Main dielectric relaxation of poly(methyl acrylate)–polystyrene interpenetrating polymer networks

Two series of poly(methyl acrylate)–polystyrene sequential interpenetrating polymer networks were prepared by free radical polymerization using ethyleneglycol dimethacrylate as cross-linking agent. In one of them the cross-linking density was very low and the IPNs presented phase separation. The main dielectric relaxation appears in the IPNs in the same position in the frequency axis and almost with the same shape as in the pure PMA network. Nevertheless the ratio of the relaxation strength to the weight fraction of PMA in the IPN decreases slightly with the increase of polystyrene content. The other series of IPNs were highly cross-linked, in these IPNs a dielectric relaxation still appears almost at the same temperature as in pure PMA network but it changes in its shape and an important decrease of the normalized relaxation strength is shown. The main relaxation ascribed to a polystyrene rich phase can also be observed due to the polarity of the cross-linking agent and a significant shift of this process towards low temperatures as the content of PMA in the IPN increases is observed. This feature was confirmed using dynamic-mechanical measurements.