Temperature Dependent Impedance Spectroscopy and Thermally Stimulated Depolarization Current (TSDC) Analysis of Disperse Red 1-co-Poly(methyl methacrylate) Copolymers

The dielectric relaxation processes of polymethyl methacrylates that have been functionalized with Disperse Red 1 (DR1) in the side chain (DR1-co-MMA) were studied with temperature dependent impedance spectroscopy and thermally stimulated depolarization current (TSDC) techniques. Copolymers with dipole contents which varied between 10 mol% and 70 mol% were prepared. All samples showed dipole relaxations above the structural-glass transition temperature (T-g). The beta-relaxation of the methyl methacrylate (MMA) repeating unit was most visible in DR1(10%)-co-MMA and rapidly vanishes with higher dipole contents. DSC data reveal an increase of the T-g by 20 degrees C to 125 degrees C with the inclusion of the dipole into the polymethyl methacrylate (PMMA) as side chain. The impedance data of samples with several DR1 concentrations, taken at several temperatures above T-g, have been fitted with the Havriliak-Negami (HN) function. In all cases, the fits reveal a dielectric response that corresponds to power-law dipolar relaxations. TSDC measurements show that the copolymer can be poled, and that the induced polarization can be frozen by lowering the temperature well below the glass transition. Relaxation strengths Delta epsilon estimated by integrating the depolarization current are similar to those obtained from the impedance data, confirming the efficient freezing of the dipoles in the structural-glass state.