The electric birefringence of three fractions of a comb-shaped nematic polymer with different molecular masses, and having cyanobiphenyl mesogenic groups, in the vicinity of the nematicisotropic transition temperature has been studied. It was established that two types of relaxation process exist in the vicinity of the nematic-isotropic transition temperature. The Landau-de Gennes model is adequate for a description of the pretransitional electro-optic properties of all the polymer fractions. At the same time, a comparison of some kinetic electro-optical parameters of low molar mass and polymer liquid crystals of similar molecular structure has revealed essential differences in their values that probably are explained by the hindered rotation of mesogenic groups in the polymer samples.