Rigid-Rod-Like Main Chain Polymers with Rigidly Attached Chromophores. A Novel Structural Concept for Electrooptical Materials. 1. Synthesis and Characterization

A structural concept for nonlinear optical (NLO) polymeric materials optimized for long-term stability of the polar order is presented: rigid-rod-like main chain polymers furnished with long alkyl side chains with a portion of the side chains being replaced by NLO-active chromophores were synthesized. The chromophores are rigidly attached to the main chains, normal to the direction of the polymer backbone. In this particular geometry the motion of the NLO-active chromophores is restricted to a two-dimensional rotation around the stiff main chain. X-ray diffraction experiments on spin-cast films of the polymers show a lamellar structure with a preferential orientation of the layers parallel to the substrate plane. The incompatibility of polar main chains and nonpolar side chains leads to this microphase segregation. This layered structure improves the long term stability of polar order in the poled polymer film. Dielectric spectroscopy revealed only one relaxation process of large dielectric strength. The Arrhenius-type temperature dependence of relaxation times indicates a locally activated motion of the chromophores.