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

Side chain liquid crystalline polymers offer unique advantages as a ne w class of organic materials with potential for nonlinear optical resp onse. Synthesis of a number of cyanobiphenyl-based side chain polymers was carried out employing the concept of having the cyanobiphenyl spe cies serve concomitantly as both the linear optical chromophore and th e mesogenic moiety in the polymer. The thermal behavior of these polym ers was studied by DSC, optical microscopy and X-ray diffraction. Thin polymeric films were spin coated and electric field poling measuremen ts were carried out as a function of temperature. The second harmonic (SH) coefficients d(33) and d(31) were measured by Maker fringe analys is and compared with the values predicted by molecular statistical mod els. The results showed that one can gain in net polar ordering by sta rting 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 th e isotropic case (< P-2 > = 0). The relaxation process was investigate d. Both the presence of liquid crystal character in the material and t he temperature at which the films were stored below Tg appeared import ant in determining the thermal stability of the SH coefficients.