Relaxation Dynamics of Poly(methyl acrylate) at Elevated Pressure

Dielectric relaxation and complex heat capacity were carried out on high molecular weight poly(methyl acrylate) (PMA). The temperature was found to exert a stronger effect than density on the segmental dynamics, as reflected in the magnitudes of the scaling exponent, 2.55, and the ratio of isochoric and isobaric activation energies, 0.67. The dispersion of the heat capacity and dielectric loss were used to obtain estimates of the number of dynamically correlated segments. In accord with prior results on molecular liquids and from simulations, the extent of the dynamic correlations in PMA depends only on the relaxation time. This behavior differs from that of the fragility, which decreases with pressure, showing the disconnect between dynamic heterogeneity and fragility.