Synthesis and characterization of novel multifunctional high-Tg photorefractive materials obtained via reactive precursor polymers

We describe the synthesis of a new class of high-T-g multifunctional photorefractive polymers. They were obtained by radical copolymerization of methyl vinyl isocyanate and various N-substituted maleimides. Hole transporting carbazole moieties were attached though a variety of alkyl and phenyl spacers to the imide positions of the maleimides. In a polymer analogous reaction the reactive isocyanate groups of the precursor polymers were reacted with different; hydroxyalkyl-terminated nonlinear optical chromophores. Two azo chromophores including dispersed red-1 and one pyrazolone dye were used. The resulting materials have been characterized by means of GPC. DSC, and UV/vis spectroscopy. All materials are amorphous and possess excellent solubility in common solvents such as chloroform and THF. Molecular weights range between 20 and 272 kg/mol. The glass-transition temperatures vary between 60 and 194 degrees C, depending on the length and the nature of the spacer groups between the maleimide rings and the carbazole moieties. Chromophore contents up to 44 mol % have been realized. Holographic experiments were performed on a device made from a multifunctionalized PR polymer plasticized such that the glass-transition temperature was T-g = 80 degrees C. The material was prepoled Co break inversion symmetry and to induce macroscopic electrooptical properties. The steady-state gain coefficient (approximate to 7 cm(-1)) and diffraction efficiency of this device (approximate to 1%) were reduced compared with that of low-T-g materials. This is because orientational enhancement effects observed in low-T-g materials are excluded in tale high-T-g regime. For the grating formation a dominant response time tau(1) = 100 ms was found.