To obtain the in-depth identification of the electronic nature of the substituent effects, which have been recognized as a facilitated means to elevate the second-order hyperpolarizabilities (gamma) of polymers, the systematic quantum chemical studies have been carried out on the tried systems (polyphenyls) of longer chain length (17 phenyl units) and more versatile substitution types (seven kinds) than ever. All polymers are fully optimized and the nonlinear optical properties are based on the finite-field model with PM3 Hamiltonian. The computational results have been validated by available experimental and theoretical data. As found in the experiments, the computed energy levels converge in the range of long chain length, indicating a gradually decreased coupling between components. Both the heat of formations and gamma values of the studied polymers with substituents are found to parallel to those without substituents, which can be explained by the first-order approximation of the additivity law of properties for weakly coupled multi-component systems. This quantitative component effect or the substituent effect may build a theoretical ground to extrapolate long chain polarized polymers on the basis of oligomers. As for the molecular design guidelines, the preferential site for better conjugation, the larger number of substituents, and the more powerful polar groups are favored to elevate gamma.