IM7/LARC-IA polyimide composites

• Published in: High performance polymers 1995-03, Vol.7 (1), p.105-124
• Main Authors: Hou, T H, Johnston, N J, St Clair, T L
• Format: Article
• Language: English
• ISSN: 0954-0083
• DOI: 10.1088/0954-0083/7/1/009

LARC-IA (Langley Research Center-Improved Adhesive) aromatic polyimide, based on oxydiphthalic anhydride and 3,4'-oxydianiline, was evaluated as a matrix for high-performance composites. Six poly(amide acid) solutions in N-methylpyrrolidone (NMP), endcapped with phthalic anhydride to various theoretical molecular weights, were synthesized, and their molecular weights and molecular weight distributions determined. High concentrations of low-molecular-weight species were found in all the offset compositions. Except for the 1-percent offset polymer, all fully imidized films failed a solvent-resistance test which involved immersion in acetone, methyl ethyl ketone, toluene, dimethylacetamide, and chloroform for 1 min followed by a fingernail crease. A unidirectional prepreg was fabricated from each of the six resins by both standard drum winding procedures and the LARC multipurpose prepreg machine. An optimal end-capped resin composition was identified (4 percent stoichiometric imbalance) by using, as a screening tool, initial composite mechanical properties at room temperature, 93, 150, and 177 C. Composite engineering properties for the 4 percent offset composition were obtained, including longitudinal tension, transverse flexural, longitudinal compression, interlaminar shear, short block compression, open hole compression, and compression strength after impact. Notably, the CAI strength was 303.2 MPa, showing that the LARC-IA composites have good damage tolerance. (Author)