Synthesis of Novel p-π Conjugated Graft Poly(Amic Acid)s and their Third-Order Nonlinear Optical Properties

Abstract

A novel p- π conjugate poly(amic acid) (PAA) was synthesized by the polycondensation of benzoguanamine (BGA) and pyromellitic dianhydride (PMDA) under microwave irradiation. The PAAs were grafted with toluene isocyanate-aliphatic alcohol derivatives with varying alkyl chain lengths. The solubility of the grafted PAAs improved and the degree of electron delocalization along the polymer chain increased. The third-order nonlinear optical (NLO) properties of these graft polymers in both solution and solid state (i.e. thin films) were measured by the degenerated four wave mixing (DFWM) technique. The effects of alkyl chain length of the graft on the third-order NLO coefficient to polymers backbone were investigated. The extension of the conjugate length and relatively high electron densities of polymer chains contributed significantly to the enhancement of the NLO properties. The third-order NLO coefficient of polymer films was much higher than that in solution.