双智能凝胶材料的可控构建及其温敏与自修复协同机制

Aimed at the demand of multi-intelligence and high performance of smart materials, this project takes temperature-sensitive poly (N-isopropyl acrylamide) (PNIPAM) as the research object. Base on the method of host-guest self-assembly between β-cyclodextrin (β-CD) and adamantane (Ad) and the design concept of reticular chemistry, controllable Ad-ended multi branched star-type oligomer "knot" and β-CD-ended double branched line-type oligomer "rod" are designed and prepared to construct dual-intelligent hydrogel of both temperature-sensitivity and self-healability. Taking advantage of the even-distributed physical join points, the temperature-sensitive hydrogel can be endowed biomimetic self-repairing function, more importantly, in virtue of the cooperative action of temperature-sensitivity, the self-healable hydrogel can even realize automatic self-healing of not only micro-cracks but also macroscopical large cracks. By intensive studying of the controllable construction and structure-activity relationship between structure and temperature-sensitivity, mechanical property and self-healing performance for the dual-intelligent hydrogels, and key researching of the coordination mechanism between temperature-sensitivity and self-healing performance and self-healing enhancing principle, this project will ultimately contribute to provide systematical guide and reference for development of dual-intelligent soft materials with fast environmental-response, excellent mechanical property and macroscopical large crack self-healability, as well as for coordination and enhancement of dual intelligences.

针对智能材料朝向多智能化和高性能化方向发展的需要，本项目以温敏性聚(N-异丙基丙烯酰胺)（PNIPAM）为研究对象的，采用β-环糊精(β-CD)和金刚烷(Ad)的主客体自组装的方法，结合框架化学的设计理念，设计并制备可控的多支星型低聚物金刚烷 “结”和双支线型低聚物β-环糊精 “杆”，进而以这两种基本单元构筑兼具温敏和自修复功能的双智能水凝胶。利用凝胶网络中均匀分布的超分子物理连接点，温敏性水凝胶被赋予仿生自修复的功能，并且借助温敏性的协同作用，该自修复水凝胶可实现不仅微裂纹而且宏观大裂纹的自动自修复。通过深入研究该双智能水凝胶的可控构建及结构与其温敏性、力学性能和自修复性能的构效关系，并重点研究该双智能水凝胶的温敏性与自修复性能的协同机制及自修复强化原理，本项目最终为发展具有快速的环境敏感性、优异的机械性能和宏观大裂纹自修复功能的双智能软材料及双智能性间的协同与强化提供系统的指导与借鉴。

自修复材料可以自动修复由于极端外部条件（如大变形或外力破坏）所引起的材料区域性损伤，从而延长材料的工作寿命和使用稳定性。然而迄今为止，现有报道的自修复材料，一般只可以实现微裂纹的自修复，而对于使材料断面两侧不接触的大裂纹，除非手工将其贴合在一起否则便无法完成自修复。因此，为了解决现有自修复材料在大裂纹自修复方面的弊端，本项目首次提出了利用温敏性水凝胶的体积膨胀和收缩效应来调控裂纹间距，从而实现本征自修复材料从微裂纹到大裂纹的自动自修复。首先，我们设计了末端为金刚烷基的四臂和六臂的温敏性聚N-异丙基丙烯酸酰胺（PER-(PNIPAM-Ad)4, DiPE-(PNIPAM-Ad)6）和末端为-环糊精的双臂线型温敏性聚合物（EG-(PNIPAM-βCD)2），通过活性聚合和点击反应实现了所设计聚合物单元的可控制备，进而通过两种单元末端基的主客体自组装分别在水溶中温和条件形成两种结构的超分子水凝胶。通过核磁、红外、GPC和SEM表征了凝胶的结构和形貌，进而通过示差扫描量热仪和流变仪研究了凝胶的温度响应性，以及采用大小形变交替循环的流变性能测试考察了凝胶的本征自修复性能，并且利用凝胶的温敏性和本征自修复性能通过肉眼观察和拉曼光谱研究了凝胶的大裂纹自修复性能及温敏性对自修复性能的协同机制，最后本项目还对材料的生物相容性进行了研究。结果表明，所制备的凝胶材料保持了明显的温度响应性，其体积相转变温度约为31-32oC; 在相转变温度上下均具有快速反复的微裂纹本征自修复性能，流变显示，在60s内其动态模量可100%恢复到起始值；结合凝胶的温敏性和自修复性能，实现了所制备材料的大裂纹自修复，考察条件下最高修复裂纹宽度可达到3mm(材料起始长度的10%)；另外，细胞毒性实验表明该凝胶材料没有明显的细胞毒性。实验结果验证了我们最初的设计假说，为新型结构多功能高智能凝胶材料的设计提供了新的设计思路，拓展了温敏性聚合物的应用范围和发展了材料自修复的理论，推动了智能凝胶材料在生物医学领域的应用。