Abstract
New copolyethers were prepared by chemical modification of polyepichlorohydrin and poly(3,3-bis(chloromethyl)oxetane) with the sodium salt of either 4-hydroxy-4′-nitrostilbene or 4-hydroxy-4′-cyanoazobenzene, employing the concept of having the nitrostilbene or cyanoazobenzene species serve concomitantly as both the nonlinear optical (NLO) chromophore and the mesogenic moiety in the polymer. Their thermal behavior was established by means of differential scanning calorimetry (DSC) and optical microscopy. The NLO properties of two nematic copolyethers were studied. The NLO mesogenic groups were oriented by the standard corona poling technique and the degree of axial ordering was determined as a function of poling conditions. The second harmonic coefficients d31 and d33 were measured. The results showed that liquid crystallinity enhances field-induced polar ordering. The ratio d33/d31 was found to be much larger than 3, in agreement with the theoretical models for electric field poling of liquid crystals. We were able to obtain d33 values up to 130 pm/V at λ = 1,064 μm, thus exceeding many values previously reported for second harmonic generation measurements on isotropic polymers containing similar side chain chromophores.
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