| The three important developmental periods of the nonlinear optics are reviewed, and the final aim of the study of the nonlinear optics is pointed out; Several new suitable materials should be designed and synthesized because of the limits of the existing materials.The synthesis of the second-order Nonlinear Optical (NLO) polymers is based on the chromophores with large second-order polarizability( β ). A series of AZO chromophores with double or more hydroxyls have been designed and synthesized, which are containing typical donor- π -conjugated-acceptor(D- π -A) structures, and have large β in theory.The second-order polarizabilities of the compound have been determined by Solvatochromic method. It was found by experimental data and calculation that the measured value of β were at 10-28 esu. And the value of β were increased by enhancing the donor strength and increasing the conjugation length between donor and acceptor, moreover, the value would be increased by using pyridine instead of benzene.The poly(urethane-imide)s (PPUI) with a nonlinear optical chromophore in the side-chain were synthesized by a two-step process,. It was found by the study of the thermal properties of PPUI that the initial decomposition temperatures of PPUI were around 300 ℃ ,which were 60℃ higher than those of polyurethanes; And it was observed that the weight of PPUI remained 40% when the temperature were over 770℃.
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