Preparation and mechanism of toughening and flame retardance of epoxy resin using novel silsesquioxane molecules

To simultaneously improve epoxy resin's toughness and flame retardancy, novel polyhedral oligomeric silsesquioxane with two functional epoxy and methacryloxy groups (EM-POSSs) were synthesized. Various analytical methods showed that caged POSS compounds with T8, T10, and T12 structures were successfully synthesized. The epoxy groups improved the dispersibility of POSS in the epoxy resin matrix and participated in the curing reaction to enhance the mechanical properties and thermal stability. Furthermore, the methacryloyloxy groups polymerized at high temperatures to form longer and more flexible chain groups, thereby improving the toughness of the epoxy networks. It was found that EM-POSSs significantly improved epoxy the resin's toughness and flame retardancy. Compared with pure epoxy resin, the peak heat release rate (PHRR) of epoxy composites was reduced by 45%, while the bending strength, tensile strength, and impact toughness increased by 55%, 50%, and 57.1%, respectively.