Dynamic light scattering from bulk poly(n‐hexylmethacrylate) near and above the glass transition

Photon correlation spectra of polarized scattered light from poly(n‐hexylmethacrylate) PHMA (Mw = 1.6·105, Tg = −5°C) have been studied in the temperature range of −2–25°C. The experimental time correlation functions over the time range 10−6−102 s were represented by the Kohlrausch‐Williams‐Watts (KWW) function exp{−(t/τ)β} with a virtually temperature‐independent distribution parameter β = 0.27 ± 0.02. The observed relaxation functions were also analyzed in terms of a continuous distribution of retardation times L(τ) by means of a direct inverse Laplace transformation. The computed L(τ) distributions reveal a broad single peak structure in agreement with the results of the single KWW fit. The temperature dependence of τ is very similar to that of the shift factors obtained from measurements of the shear modulus and the stress relaxation modulus in the glass‐rubber region. Conversely, the values of τ compare well with those extracted from the experimental dielectric loss peaks consistently represented in the time domain by the KWW function. These findings suggest that the slow density fluctuations in bulk PHMA are associated with the primary glass‐rubber or α‐relaxation, which, however, displays an unusual low apparent Arrhenius activation energy and a rather low β value. PHMA exhibits significant dynamic light scattering with correlation times faster than 10−6 s near Tg.