Dielectric study of low glass transition temperature cycloaliphatic UV-curable epoxy networks

This work focuses on the dielectric properties of a UV-cured epoxy network with a low glass transition temperature obtained through photoinduced copolymerization of a cycloaliphatic diepoxy monomer, 3,4-epoxycyclohexylmethyl-3´,4´-epoxycyclohexanecarboxylate (CE), with 1,6-hexanediol diglycidyl ether (HDGE). The crosslinking density of the system has been tuned using different amounts of the low glass transition temperature HDGE comonomer (up to 60 wt.% HDGE). The structural morphology and space charge obtained with the Thermal Step Method were studied following various thermal treatments of the samples. Both the thermal properties and the dielectric responses (dielectric constant) for the UV-cured HDGE/CE systems turned out to be dependent on the structural morphology and composition of the polymer network. In particular, two relaxation modes, γ, β and α were observed, attributed to local molecular motions. Lastly, the potential effect of moisture and/or ions and the effect of space charge on the copolymers were also investigated.