This paper discusses the electric birefringence (the Kerr effect) of three fractions of a combshaped polymer with cyanobiphenyl mesogenic groups. It is established that there are two relaxation processes in an isotropic melt of the mesogen close to the transition temperature to the nematic phase. The pretransitional electrooptic properties of all the fractions of the polymer are described in terms of the Landau-de Gennes model. The kinetic parameters of the isotropic and nematic phases are compared.