Study of the dielectric relaxation of poly(phenylpropyl acrylate) and poly(phenylpropyl methacrylate): Effect of slight differences in chemical structure

The effect of slight differences in the chemical structure of two structurally related polymers, namely poly(phenylpropyl acrylate) (P3Ph1PA) and poly(phenylpropyl methacrylate) (P3Ph1PM), on the molecular mobility was studied by means of differential scanning calorimetry and dielectric relaxation spectroscopy. A comparative study of the dielectric relaxational behaviour of two structurally close polymers, containing aromatic side groups, was carried out in order to analyse how slight differences in the chemical structure affect the molecular responses to perturbation field. Specifically, poly(phenylpropyl acrylate) (P3Ph1PA) and poly(phenylpropyl methacrylate) (P3Ph1PM) were studied using differential scanning calorimetry and dielectric relaxation spectroscopy in the frequency range 10^-2-10⁶ Hz and temperature window of -80 to 120 °C. Both techniques show one glass-rubber transition for P3Ph1PA and two for P3Ph1PM, which evidence the great effect of the methyl groups on the segmental motions of the polymer. Phenomenological analysis of the data was carried out in order to establish the strength, width and fragility parameters of the glass-rubber transitions. In the case of P3Ph1PA, the strength is found to be larger than for P3Ph1PM, pointing out that the methyl group disturbs the mobility. Conductive processes dominate the dielectric spectra at high temperatures and low frequencies.