Hybrid Structured Phenylethynyl Silsesquioxane Resin Composites

Thermosetting polyimides terminated with phenylethynly phthalic imides are the current state-of-the-art high temperature resin for use in structural composite applications. However, due to the presence of imide group these resins often suffer high moisture uptake leading to property degradation during use. In addition, the need to remove condensation near the crosslinking reaction temperature as well as high glass transition temperature of unreacted oligomers, the processing window for this class of thermosetting is very narrow. Hence, the need to develop compounds with the same terminating group with ease of processing is of significant interest. In this work, double-decker shaped silsesquioxane (DDSQ) terminated with multiple phenylethynyl groups was developed and curing process investigated. It was anticipated that DDSQ as the backbone can provide the needed monodispersed characteristics in its molecular weight, while phenylethynyl groups form different isomers (region- and stereo-) about the SiO core of DDSQ. This approach provides ease of processing while eliminate crystallinity. In addition, the inorganic nature of these compounds also exhibited a significant reduction in the moisture uptake which can greatly enhance in-service performance of composites. Synthesis and purification of needed chlorosilanes and the subsequence separation of these functionalized DDSQs by liquid chromatography were performed without the need to use fractional crystallization as the first preparation step are presented. This approach greatly reduces the complexity and enables continuous process.