A series of copolyimide (co-PI) fibers containing trifluoromethyl units were successfully obtained on the molecular design of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, p-phenylenediamine, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP) via a widely utilized two-step wet-spinning method. Significant variations on the microstructures and properties of the resulting co-PI fibers were observed after the incorporation of HFBAPP moieties. The tensile strength and initial modulus of the fibers decreased from 0.70 GPa to 0.38 GPa and from 69.63 GPa to 9.60 GPa, respectively. However, the dielectric permittivity decreased from 3.62 to 2.85 in the frequency of 10 MHz as a result of the incorporation of trifluoromethyl units. Two-dimensional wide-angle X-ray diffraction showed that the fibers exhibited highly oriented molecular alignments along the fiber direction and low lateral packing degree in the transverse direction. In addition, the co-PI fibers possessed excellent thermal–oxidative stabilities with the 5% weight loss temperature ranging from 532°C to 552°C under nitrogen atmosphere and the glass transition temperature ranging from 312°C to 330°C.

中文翻译：

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含三氟甲基单元的聚酰亚胺纤维的微观结构演变及性能

基于3,3',4,4'-联苯四甲酸二酐、对苯二胺和2,2-双[4-(4-氨基苯氧基）苯基]六氟丙烷（HFBAPP）通过广泛使用的两步湿纺方法。在掺入 HFBAPP 部分后，观察到所得 co-PI 纤维的微观结构和性能发生显着变化。纤维的拉伸强度和初始模量分别从 0.70 GPa 下降到 0.38 GPa 和从 69.63 GPa 下降到 9.60 GPa。然而，由于引入了三氟甲基单元，介电常数在 10 MHz 频率下从 3.62 下降到 2.85。二维广角 X 射线衍射表明，纤维在纤维方向上表现出高度取向的分子排列，在横向上表现出较低的横向堆积度。此外，co-PI纤维具有优异的热氧化稳定性，氮气氛下5%的失重温度范围为532°C至552°C，玻璃化转变温度范围为312°C至330°C。