Dehydration-induced structural relaxation effects in poly(methyl methacrylate)

The Thermally Stimulated Depolarization (TSD) dielectric technique and Diel ectric Relaxation Spectroscopy (DRS) have been used in order to investigate aging phenomena in poly(methyl methacrylate) (PMMA). Earlier TSD studies o n amorphous PMMA report peculiar dielectric relaxation signals within the r ange of the glass transition (at similar to 378 K) and the secondary relaxa tion (similar to 230 K). In the present study, an intense TSD current relax ation band maximizing around 310 K is tentatively attributed to the molecul ar mobility due to a residual free volume below the glass transition temper ature, T-g, that allows structural recovery at the free volume released fro m the desorption of H2O molecules during evacuation. Limited motions in the main backbone provoke dipole (re)orientation of the ester carbonyl pendant groups with an activation energy E=0.85+/-0.05 eV, being responsible for t he latter dielectric relaxation effect. Alternative attributions based on t he short-range jump relaxation of electric charges and boundary effects are also discussed.