Alternate synthetic approaches for second-order nonlinear optical polyimides

Two alternate synthetic routes for nonlinear optical (NLO) polyimides are suggested, in which the drawbacks of previous methods were overcome. Two types of NLO-functionalized polyimides were prepared by simple one-pot Mitsunobu reaction between NLO-diol compounds and diimides. In addition, three functionalized second-order NLO polyimides were synthesized by step polymerization reaction between a chromophore-containing dianhydride and three different diamine compounds. This alternate approach, incorporating a nonlinear chromophore into a dianhydride monomer, may avoid the troublesome synthesis of the chromophore-containing diamine and can simplify the preparation of polyimides with various chromophores. The polymers prepared from these new synthetic routes have been characterized by physico-chemical technique, especially the second harmonic generation (SHG) method. They showed high nonlinearity and good orientational stability of the aligned dipoles.