Extrudable Covalently Cross-Linked Thio-Urethane Liquid Crystalline Elastomers
Extrudable Covalently Cross-Linked Thio-Urethane Liquid Crystalline Elastomers
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可挤出共价交联硫代氨基甲酸酯液晶弹性体
DOI：
10.1002/adfm.202307202
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发表时间：
2023
影响因子：
19
通讯作者：
Saed M
中科院分区：
文献类型：
--
作者：
Saed M
通过动态共价键（xLCE）交联的液晶弹性体网络具有在高温下塑性流动期间被（再）加工的显著能力，同时还允许其局部排列的（再）编程。然而，当前一代的xLCE不能直接挤出成细丝或注塑成能够致动的形状。在这里，提出了一种新型的聚（硫代氨基甲酸酯）（PTU）LCE热固性材料。包含二月桂酸二丁基锡作为催化剂使得能够通过两种不同的途径操纵弹塑性转变。硫代氨基甲酸酯键之间形成单独的硫醇和异氰酸酯的解离平衡交换与硫代氨基甲酸酯和游离异氰酸酯或硫醇基团的缔合交换竞争。快速塑性流动开始的温度为160 ° C，相关的键交换活化能为154 kJ mol−1。在弹性-塑性转变下的氢键使得弹性体坚固且极具延展性，其失效应变超过600%且海岸硬度A为72，从而防止循环热致动期间的任何蠕变。这种动态交联弹性体的多功能性通过使用商业双螺杆挤出机挤出，注塑成型为所需形状，并热压成平膜或形状而得到成功证明。
Liquid crystalline elastomer networks cross‐linked by dynamic covalent bonds (xLCEs) possess the remarkable capability of being (re)processed during plastic flow at high temperatures, while also allowing for the (re)programming of their local alignment. However, the current generation of xLCEs cannot be extruded directly into filaments or injection‐molded into shapes capable of actuation. Here, a novel poly(thio‐urethane) (PTU) LCE thermoset is presented. The inclusion of dibutyltin dilaurate as a catalyst enables the manipulation of the elastic–plastic transition through two distinct pathways. The dissociative equilibrium exchange between the thio‐urethane linkage to form separate thiol and isocyanate competes with the associative exchange of thio‐urethane and a free isocyanate or thiol groups. The temperature of fast plastic flow onset is ≈160 ˚C, and the associated bond‐exchange activation energy is ≈54 kJ mol−1. The hydrogen bonding below the elastic‐plastic transition makes the elastomer robust and extremely ductile with a failure strain exceeding 600% and a Shore hardness A of 72, preventing any creep during cyclic thermal actuation. The versatility of this dynamically cross‐linked elastomer is successfully demonstrated by extruding it using a commercial twin‐screw extruder, injection molding it into required shapes, and hot‐pressing it into flat films or shapes.