基于多巴胺-金属动态配位键的可水下自修复憎水性聚合物

This proposal aims at developing hydrophobic polymer solids that can be repeatedly healed under water. The polymers consist of hyperbranched polyurethane and epoxy resins that are crosslinked by DOPA–metal ions coordinate bonds. To promote the diffusion and collision of molecular chain in the water, a certain amount of hydrophilic groups were grafted on the molecular chain ends of hyperbranched polymers. Consequently, underwater self-healing and recycling of polymer materials can be yielded due to overcoming of the shielding effect of water between hydrophobic polymers. When the polymer is damaged in seawater, reshuffling of the hyperbranched polymer networks across the crack interface, owing to the dynamic DOPA-Fe3+ crosslinkages activated by water, rebinds the damaged site. This process is not sensitive to the pH value of the water. By taking advantage of the same mechanism, the polymer can also be remolded with the help of seawater and the recycled polymer is still self-healable in seawater. Meanwhile, the performance of the material itself can be conveniently adjusted by changing the content of hydrophilic groups as well as the structure and flexibility of hyperbranched chains. We will focus on molecular design, synthesis approaches and self-healing mechanism, etc. It is believed that water triggered dynamic feature of coordination bond and its influence on the self-healing process will be revealed. The effects of hyperbranched polymer molecular structure, DOPA–metal ions coordinate bonds, the hidden hydrophilic group, etc. on the mechanical properties and underwater self-healing will be illuminated. Based on these researches, this kind of polymer structure and performance will be optimized. On the whole, this project will provide deeper understanding about underwater self-healing of hydrophobic polymers solid.

基于我们最近发现的多巴胺-金属离子配位键在水中具有动态可逆性这一新现象，本项目拟在超支化聚合物分子链端引入该配位键，利用前者大量的支链，构筑富含多巴胺-金属离子配位键的交联网络，发展一种可在较宽pH范围（7~9）水下反复多次自修复的结构用憎水性聚合物。为突破水屏蔽憎水性聚合物断面间重新键接的障碍，还将引入适量隐藏亲水基团，在保证目标聚合物憎水性的同时，使其在水中损伤后，断面上分子链能相互扩散和碰撞，进而通过水激发配位键的交换以及网络重排，实现断面的配位键链接、愈合裂纹，恢复材料的承载能力。本项目将深入开展分子设计、合成方法与修复机理研究，揭示水激发配位键的动态反应规律及其对修复过程的影响，阐明超支化聚合物的分子结构、各种多巴胺-金属离子配位作用、隐藏亲水基团等与材料力学性能和水下自修复性的相关性。在此基础上，优化此类聚合物的结构与性能，为将自修复型聚合物拓展至不同水环境中应用提供科学依据。

在海洋环境中，由于海水侵蚀和应力作用，使应用于海水中的高分子材料很容易损坏，减少了这些材料的使用寿命，因此，赋予聚合物材料水下自修复能力是解决该问题的方法之一。然而，到目前为止，有关结构用聚合物材料的水下自修复研究报导很少，主要是缺乏合适的自修复策略。受贻贝足丝在水下有很强粘附性的启发，我们发现多巴-铁配位键是海水激发的可逆键，为此设计了一种超支化聚合物，将多巴胺引入超支化聚合物端基，再利用多巴胺与Fe3+或硼酸反应生成配位化合物Fe[DOPA]3或硼酸酯来交联聚合物，同时，在聚合物的端基引入少量的亲水基团，以促进聚合物断面上憎水的聚合物分子链在水中发生相互扩散与碰撞，利用多巴-金属离子配位交联键的动态作用，以实现聚合物材料的水下自修复。开展了分子设计、合成方法，配位键动态反应的规律与修复机理方面的基础研究，为建立这种具有水下自修复能力的新型聚合物提供科学依据。. 研究结果表明，水激发儿茶酚-金属离子配位键发生动态可逆反应，并伴随着聚合物交联网络的重排，使得材料断面两侧相互扩散的分子链形成新的配位键交联，跨越断面“缝合”裂纹，实现修复。该聚合物在人造海水中具有自修复能力，使薄膜表面的划痕在浸泡24小时后消失，而切断的拉伸样条在海水中也几乎可完全恢复原有的力学性能，修复效率可以达到93.5%。剪切测试表明，这种超支化聚氨酯具有多次重复修复能力。利用剪碎样品水下回收实验，进一步证明水激发配位键的交换反应，可诱导聚合物网络的重排，从而粘结裂纹。本项目不仅在憎水性聚合物海水下可逆自修复方面取得了突破，而且在硼酸酯的超支化聚合物中引入叔胺，使其在中性和碱性水环境中均具有较好的修复效果。相关研究思路未见报导，对于推动水下本征自修复固体材料的基础研究和实际应用具有重要价值。