Dielectric relaxations of some maleimide derivatives and their mixtures with methyl methacrylate

Abstract

The dielectric loss Δε″/x was measured for dilute solutions of some N-substituted maleimides in CCl 4 and benzene in the frequency range from 0.2 to 18 GHz and temperatures between 20°C and 40°C. Methyl methacrylate was chosen for the investigation as a polar donor together with N-substituted maleimides which act as polar acceptors. The data for the monomers and the binary mixtures were analyzed by the sum of two Debye terms [sometimes one term]. The first absorption region could be attributed to the molecule as a whole, either for the pure monomer, or for their mixtures with other monomers. These monomers and their binary mixtures could have a second higher frequency absorption region which is associated with the segmental motion of the molecule. The thermodynamic parameters ΔF,ΔH and ΔS which represent the change of free energy, activation energy and entropy respectively, were obtained and discussed in terms of the molecular behavior. The variation of the relaxation time τ of the investigated mixtures in CCl4 and benzene as a function of mole fraction shows a deviation from linearity. This deviation was attributed to some sort of molecular interaction which expectedly takes place between donors and acceptors. This assumption also finds further justifications through the values of the free energy ΔF given for the different systems. The ratios between the experimental values of the relaxation times and those calculated from the individual τ when the mole fraction was taken into account are considered to be a measure for such interaction. The equilibrium constant K of the association processes is also studied by means of the dielectric polarization measurements in order to investigate the molecular interaction which might take place between the investigated compounds.