Organic/inorganic hybrid materials based on silsesquioxanes derived from (3-methacryloxypropyl) trimethoxysilane and their blends with vinylester resins

The crosslinking of blends of a silsesquioxane (SSO) derived from (3-methacryloxypropyl) trimethoxysilane, variable amounts of a vinylester resin (VE, dimethacrylate of bisphenol A), and benzoyl peroxide (BPO) or dicumyl peroxide (DCP) as initiators, was followed by differential scanning calorimetry (DSC). For the neat SSO a thermally-initiated polymerization was observed in the 150–250°C range, leading to a conversion close to 22% of the initial C=C groups. The final conversion could be increased to a maximum value close to 83%, by adding an initiator and using a thermal cycle attaining temperatures in the range of 200°C. The use of variable amounts of VE as a co-monomer produced a slight increase of the final conversion in SSO/VE/BPO blends. Neither the conversion of double-bonds nor the addition of the VE had any effect on the onset temperature of thermal degradation, which was associated to the presence of the methacryloxypropyl groups supplied by the SSO and the VE resin. However, a distinct two-step degradation process was observed in the presence of VE. Coatings based on SSO/VE/BPO blends exhibited more uniform thicknesses and lower values of the microhardness than those devoid of VE. However, the conversion of C=C groups did not show any significant effect on the values of microhardness.