Synthesis and characterization of novel polyamides carrying NLO moieties

A series of novel polyamides carrying NLO chromophores were synthesized and their general properties were characterized. The electrooptic properties of a couple of selected compositions were studied. These polyamides were synthesized by direct polycondensation at 100 degrees C of 4,4'-methylenedianiline or 4,4'-oxydianiline with 4-nitro-[N,N-bis(2-carboxyethyl)]aniline or 4-[N,N-bis(2-carboxyethyl)amino]-4'-nitro- stilbene in the presence of a condensing agent composed of lithium chloride and triphenyl phosphite. All of the polymers were found to be amorphous and their glass transition temperatures were about 160 degrees C, In contrast, the polymer that does not carry the nitro group in the phenyl ring of the side group revealed a T-g value of only 78 degrees C. This difference strongly indicates that the nitro group is involved in the formation olf hydrogen bonds and, thus, hinders the chain mobility resulting in the enhanced T,values. This could be confirmed by the i.r.-spectroscopic analysis of the polymers. The u.v.-vis. absorption characteristics of the polyamides also were studied. The second-order nonlinear optical properties of the thin films of two selected polymers of better solubility were studied by measuring their electrooptic coefficients after being poled at the temperatures near their T(g)s. When the polymer films were poled at the field strength of 0.4-0.6 MV cm(-1) their electrooptic coefficients obtained for the incident beam of 1.3 mu m were about 3 pm V-1 and they showed an excellent temporal stability even at 80 degrees C. (C) 1997 Elsevier Science Ltd.