Preparaton Of High Perofrnance Polyimide Fibers Based On BPDA-DABA-BIA

As one of the high performance fibers, polyimide fiber can be widely used in nationaldefense construction, spaceflight, medical apparatus, ocean exploitation and microelectronicsfields due to its outstanding mechanical properties, excellent thermal stability, good dielectricproperty and radiation resistance. However, the preparation of polyimide fibers has difficult andhot issues in the field of high performance fibers. In this thesis, a series of novel copolyimidefibers were developed via a two-step spinning technology, including the fiber formation ofpolyamic acid and thermal imidization processes. Moreover, to further improve the properties ofpolyamic acids solution and the spinnability, partial imidization for the spinning solution wasemployed to produce denser polyimide fibers a relative good mechanical property. The maincontents are following:In the present work, a series of novel co-polyamic acids containing aromatic heterocyclewerewere synthesized by copolymerization of3,3’,4,4’-biphenyltetracarboxylic dianhydride (BPDA),2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and4-amino-N-(4-aminophenyl)benzamide(DABA). The composition and structure of polymers were confirmed by FTIR. The polyimidefilms have good transparency in the visible range which are confirmed by UV-vis spectra.Thermogravimetri analysis (TGA) results showed that the5%weight loss temperature of thepolyimides ranges from534℃to545℃, and the10%weight loss temperature ranges from564℃to580℃in nitrogen atmosphere.The polyamic acid fibers were prepared by wet spinning. Various coagulation compositionsand draw ratios in coagulation and water baths were carried out to obtain the optimal spinningparameters. The polyimide fiber can be easily obtained by the thermal imidization of the precursorfiber, and exhibited the excellent the mechanical properties and thermal stability. For instance, Thetensile strength of heat-drawn polyimide fiber with BIA:DABA=7:3was16.0cN/dtex, higher by250%compared to the corresponding as-imidized fibers. As measured by dynamicthermomechanical analysis (DMA), the glass transition temperature (Tg) of fiber was347℃, andthe activation energy was574kJ/mol.To improve the spinnabilty of polymer solutions, a series of polyamic acid (PAA) solutions with various pre-imidization degrees were prepared by adding different amount of dehydratingreagents. The proportion of imide rings in polyamic acid was measured by FTIR and thepre-imidization degrees were consistent with the theoretical values. The whole experimentalbinodal curves of (PAA-PI)-DMAc-H2O were completed by the cloud point titration. Thethermal stability of PAA fibers were analyzed by TGA and DMA. The polyimide fiber exhibitedan enhanced mechanical properties. The tensile strength of polyimide fiber with a pre-imidizationdegree of5%was18.6cN/dtex, which are significantly enhanced by16%, compared with the nonpre-imidized samples.