A high pressure photon correlation study of bulk poly(methylacrylate). Comparison with relaxation processes in poly(ethylacrylate) and related polymethacrylates

Abstract

We report results of the photon correlation polarized light scattering study on the dynamics of bulk polymethylacrylate (PMA) in the temperature range of 7–76 °C and in the pressure range 1–2100 bar. A single relaxation process with a distribution of relaxation times represents the experimental photon correlation functions. The temperature and pressure dependence of the mean relaxation time are analyzed in terms of the VFT and WLF equations. The parameters obtained are discussed in terms of the rotational isomerization model and the free volume model. The results obtained in light scattering agree well with dielectric and mechanical relaxation data. In the case of polyethylmethacrylate (PEMA) and polybutylmethacrylate (PBMA), two overlapping relaxation modes are found. The values of the activation parameters and the relaxation time at the glass transition temperature (Tg) thus obtained characterizing the dynamics of a polymer melt above Tg are compared for PMA, PEA, PEMA, and PBMA.