We have determined the ideal composition of sequenced polyacetylene/polymethineimine copolymers for application as second-order materials. As a result of the interplay between delocalization and asymmetry, there exists for second-order nonlinear optics effects an optimal polyacetylene/polymethineimine composition which is estimated to be between 50% to 66% of polyacetylene. However, the addition of any proportion of polyacetylene between 25% and 75% into polymethineimine already leads to a large increase of the electronic first hyperpolarizability, highlighting the interest of creating such copolymers.