Title: A Facile Strategy for the Development of Recyclable Multifunctional Liquid Crystal Polymers via Post-Polymerization Modification and Ring-Opening Metathesis Polymerization

Author: Xin Zhao, Yan Chen, Bo Peng, Jia Wei*, Yanlei Yu*

Journal: Angew. Chem. Int. Ed., 2023, 62(21), e202300699

Abstract:

Post-polymerization modification (PPM) offers a versatile approach for engineering multifunctional polymers, but this advantage has not been fully exploited to fabricate multifunctional liquid crystal polymers (LCPs). Here, we design a facile synthetic approach towards multifunctional LCP by combining the ring-opening metathesis polymerization (ROMP) with PPM, in which ROMP helps to prepare a reactive LCP precursor with high molecular weight, and PPM provides a facilitation to introduce functional groups into the precursor. Consequently, a photo- and humidity-responsive linear LCP (LLCP) is demonstrated to show the potential of this synthetic strategy to diversify functions of the LCPs. Under light irradiation and humidity changes, the deformation modes of the LLCP films are converted to complex shapes (bending, twisting, and curling). The obtained dual-responsive LLCP with high molecular weight possesses excellent processability and recyclability, making it possible to construct 3D shape actuators with programmable deformation behaviors under light/humidity.

论文链接：https://onlinelibrary.wiley.com/doi/10.1002/anie.202300699

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论文速递：

  本文首次结合开环易位聚合（Ring-Opening Metathesis Polymerization, ROMP）与聚合后修饰（PPM）以制备多功能性液晶聚合物（图1a）。通过ROMP可以得到高分子量反应性线型液晶聚合物前驱体PABPFP（图1b），使其无需交联即可展现出良好的力学强度以及光致形变能力。同时，借助PPM在前驱体反应性位点上精确引入所需功能基团，为响应性液晶聚合物的多功能化衍生提供便捷的制备途径。利用这种通用型策略制备了可回收光湿双响应线型液晶聚合物（PABCOOH），并通过机械热拉伸法制备得到了具有良好液晶取向的薄膜材料（图1e，f）。

图1.（a）光湿双响应液晶聚合物合成路线；（b-d）响应性液晶聚合物与其前驱体的分子量测定、核磁共振氟谱及热力学性质表征；（e）响应性液晶聚合物薄膜制备过程及取向机理展示；（f）2D-XRD表征

  该薄膜在紫外光照射下，表面的偶氮苯分子由trans异构体转变为cis异构体，使该薄膜沿着液晶基元排列方向弯曲，而cis异构体在可见光照射下可回复到trans异构体，使薄膜回复到平整状态。此外，聚合物薄膜中羧酸基团主要以氢键二聚体形式存在，当其在碱处理后，氢键网络被破坏并转化为吸湿性羧酸盐网络，当环境相对湿度增加后，薄膜可吸水膨胀并沿着垂直于液晶基元排列方向弯曲。

  得益于该液晶聚合物材料的线型结构，可以对薄膜进行三维塑形与回收，通过折纸、裁剪等方法制备了仿生“海葵”三维执行器，展示了其在紫外光和湿度刺激下的各向异性形变行为，并彰显了这种材料良好的回收性。该策略为多重刺激响应材料分子结构的丰富化提供有力的支持，有助于多重响应功能、可控形变方向的仿生三维执行器的构筑，及其在智能软机器人等领域的潜在应用。

图2.（a）自然界中的海葵示意图；（b）仿生“海葵”三维执行器的制备过程及（c）在紫外光与湿度变化下的形变过程

   该研究成果作为Hot Paper发表于Angew. Chem. Int. Ed., 2023, 62(21), e202300699。