viscoelastic behavior with a complete stress relaxation between 140 and 160 °C, that is, vitrimer characteristics, which were highly dependent on the cross-linking temperature. The mechanical and dielectric properties of the ENR vitrimers can be tuned by varying the molecular structure and concentration of the cross-linkers. Among the diacid and triacid cross-linkers, Pripol 1017 fatty polyacid (P1017) and 3,3′-dithiopropionic acid (DTPA) had similar effects on the cross-linking density and mechanical properties of the ENR vitrimers. The highest tensile strength of 8.70 ± 1.9 or 15.6 ± 2.6 MPa was obtained at 6 mol % of P1017 or DTPA, respectively. While for diamide-based diacid cross-linker (DME), 8 mol % was needed to reach the highest tensile strength of 13.1 ± 2.7 MPa for the elastomer. The three ENR vitrimers showed increased relative permittivity ε′ = 5∼7 at 1 kHz while maintaining low dielectric losses compared to traditional dicumyl peroxide-cured ENR, with ε′ = 3.57 at 1 kHz. With the optimized acidic cross-linker concentrations of P1017 at 6 mol %, DTPA at 6 mol %, and DME at 8 mol %, the ENR vitrimers exhibited improved actuation capabilities at lower electrical fields. Utilizing dynamic cross-linkers to tune the electromechanical properties of dielectric elastomers and the reversibly cross-linked polymer networks will open new opportunities for smart and sustainable dielectric elastomer devices.

中文翻译：

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通过交联剂调整天然橡胶 Vitrimers 的机电性能

对介电弹性体致动器和能量收集器等智能聚合物换能器的需求不断增长，这促使人们使用可持续和可回收的弹性体材料。Vitrimer 化学为未来可再加工和可回收的热固性塑料和弹性体提供了启示。在这项工作中，使用二酸或三酸交联剂制备环氧化天然橡胶 (ENR) 玻璃体，并通过热触发的可逆 β-羟基酯键形成共价交联网络。交联的 ENR 弹性体表现出 Arrhenius 型粘弹性行为，在 140 至 160 °C 之间具有完全的应力松弛，即高度依赖于交联温度的 vitrimer 特性。ENR 玻璃体的机械和介电性能可以通过改变交联剂的分子结构和浓度来调节。在二酸和三酸交联剂中，Pripol 1017 脂肪多酸 (P1017) 和 3,3'-二硫代丙酸 (DTPA) 对 ENR 玻璃体的交联密度和机械性能具有相似的影响。分别在 6 mol% 的 P1017 或 DTPA 下获得了 8.70 ± 1.9 或 15.6 ± 2.6 MPa 的最高拉伸强度。而对于基于二酰胺的二酸交联剂 (DME)，需要 8 mol% 才能使弹性体达到 13.1 ± 2.7 MPa 的最高拉伸强度。与传统的过氧化二异丙苯固化的 ENR 相比，三种 ENR 玻璃体在 1 kHz 时显示出增加的相对介电常数 ε' = 5∼7，同时保持较低的介电损耗，在 1 kHz 时 ε' = 3.57。使用 6 mol% 的 P1017、6 mol% 的 DTPA 和 8 mol% 的 DME 的优化酸性交联剂浓度，ENR 玻璃体在较低电场下表现出更好的驱动能力。利用动态交联剂来调节介电弹性体的机电性能和可逆交联的聚合物网络将为智能和可持续的介电弹性体设备开辟新的机遇。