A series of high-performance polyimide copolymer (co-PI) fibers containing phenylenebenzoxazole moiety with one hydroxyl group are synthesized based on the copolymerization of 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) with two diamine monomers, namely, p-phenylenediamine (p-PDA) and 5-anino-2-(2-hydroxy-4-aminobenzene)-benzoxazole (p-mHBOA), through a two-step method. The molar ratio of p-PDA/p-mHBOA varies from 10/0 to 0/10. Influences of the p-mHBOA moieties on the thermal stability, crystal structure, crystal orientation, microvoid morphology, and mechanical properties are systemically investigated. Fourier transform infrared results confirm that intra/inter molecular hydrogen bonds come from the OH group and nitrogen atom of the benzoxazole group and/or OH group and the oxygen atom of the carbonyl group of cyclic imide. The glass transition temperatures (T_gs) of co-PI fibers are in the range of 290 °C–325 °C. The prepared fibers show excellent thermal stabilities, and their T_5% is within 528 °C–542 °C in air. Two-dimensional wide-angle X-ray diffraction spectra indicate that homo-PI and co-PI fibers present a regularly arranged polymer chains along the fiber axial direction. Moreover, the ordered molecular packing along the transversal direction of fibers is destroyed by the copolymerization. Small-angle X-ray scattering results show that co-PI fibers with optimal mechanical properties exhibit the shortest average length (L) and the smallest radius ($\overline{R}$) of microvoids. When the p-mHBOA/p-PDA molar ratio is 5/5, the fracture strength and initial modulus can reach approximately 30.31 cN/dtex (4.40 GPa) and 894.88 cN/dtex (129.8 GPa), respectively. The relationship between structure and mechanical properties is also discussed.

基于3,3'，4,4'-联苯四甲酸二酐（BPDA）与两种二胺单体的共聚反应，合成了一系列含有带有一个羟基的亚苯基苯并恶唑基团的高性能聚酰亚胺共聚物（co-PI）纤维。 ，p苯二胺（p -PDA）和5- ANINO-2-（2-羟基-4-氨基苯） -苯并唑（p -mHBOA）中，通过两步法。的摩尔比p -PDA / p -mHBOA变化从10/0到0/10。p的影响系统研究了-mHBOA部分的热稳定性，晶体结构，晶体取向，微孔形态和机械性能。傅里叶变换红外结果证实分子内/分子间氢键来自苯并恶唑基和/或OH基的OH基和氮原子以及环状酰亚胺的羰基的氧原子。co-PI纤维的玻璃化转变温度（T _g s）在290°C至325°C之间。制备的纤维表现出优异的热稳定性，其T值为_5％空气中温度在528°C–542°C之内。二维广角X射线衍射光谱表明，均聚PI和共聚PI纤维沿纤维轴向呈规则排列的聚合物链。而且，沿着纤维的横向方向的有序分子堆积被共聚破坏。小角度X射线散射结果表明，具有最佳机械性能的co-PI纤维表现出最短的平均长度（L）和最小的半径（L）。$\overline{\mathrm{[R}}$）的微孔。当p -mHBOA / p -PDA摩尔比为5/5，断裂强度和初始模量可以达到约30.31厘牛顿/分特（4.40 GPa）的和894.88 CN /分特（129.8 GPa）的，分别。还讨论了结构和机械性能之间的关系。