SYNTHESIS AND CHARACTERIZATION OF NEW PHOTOREFRACTIVE POLYMERS WITH HIGH GLASS-TRANSITION TEMPERATURES

Polyamides based on 2',5'-diamino-4-(dimethylamino)-4'-nitrostilbene ( DDANS) and aliphatic diacids represent a well-established class of pol ymers for nonlinear optical (NLO) applications, in which the NLO units are fixed in the polymer backbone with their dipole moments oriented transversly to the polymer main chain. The introduction of a hole tran sport (HT) agent, [4-((diphenylhydrazono)methyl)phenyl]diethylamine (D EH) or 4-(bis(2-hydroxyethyl)amino)benzaldehyde 1,1-diphenylhydrazone (BBDH), was found to generate or enhance photorefractivity in these ma terials. Using appropriate chemical pathways, the NLO and HT moieties were connected in various ways, and polymer systems with dramatically different properties were obtained. Thus, (i) polyamides based on DDAN S and aliphatic diacids, (ii) polyamide esters based on DDANS, BBDH, a nd adipic acid, (iii) polymer blends of the DDANS polyamides and a pol yester based on BBDH and adipic acid, and (iv) DDANS polyamides doped with DEH have been prepared. All types of polymer systems were process ed into transparent thin films by spin coating and could be oriented a t elevated temperatures, applying a corona discharge poling technique. Second-order NLO coefficients (d(33)) Of UP to 45 pm/V at a fundament al wavelength of 1542 nm have been measured. The poling efficiency was found to depend strongly on the content of the hydrazone moiety and t he polymer system, decreasing with increasing content of hydrazone. Pr eliminary temperature-dependent two-beam coupling experiments demonstr ated photorefractivity for DDANS-based systems, even at temperatures b elow the glass transition.