The constant electric field effect on the dipole moment of a comb-like polymer with chromophore groups in side chains

Physics of molecules

The study of conformational properties and tendency to association for chromophorecontaining comb-like copolymer of β-(3,4-dicyanophenylazobenzenethyazole) methacrylate (A) and amylmethacrylate (B) (1:1) has been carried out. The copolymer AB is of particular interest because of nonlinear optical properties of its films. Dielectric permittivity and dipole moment temperature dependences in dilute cyclohexanone solutions in the temperature range from 20 to 70 °С, in the electric field E ≤ 104 V/cm were investigated by means of static dielectric polarization. It was shown that temperature and concentration dependences of dielectric permittivity for the solvent, copolymer AB, monomer A and polymer B were linear indicating low molecular interactions at temperatures and fields used. The invariable stoichiometry of components in solution for concentration lower than 10–3 mol/mol was proved. The values of dielectric permittivity were extrapolated to infinite dilution and increments α = (∆ε12/∆x2)x2=0 were calculated. The solvent dipole moments were calculated in terms of the Onsager theory whereas dipole moments of AB, A and B were calculated in terms of the Backingham statistical theory of dielectric polarization. Intramacromolecular conformational transition was found to be at ∼40 °C. Dipole moment of A was shown to increase with both temperature and electric field strength. Copolymer side chains trans-location takes place due to intramacromolecular association resulting in the compensation of dipole moments and Kirkwood factor g ≈ 0.6. The association of A units increases in the electric field reducing the dipole moment per monomer unit significantly and g values approximately twice.