SIDE-CHAIN LIQUID-CRYSTALLINE POLYMERS - ELECTRIC-FIELD EFFECTS AND NONLINEAR PROPERTIES

Side chain liquid crystalline polymers offer unique advantages as a new class of organic materials with potential for nonlinear optical response. Synthesis of a number of cyanobiphenyl-based side chain polymers was carried out employing the concept of having the cyanobiphenyl species serve concomitantly as both the linear optical chromophore and the mesogenic moiety in the polymer. The thermal behavior of these polymers was studied by DSC, optical microscopy and X-ray diffraction. Thin polymeric films were spin coated and electric field poling measurements were carried out as a function of temperature. The second harmonic (SH) coefficients d(33) and d(31) were measured by Maker fringe analysis and compared with the values predicted by molecular statistical models. The results showed that one can gain in net polar ordering by starting with a liquid crystalline system. The enhancement in d(33) when < P-2 > approximate to 0,6 was found to be a factor of 2,3-3,3 over the isotropic case (< P-2 > = 0). The relaxation process was investigated. Both the presence of liquid crystal character in the material and the temperature at which the films were stored below Tg appeared important in determining the thermal stability of the SH coefficients.