Preliminary evaluation of a poly(phenylquinoxaline) as thermally resistant wire insulation

As part of a program to identify applications for poly(phenylquinoxalines) (PPQs), their evaluation as thermally resistant wire coatings was undertaken. Because of their superior toughness, thermal stability and hydrolytic stability, PPQs appear to offer major advantages over state-of-the-art polyimide-based high temperature wire insulation. These factors in conjunction with a density 15% lower than that of polyimide suggested that aerospace wire insulation, which places a premium on weight reduction, might be an attractive application. Extrusion coating as a method of application was quickly ruled out because of the high glass temperature of the PPQs. Solution coating from m-cresol appeared promising and was evaluated. In this case however, the multistrand nature of aerospace wire led to problems. Air and/or solvent was retained in the interstitial volume between the wire strands, resulting in bubbles and voids in the coating after solvent bake-out. Application to single strand or magnet wire was more successful in that void-free coatings could be obtained.<>