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A new polymerized monomeric reactant (PMR)-type polyimide, designated TriA X, was investigated to determine polymer structure, processability, thermal, and mechanical properties and establish the relationship between the molecular structure and those properties. TriA X is a PMR-type polyimide with an asymmetric, irregular, and nonplanar backbone. Both the imide oligomers and the cross-linked polyimides of TriA X exhibited loose-packed amorphous structures, independent of thermal processing. The peculiar structures were attributed to the asymmetric backbone, which effectively prevented the formation of closed-packed chain stacking typically observed in polyimides. The imide oligomers exhibited a lower melt viscosity than a control imide oligomer (symmetric and semi-crystalline), indicating a higher chain mobility above the glass transition temperature (Tg). The cured polyimide exhibited a Tg = 362°C and a decomposition temperature = 550°C. The cross-linked TriA X exhibited exceptional toughness and ductility (e.g. 15.1% at 23°C) for a polyimide, which was attributed to the high-molecular-weight oligomer and loose-packed amorphous structure. The thermal and mechanical properties of TriA X surpass those of PMR-15 and AFR-PE-4. [ABSTRACT FROM AUTHOR]

A new type of polyimide, designated TriA X, has been developed for high-temperature composite applications. TriA X is a polymerized monomeric reactant (PMR)-type polyimide derived from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 2-phenyl-4,4′-diaminodiphenyl ether (p-ODA), and phenylethynyl phthalic anhydride (PEPA). The polymer has an asymmetric, nonplanar backbone, resulting in an amorphous structure and high toughness. In this work, a TriA X resin (with degree of polymerization n = 7 in the imide oligomer) was investigated for processability and performance in carbon fiber composites. Rheological measurements were performed on an oligomer with a low degree of imidization to understand the chemo-rheology of the resin system and determine a suitable B-staging temperature. A composite molding cycle was designed, which yielded fully consolidated woven carbon fiber laminates. Void contents in panels produced with this molding cycle were <0.1% as measured by image analysis (IA) of polished sections, and <0.2% as measured by X-ray micro-computed tomography (micro-CT). Matrix-dominated mechanical properties of composites fabricated with the TriA X polymer exceeded those of PMR-15 and AFR-PE-4 composites. These mechanical properties and a measured glass transition temperature of 367°C indicate potential for use of this resin system in high-temperature composites. [ABSTRACT FROM AUTHOR]