环氧树脂vitrimer动态结构及可重复加工性能微观机理的固体NMR研究

Vitrimer is a kind of cross-linked polymer with dynamic bonds, which can be reprocessed without destroying the topological network structures. Hence, it combines the properties of thermoplastic and thermoset polymer materials, and has received considerable attention in recent years. However, there are rare studies on dynamic structures and the mechanism of reprocessing ability of vitrimers. Herein, this project is aimed to systematically investigate the microscopic origin of the dynamic structures and the reprocessing ability of epoxy resin vitrimers. Multiple solid-state NMR methods, in combination with DSC and DMA, will be utilized to investigate the hierarchical structures and dynamics of epoxy vitrimers, and thus to elucidate the effect of chain structures and dynamics on the macroscopic mechanical properties and reprocessing abilities as well as the corresponding physical meaning of the vitrification temperature (Tv) in epoxy vitrimers. On that basis, we would like to further develop novel solid-state NMR methods for in-situ detecting the transesterification exchange reaction in the epoxy vitrimers, in order to further elucidate the structure-property relationship and the mechanism of reprocessing ability at a molecular level, and thus to provide experimental and theoretical guidance for designing high-performance vitrimer materials. To a large degree, this project could well bridge the gap between polymer physics, polymer chemistry and polymer engineering at a molecular level.

Vitrimer通常是指含动态键的交联聚合物，且在不破坏交联网络拓扑结构的情况下具有可重复加工性能，因此兼具了热固性和热塑性高分子材料的优点，在近年来被广泛关注，然而对vitrimer材料动态结构及可重复加工性能微观机理的研究却鲜有报道。因此本项目旨在制备环氧树脂 vitrimer材料的基础上，利用多种固体NMR技术结合DSC，DMA等方法，研究环氧树脂vitrimer材料的微观链结构和动力学对vitrimer宏观力学性能及可重复加工性能的调控规律，以及vitrimer转变温度Tv所对应的物理意义及微观机理，并进一步发展原位检测环氧vitrimer体系中动态酯交换的固体NMR新方法，进而从分子水平上阐明环氧树脂vitrimer材料的结构—性能关系，为设计高性能高分子材料提供实验和理论指导，并从分子层面建立高分子物理—高分子化学—高分子加工之间的联系。

本项目研究了以葵二酸(sebacic acid, SA) 和双酚A二缩水甘油醚(diglycidyl ether of bisphenol A, DEGBA)作为原料制备的环氧树脂vitrimer材料。研究表明，当用醋酸锌(Zn(OAc)2)作为催化剂时，Zn2+离子往往容易聚集，在样品中的分布存在着极大的不均匀性。然而，当用1,5,7-三氮杂双环［4.4.0］癸-5-烯(Triazabicyclodecene, TBD)作为催化剂时，虽然TBD催化效率高，但是TBD会参与环氧树脂的反应并成为环氧树脂网络的一部分，从而极大地影响环氧树脂的宏观力学性能。固体质子多量子实验清楚地揭示了环氧树脂的交联密度随TBD含量增加而降低，同时TBD含量越大，交联网络结构不均匀性越大，网络缺陷的含量随着TBD含量的增加而升高。进一步，为了避免Zn2+离子的聚集问题，我们制备了含Zn2+离子的大分子催化剂聚(丙烯腈-co-甲基丙烯酸锌) (Zn-PAM, poly(acrylonitrile-co-zinc methacrylate))用于催化环氧树脂的酯交换反应，不仅具有较高的催化效率，同时大分子的加入也极大地提高了环氧树脂的杨氏模量。最外，基于对vitrimer材料的认识，我们也制备了多种含动态键的高性能聚合物材料，包括具有多重刺激响应性的聚氨酯材料，含双重动态键的聚丙烯酸正丁酯(PBA)弹性体等，同时发展和应用最新的固体NMR深入揭示了材料的结构和动力学演化规律。