CROSS-LINKED POLYMER MATERIALS FOR NONLINEAR OPTICS .2. POLYURETHANES BEARING AZOBENZENE DYES

A cross-linked nonlinear optical urethane polymer is prepared from 4-[(2-hydroxyethyl)sulfonyl]-4'-[N,N-bis(2-hydroxyethyl)amino]azobenzene (1) and toluene diisocyanate by simultaneously corona poling and cross-linking at 145 degrees C for only 30 min. This material shows very promising results as NLO material: SHG measurements show a resonantly enhanced d(33) value of 60 pm/V at 1064 nm 1 day after poling and a 34% decrease after 800 h at 70 degrees C. Moreover, electrooptic measurements on contact poled samples at 175 degrees C result in a value of the pockels constant r(33) of 12.3 pm/V. Poling at 190 degrees C results in a decrease of less than 40 % after 100h at 150 degrees C. Additional measurements show a linear interrelation between the electrooptic and the pyroelectric constant, as well as between the electrooptic constant and the dielectric polarization.