用于单分子力化学的多重力学旁路高分子

Mechanophores in a polymer are susceptible to chemical change caused by mechanical triggers. These mechanophores possess a huge potential in various applications, such as stress sensors, fault localization and self-healing materials. In recent years, polymer mechanochemistry has been emerged in the developing areas, urged researchers to design and synthesize new mechanophores, to explain the reason of some changing reactivity rules or trends and to find new reactions accelerated by force. . In this project, we plan to apply atomic force microscope (AFM) based single-molecule force spectroscopy (SMFS) to investigate the mechanical and physicochemical properties of mechanophores in a single polymer chain. . Firstly, we’ll synthesize a “mechanical bypass repeating unit”, which will be incorporated by a Dynamic Covalent Bond in a short path and a PEG loop (occupying a long path) on the side. Then, metal catalyst based polymerization methods Acyclic Diene METathesis (ADMET) and Ring-Opening Metathesis Polymerization (ROMP) will be used to synthesize “Multiple Mechanical Bypass Polymer” (MMBP) for SMFS experiments. Three different dynamic covalent bonds, including thiol-maleimide, furan-maleimide and anthracene dimer will be studied. In SMFS experiments, MMBP will be anchored to both of substrates and AFM tips. The increasing tensile force can achieve the fracture point and break the dynamic covalent bonds in polymer backbone. The bypass loop will be mechanically adjusted by force orientation, prolongs the polymer backbone. The procedure creates a plateau, which means break of the dynamic covalent bond same as fingerprint spectroscopy. The design of polymer can significantly improve sampling efficiency and the accuracy of force detection (resolution ~10-20 pN). Previously, the traditional statistical method to distinguish the isomers had constraints but it has been possible now. . Furthermore, force orientation and torque can be precisely controlled by the shape and anchor position present in mechanophores as well as polymer structures. By the synthesis of a series of model anthracene dimers, SMFS experiments and computing techniques, we may reveal at least a part of, the relationship between bond break, torque, pulling direction, free energy landscape, and force-triggered chemical reaction pathway.. By using MMBP, we will deliver a general experiment setup for high efficient and precise force detection of dynamic covalent bonds. We believe these mechanism-oriented experiments and valuable conclusions will contribute to the fundamentals of mechanochemistry and benefit the scientific community of single-molecule mechanics.

使用机械力能够激活高分子材料中的“力响应基团”（Mechanophore）发生化学反应，这种特性有望在压力传感，材料探伤和自修复材料中发挥作用。近年来高分子力化学领域发展迅速，新发现频出，吸引研究人员寻找新型力响应基团，并研究一些“反常”的力化学现象。本项目拟采用基于原子力显微镜的单分子力谱，在分子层面研究单根高分子链上力响应基团的力学性能和理化特性。首先，我们运用控制性聚合制备多重力学旁路高分子，将包括巯基—马来胺、呋喃—马来胺和二聚蒽在内的“动态化学键”纳入研究范畴，该设计极大地提高单分子力谱测量的效率和精度（力学分辨率可达到10-20 pN），并为动态化学键的解离提供指纹谱，可用于测量力响应基团的不同构型。除此之外，合理地设计力学旁路高分子，能精确控制施力方向和扭矩大小，结合拉伸—回复实验和化学计算，为探索不同力化学反应路径提供了可能，促进力化学领域的技术开发和理论进步。

以力学为线索，基于单分子力谱技术及力学水凝胶材料，我们揭示了疏水相互作用的尺寸依赖性，疏水相互作用在20nm范围内发挥作用，在10nm内指数衰减，根据Lum-Chandler-Weeks（LCW）理论，疏水粒子的水合过程与其尺度有关，当粒子尺度较小时（<1nm），水合过程是体系的熵驱动的，更大时（>1nm），水合过程是由体系的焓驱动的。我们通过单分子力谱技术，以单根聚苯乙烯为模型，首次从实验上测量了疏水界面自由能的尺寸依赖性，验证了LCW理论，启发了通过尺寸依赖性来调控疏水相互作用强弱的新思路；研究了马来酰亚胺—巯基的力化学特性，这是一类动态化学键，我们发现其加成物硫代丁二酰亚胺的水解受力依赖的动力学控制机制，仅通过施加力就实现了反应路径的改变，当施加的力超过270pN的阈值，丁二酰亚胺的五元环水解占主导地位，从而形成稳定的水解产物，为提升抗体偶联药物稳定性提供了简洁的方案；研究了力学模量在干细胞干性保持中的作用，利用β-环糊精和马来酰亚胺的相互作用，进一步增加了与自由巯基的反应自由能，调节了制备胶体的力学模量均匀度，发现力学不均匀水凝胶适合维持干细胞的干性而力学均匀水凝胶有助于干细胞的成骨分化；通过多非共价金属离子—配体相互作用，以此为交联点，实现了热力学稳定，动力学良好的可注射水凝胶，为合理调整可注射水凝胶的动力学和力学性能提供新方法。