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 o ptimized for longterm stability of the polar order is presented: rigid -rod-like main chain polymers furnished with long alkyl side chains wi th a portion of the side chains being replaced by NLO-active chromopho res were synthesized. The chromophores are rigidly attached to the mai n chains, normal to the direction of the polymer backbone. In this par ticular geometry the motion of the NLO-active chromophores is restrict ed to a two-dimensional rotation around the stiff main chain. X-ray di ffraction experiments on spin-cast films of the polymers show a lamell ar structure with a preferential orientation of the layers parallel to the substrate plane. The incompatibility of polar main chains and non polar side chains leads to this microphase segregation. This layered s tructure improves the long term stability of polar order in the poled polymer film. Dielectric spectroscopy revealed only one relaxation pro cess of large dielectric strength. The Arrhenius-type temperature depe ndence of relaxation times indicates a locally activated motion of the chromophores.