自增强力致变色材料的设计合成与性能研究

Polymers that change their properties upon application of external stimuli such as light, heat, pH, or redox potential are now ubiquitous. However, the smart materials using mechanical force as stimuli is blossoming, which have great applications in mechanical sensor, safety communication, human motion monitor, etc. Although current systems can change their color for early warning at stress concentration area, they cannot feedback to this kind of potentially destructive force. Therefore, the design and synthesize of mechanochromic materials need to propose new ideas. In this project, beginning from the relationship between molecular structure and performance, the mechamochromic material will be endowed with response-feedback mechanism through an ingenious combination of color change unit and self-strengthen unit. In the first strategy, the color change unit and dihalogenated cyclopropane derivates will be introduced to the polymer chains in series. By rational structure design, the breaking energy of weak bonds in the two kinds of force sensitive units can be optimized. In the second strategy, the color change unit and dihalogenated cyclopropane derivates were introduced to the polymer chains in parallel. No matter of the breaking energy of weak bonds in color change unit match with self-strengthen unit, the unique cyclic structure can ensure the order of response and feedback behavior. Based on the investigation on the different systems of the force sensitive unit and polymerization, we can disclose the relationship between structure and performance of material. We will develop new strategy and method for preparation of self-strengthen mechanochromic materials through the study of this project.

以光、热、pH或氧化还原电位为刺激源的刺激响应聚合物目前已普遍存在。而以力为刺激源的新型智能材料正方兴未艾,其在力学传感，安全通信及人体运动监测等领域都有着巨大的应用价值。目前报道的体系可以对过载应力起到变色预警作用，但无法反馈这种潜在的破坏性应力。因此，力致变色聚合物的设计合成需要有新思路。本项目将从分子结构与性能的关系出发，通过变色基团和增强结构的巧妙结合赋予材料以响应-反馈机制。第一种策略是将变色单元与二卤代环丙烷类结构串联引入到分子链中。通过结构的合理设计和调控，优化两种结构中弱键的断裂键能。第二种设计策略是将变色单元和二卤代环丙烷类结构并联成环。无论两种结构单元中弱键键能是否匹配，这种特殊环状结构本身就确保了响应-反馈机制发生的先后次序。基于对力响应基团体系和聚合体系的对比研究，揭示结构和材料性能之间的关系。通过本项目的研究可以为制备自增强力致变色聚合物材料提供新的策略和方法。

在自然界中，生物组织通常能感知到机械损伤并自发地进行修复。受此现象的启发，化学家们致力于赋予合成聚合物以类似的性质，即对聚合物材料的损伤部位进行传感并采取措施延长其使用寿命。然而，这方面的研究工作目前仍处于初级阶段。本项目从分子结构与性能的关系出发，通过变色基团和增强结构的巧妙结合赋予材料以响应-反馈机制。为此，首先开发了一种可区分高低应力的多色转换力致变色弹性体。结果发现，弹性体在低的拉伸应力下（＜ 1.8 MPa），可以观察到能够发出蓝色荧光蒽衍生物的形成。而在高的拉伸应力下（＞ 1.8 MPa），蒽-马来酸酐加成物（AMA）和罗丹明衍生物（RH）都会被应力激活。因此，TN0.5AMA/0.4RH弹性体表现出蓝白色至红色荧光的转变现象。由于多次溶胀聚合，第一重网络的分子链相对舒展。材料受力时，其首先受力，而相对卷曲的第二重网络分子链则需要在较大的应力下才会受到明显的拉伸作用。在TN0.25AMA+0.25RH对照弹性体中，由于AMA和RH都在第一重网络分子链中，这两种力致变色基团因此会同时受力。这种不同应力程度下宏观荧光颜色的转变行为能够有效地显示出材料中的应力集中区域，将有利于材料断裂机理的深入研究。接着，我们构筑了一种新型的环丁烷衍生物力致变色基团（NCD），并以其制备了一种自增强力致变色聚合物P1。机械刺激P1中的NCD会导致其发生反[2+2]环加成反应，形成trans,trans构型的肉桂酸二聚体。由于肉桂酸二聚体结构共轭程度的增强，位于423 nm处荧光发射峰的强度显著增加。在紫外光或可见光的照射下，肉桂酸二聚体中的C=C双键会发生分子间的交联反应，MTP的杨氏模量和拉伸强度因此分别增加为原先的1.5倍和1.6倍。这些结果充分地表明P1是一种可用于材料损伤预警和智能自增强用途的理想材料。