Development of High-Performance Composites with Molecular Weight Controlled Polyimide Oligomers End-Capped with Phenylethynyl Groups

A series of molecular weight controlled polyimide oligomer (Oligo-PI) resins were developed via the polymerization of 4,4′-(1,3-phenylenedioxy)dianiline (TPE-R), 2,3′,3,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4-phenylethynyl phthalic anhydride (PEPA). PEPA was served as the molecular weight controlling and reactive end-capping agent. Oligo-PI resins have an asymmetric and amorphous structure, which could make better processability to fabricate composites. To investigate the effect of molecular weight (MW) and chain extension structures of phenylethynyl groups by thermal curing on thermal and mechanical properties, carbon fabric reinforced Oligo-PIs (Oligo-PI/CFs) were prepared via hot press technique. Morphology, mechanical and thermal properties of Oligo-PI/CFs were measured by SEM, TGA, IZOD impact tester, and UTM (three-point bending test). As MW got higher and the ordered network structures were formed, the composite exhibited excellent thermal stability. Flexural strengths also increased by building the crosslinked structures. On the other hand, impact strengths were less influenced. Among Oligo-PI/CFs, Oligo-PI/CF-3 showed comparatively good performance. The mechanical properties of Oligo-PI/CF-3 (5 ply) was evaluated at both 25 °C and 200 °C. The composite maintained high strengths even at high temperatures, demonstrating the durability of Oligo-PI/CFs in harsh conditions utilized for the aerospace and military applications.