POLYAMIDES ALTERNATELY SUBSTITUTED WITH AN ALIPHATIC CYCLIC MOIETY AND AN NLO-PHORE FOR 2ND-ORDER NONLINEAR OPTICS

This article describes the synthesis and second-order nonlinear optica l (NLO) properties of polyamides containing an alternating arrangement of cholesteryl or menthyl moieties and an NLO-phore, i.e., N,N-dialky l-4-nitroaniline, in the side chain. The poly amides were prepared by condensation polymerization of 5-[2-(N-methyl-4-nitroanilino)ethoxy]is ophthaloyl chloride with cholesteryl (P1) or L-menthyl (P2) 3,5-diamin obenzoate. The resulting polyamides PI and P2 exhibit high glass trans ition temperatures (T-g) around 200 degrees C and good solubilities in common organic polar solvents. Optical-quality films of P1 and P2 wer e obtained by spin-coating. The second harmonic generation (SHG) measu rements of the spin-coated films of P1 and P2 were carried out by the Maker fringe method using a Q-switched Nd:YAG laser (1064 nm) as excit ing beam after corona-poling; they indicate that P1 and P2 exhibit a s econd-order NLO coefficient, d(33), of 10 pm/V. The orientational beha vior of the NLO-phores in P1 is specific for the poling process. A non centrosymmetric alignment of the NLO-phores in P1 was induced by coron a-poling at a temperature lower than T-g, i.e. at 100 degrees C. Addit ionally, it was found that the noncentrosymmetric alignment of NLO-pho res in P1 is inhibited over 160 degrees C due to the para-crystalline aggregation of cholesteryl moieties as deduced from the SHG measuremen ts and X-ray diffraction analysis.