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

A novel series of main-chain polymers from LAMBDA-shaped molecules were synthesized by nucleophilic displacement polymerization. These polymers were prepared from bis(4-fluoro-3-nitrophenyl) sulfone with aliphatic and aromatic diamines in aprotic solvents. These main-chain polymers derived from LAMBDA-shaped molecules are amorphous, processable, contain high density of nonlinear optical-active chromophores, and exhibit high glass transition temperatures. The corona discharge poled polymer 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 still larger than those of n(TM). The large positive birefringence indicates a preference of polymer chains to orient along the film surface.