规整网络高分子的应变诱导结晶机理

The structure and properties of semi-crystalline polymer materials are closely related to the external field during processing. Therefore, a deep understanding of the structural formation and evolution mechanism under external field is of great significance to guide the polymer processing and regulate the final performance of products. In the present project, a series of regularly crosslinked polyethylene glycol films with different crosslink densities will be prepared by using the preparation method of high-performance tetrahedral hydrogel. As a model network polymer, the strain-induced crystallization will be studied by means of synchrotron X-ray scattering technology. A quantitative relationship between strain-induced conformational entropy change and crystallization rate will be established. The relationship between the critical strain and the crosslink density of regular network polymer, and the effects of chain orientation, relaxation, and stress on the nucleation, growth, and morphology of network polymer crystals will be clarified. The mechanism of strain-induced crystallization will be revealed. The results will provide theoretical guidance for the processing of polymer materials and the preparation of self-reinforced materials.

半结晶高分子材料的结构和性能与加工过程中的外场作用密切相关，因此，深入研究高分子在外场下结晶结构的形成与演化机理对于指导高分子加工过程和调控产品的最终性能具有重要意义。本项目借鉴高强度类四面体型水凝胶的制备方法，拟设计合成一系列不同交联度的规整聚乙二醇网络，以其作为模型高分子，借助同步辐射X射线散射技术研究网络高分子在拉伸外场下的结晶行为，建立形变诱导构象熵变化与结晶速率间的定量关系；明确规整网络高分子结晶的临界应变与交联度间关系；阐明链取向与松弛、应力等因素对网络高分子结晶成核、生长和形貌的影响；揭示外场诱导高分子结晶的机理。研究结果可为高分子材料的加工和自增强材料的制备提供理论指导。

高分子材料在熔融加工和服役过程中均受到外场作用，研究外场作用下高分子材料的结构形成和演变对于调控加工工艺和产品性能具有重要意义。本报告以规整聚乙二醇（PEG）网络和辐照交联的反式-1，4-聚异戊二烯（TPI）为研究对象，利用同步辐射X-射线散射技术研究高分子网络的拉伸诱导结晶行为。建立形变诱导构象熵变化与拉伸倍率间的定量关系；阐明TPI中应力诱导晶型转变的机理。主要开展了以下几方面的工作。（1）借鉴类四面体型PEG水凝胶的制备过程，增加透析和干燥步骤，成功制备了不同交联度的PEG网络薄膜。所制备的PEG网络可结晶，其结晶方式为异相成核三维生长，结晶温度、熔点和结晶速率随交联密度增加而降低。（2）以PEG网络为研究对象，通过实验定量验证了应变诱导结晶的热力学理论，并计算了由形变引起的熔体构象熵变化（∆Sdef），∆Sdef为负值，其绝对值随拉伸倍率和交联密度的增加而增大。（3）利用γ-射线辐照成功制备了不同交联度的以α晶为主要晶型的TPI（α−TPI）薄膜，发现α-TPI中的应力诱导α→β晶型转变不受辐照交联程度的影响，说明此晶型转变遵循固-固相转变机理。