Visible-light photopolymerization of DGEBA promoted by silsesquioxanes functionalized with cycloaliphatic epoxy groups

Abstract

Diglycidyl ether of bisphenol A (DGEBA) is among the most popular and widely used epoxy monomers. This monomer is commonly used in thermal network polymerizations with amines, phenols, isocyanates or mercaptans as curing agents. However, the photoinitiated polymerization of DGEBA is very sluggish and hence finds little use in high-speed photocuring applications. In this contribution, we demonstrated that this monomer can undergo very fast visible-light photopolymerization when combined with a silsesquioxane (SSO) functionalized with reactive epoxycyclohexane groups. The SSO was synthesized via alkoxysilane hydrolysis/condensation chemistry, using DGEBA as a solvent. We found that the photopolymerization of DGEBA is markedly accelerated as the amount of SSO in the mixture is increased. The promoter effect on the reactivity of DGEBA was ascribed to a combination of both thermal and copolymerization effects. Using dynamic mechanical analysis, we demonstrated that the resulting hybrid materials present a single-phase network structure, where the SSO species function as highly multifunctional epoxy reactants.