Relaxation Spectroscopy of the Mechanical β-Relaxation in Poly(n-alkyl methacrylate)s in Glassy State by Stress Relaxation Measurements

Abstract

The validity of the time-temperature reducibility and the similarity between the mechanical and dielectric relaxations were examined in the case of the β-relaxation due to motion of the side chains in polymethyl, polyethyl and poly-n-propyl methacrylates by stress relaxation measurements. The shear relaxation modules was measured from 5 sec to 900 sec in the temperature range fromca. -110°C toca. 30°C. Using these data, it is shown that the time-temperature reducibility is valid for the β-relaxation in the glassy state below a certain critical temperature, and that activation energy and shape of the relaxation spectrum are independent of side-chain length while relaxation strength is proportional to the number of side chains in unit volume as in the case of the dielectric β-relaxation. The applicability of the two-site model is also examined.