物理交联的主链型光致形变液晶聚合物体系的构筑及其性能研究

This project aims to develop advanced photodeformable main-chain liquid crystalline polymer (LCP) systems with physically crosslinked networks. A series of azobenzene (azo)-containing main-chain LCPs with secondary amino groups or/and amide groups in their backbones are to be prepared by using Michael addition polymerization and Michael addition-amidation cooperative polymerization techniques, from which advanced photodeformable materials with the combined advantages of main-chain LCPs (i.e., high alignment coupling ability between the mesogenic units and polymer chains) and physically crosslinked polymers (i.e., high recyclability and reprocessibility) as well as excellent film and fiber-forming capabilities will be developed by utilizing either the controlled polymerization-based post-modification approach (to introduce flexible polymer side-chains to the main-chain LCPs to form entanglement crosslinking), or the blending strategy with other functional polymers (e.g., those containing carboxyl groups) (to generate hydrogen bonding-induced crosslinking systems), or by further introducing functional nanoparticles into the above two systems (to improve their mechanical or other properties). The synthetic conditions for the above azo polymers will be optimized, and the properties of photodeformable polymer systems with different physical crosslinking mechanisms (i.e., macromolecular entanglement crosslinking or hydrogen bonding-induced crosslinking) will be compared. In addition, the effects of the structures of the azo polymers (such as the kinds and densities of the hydrogen bonding-forming groups in their backbones as well as the chemical structures and molecular weights of the grafted flexible polymer side-chains) and the structures and contents of the blended materials on the physical and mechanical properties and photomechanical behaviors of the photodeformable systems will be investigated in detail. The above studies will provide theoretical and practical basis for the development of advanced photodeformable materials. This project opens up facile and efficient new ways for the generation of photodeformable polymers with outstanding comprehensive performance and is thus of significant scientific importance.

本项目以发展物理交联的高性能主链型光致形变液晶聚合物体系为目标。拟利用迈克尔加成聚合与迈克尔加成-酰胺化协同聚合技术制备一系列含仲胺或/和酰胺基团的主链型偶氮液晶聚合物，并通过可控聚合后修饰方法(引入柔性高分子侧链以形成物理缠结)或与其他功能高分子(如含羧基者)共混策略(形成氢键交联体系)，或进一步在上述体系中引入功能性纳米粒子的方法，得到兼具主链液晶聚合物的高取向偶合性与物理交联体系的可回收再加工性、且拥有优异成膜/成纤能力的高性能光形变材料。优化聚合物的制备条件，比较不同物理交联(高分子链缠结与氢键交联)光形变体系的性能，研究聚合物结构(如主链上可形成氢键的基团种类与密度及高分子侧链的结构与分子量等)及共混材料结构与含量对光形变体系物理机械性能与光机械行为的影响，为发展高性能的光形变材料提供理论与实验依据。上述研究为制备具有优异综合性能的光致形变聚合物开辟了新途径，具有重要的科学价值。

兼具主链型液晶聚合物的高取向偶合性与物理交联体系的可回收再加工性、且拥有优异成膜/成纤能力的物理交联主链型光致形变偶氮聚合物在光制动领域具有广阔的应用前景，因此发展高效制备此类主链型光致形变偶氮聚合物的方法具有重要的意义。本项目瞄准上述科研目标展开工作，取得了如下主要研究成果：(1)利用迈克尔加成聚合与迈克尔加成-酰胺化协同聚合技术，成功制备了一系列骨架中含有可形成氢键的功能基团(包括仲胺基或/和酰胺基、脲基)的主链型光致形变偶氮聚合物。通过系统的聚合条件优化，得到了高效合成高分子量的主链型偶氮聚合物的途径，解决了利用迈克尔加成聚合所得主链型偶氮聚合物分子量低难以成膜的挑战性难题。(2)进一步通过可控聚合后修饰方法在主链型偶氮聚合物中引入柔性高分子侧链以形成物理缠结，或在主链型偶氮聚合物中掺入聚多巴胺纳米粒子的方法，发展了制备光形变聚合物的新物理交联机理，并构筑了兼具紫外/可见光化学响应与近红外光热响应的光形变复合体系。(3)通过系统的结构-性能关系研究，得出了物理交联的主链型光致形变偶氮聚合物体系的最佳结构参数和一些具有普遍意义的规律，并最终获得了具有优异成膜/成纤性能与高机械强度、可在室温下再塑形、再加工与光形变、或/与拥有加热愈合或(由近红外光引发的)自焊接能力的高性能光形变材料。(4)还对利用本课题组发展的“后交联策略”制备的光致形变偶氮聚合物体系的结构-性能关系进行了系统研究，并通过将含有二硫键的二胺交联剂引入该“后交联策略”的方法，成功发展了简便高效地制备具有化学交联结构但可回收再利用的光致形变偶氮聚合物的新途径。上述工作为制备具有优异综合性能的主链型光致形变偶氮聚合物开辟了新途径，并为进一步发展高性能的光形变聚合物提供了重要的理论与实验依据，所得光形变偶氮聚合物在软体机器人、人工肌肉及微流体器件等领域具有重要的应用前景。上述研究成果成功实现了本项目的预定目标。

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