LAMBDA-TYPE MAIN-CHAIN POLYMERS FOR 2ND-HARMONIC GENERATION

A novel series of main-chain polymers from LAMBDA-shaped molecules wer e synthesized by nucleophilic displacement polymerization. These polym ers were prepared from bis(4-fluoro-3-nitrophenyl) sulfone with alipha tic and aromatic diamines in aprotic solvents. These main-chain polyme rs derived from LAMBDA-shaped molecules are amorphous, processable, co ntain high density of nonlinear optical-active chromophores, and exhib it high glass transition temperatures. The corona discharge poled poly mer films showed large second-order nonlinear optical coefficients and good temporal stability at elevated temperatures. Before poling, all these polymers show positive birefringence. For polymers having rigid spacer units, even after poling, the refractive indexes of n(TE) are s till larger than those of n(TM). The large positive birefringence indi cates a preference of polymer chains to orient along the film surface.