Zirconium-methacrylate oxoclusters as new hybrid materials for the modification of epoxy systems

Oxozirconium clusters bearing methacrylate moiety (ZrMe) were synthesized by sol–gel process and used in epoxy networks to develop epoxy-based nanocomposites with potential application as encapsulant for light-emitting diode. Diglycidyl ether of bisphenol A-based epoxy resin was previously functionalized with acrylic acid to introduce some vinyl groups in the matrix and improve its interaction with the oxocluster. The ZrMe particles were previously dispersed in the epoxy matrix or in the 4-methyl-tetrahydrophthalic anhydride used as hardener, and the systems were cured with anhydride or with a combination of anhydride and benzoyl peroxide. The last compound promotes the covalent bond between the epoxy matrix and the ZrMe through free radical reactions between the vinyl groups. The dispersion of ZrMe into the epoxy matrix resulted in a significant increase in viscosity, mainly for systems dispersed with a combination of high shear mechanical mixing and ultrasonification. The dispersion of ZrMe into the anhydride resulted in nanocomposites with higher transparency, better dispersion of the oxocluster into the matrix bulk, as observed by transmission electron microscopy, and higher thermal conductivity, mainly for systems cured with anhydride and peroxide. The use of anhydride in combination with BPO also resulted in significant increase in glass transition temperature.