Correlating structural and electrical properties in radiation-cured polymers

Radiation-cured epoxy and acrylate-based materials are used in a number of applications where curing under ionizing radiations is preferred to the classical thermal curing process. Because mechanical properties are often the key features in these applications much less attention has been paid to their electrical properties. We report on the dielectric properties of two classes of radiation-cured materials being typical of two classes of polymerization: free radical mechanism (acrylate-based formulation) and cationic mechanism (epoxy-based formulation). Questions arise as regards the electrical properties due to the complex formulation aiming at controlling the network properties (mechanical properties, degree of cure, glass transition temperature) and to the need of initiators in cationic polymerization with the inclusion of pair of ions in the network. Samples are 1mm-thick plaques, being cured under electron-beam. Different formulations are tested with the aim to investigate the influence of the network structure on electrical properties with specific emphasis on the nature of initiator (iodonium or sulfonium salts with various counter ions) and its concentration in epoxy-based formulation and reactive diluents in acrylate-based formulation. Structural and thermo-mechanical characterization is correlated with the electrical properties being current-voltage characteristics, space charge distribution and dielectric spectroscopy. Mechanisms driving the observed properties are presented and discussed.