Synthesis of epoxy and phenyl groups-containing polyhedral oligomeric silsesquioxane of large Si₁₆O₂₄ cage and its flame retardant and mechanical performances on epoxy resins

A kind of the epoxy and phenyl groups-containing POSS of the regular cage of 16 silicon atoms (EPHPOSS) was synthesized successfully via the hydrolysis-condensation reaction of phenyltrimethoxysilane and 2-(3,4-glycidoxypropyl) propyltrimethoxysilane, and its chemical structure was characterized. To improve the comprehensive performances of the epoxy resin (EP), EPHPOSS in different ratios was incorporated into the EP by thermal curing technology. It is obtained that the EPHPOSS has a homogeneous dispersion in the EP composites and plays an important role in enhancing the bending strength and thermal properties of the EP composites. The EP composite with 10 wt% EPHPOSS has a limiting oxygen index (LOI) value of 27.8%, higher than the LOI of 23.2% of the pure EP. The peak of heat release rate, total heat release, and total smoke release of the EP composites with the EPHPOSS are reduced obviously. In flame retardant mechanism of the EPHPOSS on the EP, the microstructures of the burning char and TG-FTIR of the EP composites were achieved, it is suggested that the EPHPOSS promotes the formation of compact and continuous char layers and reduces the production of the organic combustible gases.