It is stressed that the structure plays a decisive role on the property of materials. Materials generally with rigid molecular chains possess outstanding mechanical performances. However, this structure-property relationship is ambiguous in some polyimide (PI) materials. In this study, three typical homo-PI fibers, derived from pyromellitic dianhydride(PMDA)/p-phenylene diamine(PDA), PMDA/4,4′-oxidianiline (ODA) and 3,3′,4,4′-biphenyldianhydride (BPDA)/PDA respectively, were prepared by a two-step wet-spinning method. The tensile strength and modulus of the BPDA/PDA PI fiber were higher than that of the PMDA/ODA PI fiber, while the PMDA/PDA PI fiber was too brittle to take the tensile test. Nevertheless, the rheology and dynamic thermomechanical analysis(DMA) results indicated that the rigidity order of polymer chain was PMDA/PDA > PMDA/ODA > BPDA/PDA. Accordingly, the chain conformations of different PI fibers were described by molecular simulation, and a molecular packing model was proposed to explain this structure-property contradiction.

需要强调的是，结构对材料的性能起着决定性的作用。通常具有刚性分子链的材料具有出色的机械性能。但是，在某些聚酰亚胺（PI）材料中，这种结构-属性关系不明确。在这项研究中，三种典型的均聚PI纤维分别来自均苯四甲酸二酐（PMDA）/对苯二胺（PDA），PMDA / 4,4'-二苯胺（ODA）和3,3'，4,4'-联苯二酐（BPDA）/ PDA分别通过两步湿纺法制备。BPDA / PDA PI纤维的拉伸强度和模量高于PMDA / ODA PI纤维，而PMDA / PDA PI纤维太脆，无法进行拉伸测试。然而，流变学和动态热力学分析（DMA）结果表明，聚合物链的刚性顺序为PMDA / PDA> PMDA / ODA> BPDA / PDA。因此，通过分子模拟描述了不同PI纤维的链构象，并提出了分子堆积模型来解释这种结构-性能矛盾。