Initial evaluation of novel polyamide-imides and their copolymers as adhesives

Abstract

Abstract�An adhesive screening study was performed at NASA Langley Research Center on two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either of two amide diamines, 3,3'-or 4,4'-diaminobenzanilide (DABA), and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). The two copolymers studied were prepared with a combination of 3,3'-DABP and amide diamines. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness.Lap shear strength (LSS) tests, conducted at room temperature, 177, 204 and 232°C, were the primary criterion for evaluation of the polymers as adhesives. Included in the study were measurements of the glass transition temperature made on fractured specimens for each bonding condition and a visual determination of the type of bond failure for specimens at each test temperature.Of the four adhesive candidates investigated, the best LSS values were obtained with the PAI copolymer identified as LARC-TPI(25% 3,3'-DABA). However, the LSS values were higher for the LARC-TPI polyimide with which the adhesive strengths were compared. The combination of a high molecular weight and the increased interchain electronic interaction associated with the amide group appears to contribute to the poor flow properties observed.