We present results on nonlinear optical properties of newly-synthesized diazo-dye-substituted methacrylate polymers. These dye-substituted polymers, which have been developed for EO devices, contain a dicyanovinyl-terminated, dimethyl-substituted diazo (3RDCVXY) dye exhibiting a larger hyperpolarizability (beta) than that of nitro-terminated diazo (3RN) or monoazo dye. In order to describe the relationship between a bulk susceptibility (chi) (2) and the (beta) value in the presence of electric poling field, a molecular statistical model is proposed. In the model the intermolecular potential due to the van der Waals forces in transitory aggregates is considered. As the 3RDCVXY dyes, which have the central benzene ring substituted by methyl groups, are prevented to come close to each other, the intermolecular interactions influence more weakly on the 3RDCVXY polymers than the 3RN polymers. As a result, the corona-poled 3RDCVXY polymer exhibits a large (chi) (2) value of 1 X 10-6 esu at 1.06 micrometers , whose thermal stability is excellent even at 80 degree(s)C. The poled 3RDCVXY polymer film exhibits a linear EO coefficient as high as 40 pm/V at 0.633 micrometers . An electro-optical light modulation in the channel 3RDCVXY polymer waveguides with half-wave voltage as low as 5 V is also presented.