协同氢键作用构筑具有极优异力学性能的水凝胶材料

Hydrogels are typical wet and soft materials, but the mechanical properties of normal synthetic gels are extremely poor. Since the beginning of this century, many kinds of hydrogels with high mechanical strength have been developed, but their mechanical properties are far inferior to those of the tendons and ligaments, which are mainly cross-linked by physical interactions. Based on the understanding of the new definition of hydrogen bonding and the nature of hydrogen bonding, especially cooperative hydrogen bonding and its formation criteria, we propose to carry out a series of work on the development of hydrogels with extraordinary mechanical properties based on cooperative hydrogen bonding interactions. By selecting appropriate polymers and small molecules as hydrogen bond donors and acceptors, and developing novel methods, including self-assembly, mixing-drying-swelling, cold drawing and in situ reaction or polymerization under stretching, to enhance the cooperative hydrogen bonding in a gel network, a variety of hydrogels with high mechanical strengths can be prepared. Through the study of their structures and mechanical properties, it is expected to further improve the mechanical properties of the gels and obtain hydrogels with mechanical properties superior to those of biological tissues and even some dry and hard materials (e.g. plastics). In addition, tough and strong hydrogels with self-healing and shape memory behaviors can also be obtained by adjusting the composition of strong and weak hydrogen bonds in the gels. This study will help people to make better use of hydrogen bonding to prepare polymeric materials with excellent properties.

水凝胶是典型的湿、软材料，但普通合成凝胶的力学性能极差。自本世纪初，很多种具有高机械强度水凝胶已被开发出来，但其力学性能在很多方面远不如主要由物理作用交联的肌腱、韧带等生物组织。基于对氢键新定义和对氢键性质尤其是协同氢键作用及其形成条件的理解和认识，我们拟开展一系列基于协同氢键作用构筑具有极为优异机械性能水凝胶方面的工作。选取适当的高分子和小分子化合物作为氢键供体和受体，并采用自组装、混合-干燥-溶胀、冷拉和在保持凝胶拉伸状态下原位反应或聚合等创新方法来增强凝胶网络中的协同氢键作用，制备出多种高机械强度水凝胶。通过对凝胶结构和性能的深入研究，有望进一步改善凝胶性能并得到力学性能超过生物组织甚至一些干、硬材料（如塑料）的水凝胶材料。另外，通过调控凝胶中强、弱氢键的构成，还可以得到具有自愈性和形状记忆性的高机械强度水凝胶。本研究将有助于人们更好地利用氢键制备具有优异性能的高分子材料。

水凝胶是典型的湿、软材料。自本世纪初，很多种具有高机械强度水凝胶已被开发出来，但其力学性能在很多方面远不如主要由物理作用交联的肌腱、韧带等生物组织。基于对氢键新定义和对氢键性质尤其是协同氢键作用及其形成条件的理解和认识，我们开展了一系列基于协同氢键作用构筑具有极为优异机械性能水凝胶方面的工作。开发了多种基于氢键交联作用的高强度水凝胶的制备方法,包括冷拉法、拉伸冷冻解冻法以及定向冷冻解冻-拉伸冷冻解冻法制备具有各向异性结构和优异力学性能的水凝胶；固相酯化法和混合-干燥-溶胀法等增强氢键作用或同时引入化学交联提高凝胶的力学性能；盐析法、盐析和拉伸结合法促进氢键作用制备高强度水凝胶；氢键和金属离子配位共同构筑高强度凝胶等方法。冷拉法制备的聚乙烯醇/聚丙烯酸水凝胶的拉伸强度和弹性模量分别达到140 MPa和100 MPa，韧性和断裂能分别达到117 MJ m-3和101 kJ m-2，远超已报道的高强度水凝胶、生物组织甚至工程塑料。制备了具有优良抗菌性的各向异性聚乙烯醇-单宁酸水凝胶和具有金属离子响应性和激发波长依赖性的非传统多色荧光水凝胶用于信息加密，开发了基于静电作用和氢键的水凝胶高强粘合方法，开发了划痕法及光刻图案法改变凝胶表面积以驱动水凝胶发生可控复杂变形。对所得的各种水凝胶的结构和性能关系进行了深入的探讨，同时对各种凝胶体系中的氢键作用及其影响因素进行了研究。这些工作证明拉伸、冷冻解冻、干燥和盐析处理等方法都有利于氢键甚至协同氢键的形成，其原因是在外力驱动下，聚合物之间或聚合物-小分子化合物之间距离减小并更有利于采取适当的构象形成强的氢键作用甚至驱动化学反应的发生。本项目的研究结果将有助于人们更好地理解氢键作用并利用氢键制备具有优异性能的高分子材料，满足各种领域应用的需求。