PROCESSING AND PROPERTIES OF IM7 LARC(TM)-IAX2 POLYIMIDE COMPOSITES

LARCTM-IAX2 (Langley Research Center-Improved Adhesive eXperimental re sin 2) aromatic polyimide, based on oxydiphthalic anhydride (ODPA), be nzophenone tetracarboxylic acid dianhydride (BTDA), and 3,4-oxydianili ne (3,4'-ODA), was evaluated as a matrix for high performance composit es. This polymer is a modified version of the baseline LARCTM-IA polyi mide 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 resi stance in acetone, methylethylketone, toluene, DMAc, and chloroform co mpared to the baseline LARCTM-IA film. Unidirectional prepregs were fa bricated from both solutions using the Langley multi-purpose prepreg m achine. 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 b ut required more severe processing conditions than those for the basel ine material. Short beam shear strength and longitudinal flexural prop erties 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 p roperties such as fracture toughness, unnotched tensile strength, notc hed and unnotched compressive strengths and moduli, compression streng th after impact and open hole compression strength were also measured. The enhanced solvent resistance, more difficult processability, and h igher flexural moduli compared to those for the baseline composites we re attributed to an increase in polymer backbone stiffness due to the presence of BTDA. No differences in the physical and mechanical proper ties were observed between composites made in NMP and DMAc. The result s have helped define a chemical approach for improving solvent resista nce in thermoplastic polyimide materials.