Stoichiometry and molecular dynamics of anhydride-cured epoxy resin incorporating octa-glycidyl POSS Co-Monomer

The influence of octa-glycidyl (OG) cubic silsesquioxane and reaction stoichiometry (stoichiometry factor, SF) on the cure chemistry and molecular dynamics of an anhydride-cured epoxy resin is reported. Fourier transform infrared spectroscopy revealed that an excess of epoxide groups suppresses esterification, as does the substitution of the epoxy pre-polymer with OG. Suppressed glass transition temperature (Tg) is reported for any given SF on addition of OG; these results are supported by the dielectric α relaxation behaviour. System-to-system network variations arising from changes in the degree of esterification and etherification are not sufficient to form discrete dielectric β processes. Finally, we propose a generic interpretation for the γ dielectric relaxation involving both competing origins reported in the literature, namely γ1 (local motions of main-chain segments) and γ2 (unreacted moieties). These attributions explain the observed dielectric features and relate these to the chemical composition of each system.