Synthesis and optical properties of polyurethanes containing a highly NLO active chromophore

Abstract

Two types of new polyurethanes with a highly NLO active chromophore, 2-[4-[4-[bis(2-hydroxyethyl)amino] phenylazo] benzylidene] malonitrile (HAPM), in the polymer side chain were synthesized (PU1-DCN and PU2-DCN) and characterized. The diisocyanate components of the polymers are 2,4-tolylene diisocyanate and 3,3'-dimethoxybiphenyl-4,4'-ylene diisocyanate. The molecular weights of PU1-DCN and PU2-DCN were determined to be <(M)over bar (w)> = 23000 (<(M)over bar (w)>/<(M)over bar (n)> = 2.19) and <(M)over bar (w)> = 22000 (<(M)over bar (w)>/<(M)over bar (n)> = 2.34), respectively. The final products are readily soluble in polar aprotic organic solvents, like tetrahydrofuran, N,N-dimethylformamide, cyclohexanone, etc. Good optical quality films were obtained by spin coating. The glass transition temperatures of both polymers were found to be 158-159 degrees C. They showed no melting points in the DSC curves, suggesting an amorphous phase. It was found that the electro-optic coefficient of PU1-DCN was r(33) = 62.7 pm.V-1 at 633 nm wavelength. The macroscopic second-order hyperpolarizability at 1064 nm wavelength was determined to be chi((2)) = 136 pm.V-1 for PU1-DCN and chi((2)) = 120 pm.V-1 for PU2-DCN.