Influence of azobenzene concentration on the dielectric behavior of amorphous comb-like copolymers with photochromic side groups

Dielectric spectroscopy in the frequency range from 10−2 to 106 Hz and in the temperature range from 190 to 440 K is employed to study the effect of azobenzene concentration on the dielectric relaxation processes of an amorphous comb-like copolymethacrylate. Four concentrations (x=29, 45.5, 54, and 74.5 mol%) of photochromic group 4-amino-azobenzene were investigated, where as comonomer a methacrylate unit having a derivative of benzanilide in the side group is used. Two prominent processes, the β-relaxation at low temperatures which is related to rotational fluctuations of the mesogenic unit around its long axes and the dynamic glass transition (α-relaxation, segmental dynamics) at higher temperatures are observed for all azobenzene concentrations. In addition in between the α- and the β-relaxation a β′-process is observed for the polymers with the two lowest azobenzene concentrations, which seems to be related to the azobenzene unit. The dependence of the dielectric strength and the relaxation rate of the relaxation processes on the azobenzene concentration is discussed and interpreted in a simple phenomenological model, where also data obtained by semi empirical quantum chemical calculations are used.