The present invention concerns a process for realization of polymeric materials with second order nonlinear electro-optical properties comprising the following steps: mixing of a chromophore with nonlinear optical properties with two or three hydroxy groups; isolation of said pure bi- or tri-isocyanate NLO chromophores obtained according to the above step; dissolution of said bi- or tri-isocyanate NLO chromophores obtained according to the above step in one or more isocyanate group not reactive solvents containing reactive substances; coating of a thin layer of said prepolymer mixture on a substrate and evaporation of said not reactive solvents; cross-linking and poling of said thin layer on substrate, by means of heating and application of an electric field; cooling of said thin cross-linked and poled layer at ambient temperature maintaining the applied poling electric field; switching off the poling electric field.