Hou, TH; Chang, AC; Johnston, NJ; Stclair, TL
LARCTM-IAX2 (Langley Research Center-Improved Adhesive eXperimental resin 2) aromatic polyimide, based on oxydiphthalic anhydride (ODPA), benzophenone tetracarboxylic acid dianhydride (BTDA), and 3,4-oxydianiline (3,4'-ODA), was evaluated as a matrix for high performance composites. This polymer is a modified version of the baseline LARCTM-IA polyimide made from ODPA and 3,4'-ODA. Two poly (amide acid) solutions end-capped with phthalic anhydride were synthesized in N-methypyrrolidone and N,N-dimethylacetamide (DMAc) with ODPA to BTDA ratios of 4:1 and 3:1, respectively. Fully imidized films exhibited improved solvent resistance in acetone, methylethylketone, toluene, DMAc, and chloroform compared to the baseline LARCTM-IA film. Unidirectional prepregs were fabricated from both solutions using the Langley multi-purpose prepreg machine. A separate molding cycle (350 degrees C/250psi) was developed for each prepreg based upon solvent-volatile depletion characteristics. These cycles consistently yielded void-free consolidated laminates but required more severe processing conditions than those for the baseline material. Short beam shear strength and longitudinal flexural properties were measured at room temperature. 93 degrees, 150 degrees, and 177 degrees C. Notably, the flexural moduli were about 5% higher than those reported for the baseline composite. In addition, engineering properties such as fracture toughness, unnotched tensile strength, notched and unnotched compressive strengths and moduli, compression strength after impact and open hole compression strength were also measured.The enhanced solvent resistance, more difficult processability, and higher flexural moduli compared to those for the baseline composites were attributed to an increase in polymer backbone stiffness due to the presence of BTDA. No differences in the physical and mechanical properties were observed between composites made in NMP and DMAc. The results have helped define a chemical approach for improving solvent resistance in thermoplastic polyimide materials.