Dielectric and ultrasonic studies of the δ‐relaxation of poly(ethyl methacrylate)

Abstract

AbstractComplex dielectric constants at frequencies of 110 Hz, 1 kHz, and 10 kHz and complex elastic moduli at 34 kHz and 3 MHz were measured in the temperature region the of δ relaxation of poly(ethyl methacrylate) (PEMA) down to 4°K. The temperatures of the loss maximum correlate well with literature values of the temperatures of mechanical loss maxima and with T1 minima. The activation energy is 2.1 kcal/mole. The energy map for the internal rotation of the ester ethyl group of PEMA was calculated; the activation energy and the energy difference between the two energy minima (0.31 kcal/mole) were found to agree well with those determined from experiment. The strength of dielectric relaxation is interpreted on the basis of 0.11 D as the dipole moment of the ethyl group. The strength of mechanical relaxation obtained in the present study as well as the previously published values are discussed. The volume change arising from the internal rotation of an ethyl group is found to be comparable at low temperatures with the van der Waals volume of the ethyl group and to decrease with increasing temperature.