Influence of phenyl-trisilanol polyhedral silsesquioxane on properties of epoxy network glasses

The influence of phenyl-trisilanol polyhedral silsesquioxane (POSS-triol) on the thermo-mechanical properties and curing of epoxy-amine networks were investigated using dynamic mechanical analysis (DMA) and Fourier transform infrared spectroscopy (FT-IR). Two of the most common epoxy monomers, diglycidyl ether of Bisphenol A (DGEBA), tetraglycidyl diamino diphenyl methane (TGDDM) were used. These epoxies were cured with linear aliphatic diamine: 2-Methyl-1,5-pentadiamine (Dytek®A) or diamine terminated polypropylene oxide (Jeffamine® D230). Using an identical curing schedule, when minor amounts of POSS-triol were added to the epoxy-amine networks, we found a significant improvement on value of Tg. Due to the small quantity of POSS-triol used, this enhancement in Tg is attributed to the catalytic activity of phenyl-trisilanol POSS in promoting a more completely cured epoxy network. This argument is consistent with observed increases in the rubbery plateau modulus due to increases in the crosslink density. But unlike other catalysts such as phenol, we did not observe acceleration of reaction in the pre-gelation stage by this acidic POSS-silanol. Because of its nanoscopic size, this acidic POSS-silanol promotes additional epoxy-amine crosslinking in the post-vitrification stage, which is dominated by diffusion-control mechanisms. We believe this can be utilized in fabrication of fiber-reinforced composites using the resin transfer molding process, where maintaining the low viscosity for a period of time is required to eliminate porosity and to produce higher Tg materials at a lower post-cure temperature.