Main-Chain Nonlinear Optical Polymers With Enhanced Orientational Stability

Polyamides based on 2',5'-diamino-4-(dimethylamino)-4'-nitrostilbene (DDANS) and aliphatic diacids, and polyamideesters based on DDANS, 4-(bis(2-hydroxyethyl)amino)-benzaldehyde-1,1-diephenylhydrazone (BBDH), and adipic acid represent a promising class of polymers for nonlinear optic (NLO) and photorefractive applications, where the nonlinear optical units are fixed in the polymer backbone with their dipole moments oriented transversely to the main chain. The orientational relaxation behavior of a series of random copolymers and block copolymers was investigated at different temperatures below the glass transition by the decay of the nonlinear optical susceptibilities of corona-poled thin films. The time dependence of the decay was found to be well represented by the Kohlrausch-Williams-Watts stretched-exponential function. The temperature dependence of the decay could be correlated with the glass transition temperature T-g using a normalized relaxation law with (T-g - T)/T as the relevant scaling parameter. The investigation of the thermal stability of the NLO-phore received special attention in this study. The main-chain polymers investigated exhibit an enhanced orientational stability when compared to side-chain or guest-host systems.