Liquid Crystalline Vitrimers with Full or Partial Boronic‐Ester Bond Exchange
Liquid Crystalline Vitrimers with Full or Partial Boronic‐Ester Bond Exchange
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DOI：
10.1002/adfm.201906458
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发表时间：
2019-10
影响因子：
19
通讯作者：
M. Saed;Alexandra Gablier;Eugene M. Terentejv
中科院分区：
文献类型：
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作者：
M. Saed;Alexandra Gablier;Eugene M. Terentejv
在这份手稿中，一种新的玻璃体化学策略（硼酸酯交换）被引入到液晶弹性体（LCE）中，以允许无催化剂的键交换，从而能够在液晶（LCE）相中进行加工（指向矢对准，重塑和焊接）。此外，还探索了部分硫酸盐网络的概念，其中网络的一部分保持永久交联，从而保持材料的完整性并防止大的蠕变。这种组合策略允许避免当前对齐LCE方法的缺点，特别是在复杂形状中。硫醇-丙烯酸酯迈克尔加成反应用于生产具有可控热机械响应和局部塑性的均匀聚合物网络。塑性的控制是通过改变永久性和可交换网络的分数来实现的，其中具有最佳弹性/塑性平衡的材料“甜蜜点”被确定。这种可交换LCE（xLCE）允许进行后聚合处理，同时还最大限度地减少驱动期间不必要的蠕变。此外，在单个共价键合的复合结构中结合多种材料（各向同性和液晶）会产生各种智能变形系统，这些系统采用具有复杂曲率的形状。重塑和焊接xLCE可以使这些材料作为机械致动器应用于可逆折叠折纸、体内人造肌肉和软机器人中。
In this manuscript, a new vitrimer chemistry strategy (boronic transesterification) is introduced into liquid crystal elastomers (LCEs) to allow catalyst‐free bond exchange to enable processing (director alignment, remolding, and welding) in the liquid crystalline (nematic) phase. Additionally, the concept of partial vitrimer network is explored, where a percolating fraction of the network remains permanently cross‐linked, hence preserving the integrity of the materials and preventing large creep. This combined strategy allows one to avoid the shortcomings of current methods of aligning LCE, especially in complex shapes. Thiol‐acrylate Michael addition reaction is used to produce uniform polymer networks with controllable thermomechanical response and local plasticity. Control of the plasticity is achieved by varying the fractions of permanent and exchangeable network, where a material “sweet spot” with an optimum elastic/plastic balance is identified. Such exchangeable LCE (xLCE) allows postpolymerization processing, while also minimizing unwanted creep during actuation. Moreover, conjoining multiple materials (isotropic and liquid‐crystalline) in a single covalently bonded composite structure results in a variety of smart morphing systems that adopt shapes with complex curvature. Remolding and welding xLCEs may enable the applications of these materials as mechanical actuators in reversibly folding origami, in vivo artificial muscles, and in soft robotics.