Pressure Effects on the Thermal Z/E Isomerization of 4-(Dimethylamino)-4'-nitroazobenzene in a Liquid Polymer. A Comparison of Dynamic Solvent Effects in Polymerie and Monomeric Solvents

Effects of pressure on the thermal Z/E isomerization of4-(dimethylamino)-4'-nitroazobezene were studied in a silicon oil at various temperatures. The results were compared with the ones previously obtained in glycerol triacetate (GTA) and 2-methylpentane-2,4-diol (MPD).Even in the polymer, pressure effects expected from the transition state theory were obtained at low pressures (P < 200 MPa).However, as in GTA and MPD, the transition state theory became invalid at higher pressures. For the polymeric liquid, the macroscopic shear viscosity obviously does not suffice for a quantitative description of the microscopic frictions between the reactant and the solvent molecules.