A novel Y‐type polyurethane (polyurethane 3) containing 4‐(4‐nitrophenylazo)resorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute part of the polymer backbone, was prepared and characterized. Polyurethane 3 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It shows thermal stability up to 270 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of 102 °C. The second harmonic generation (SHG) coefficient (d33) of the poled polymer film at 1064 nm fundamental wavelength is 2.06 pm V−1. Polymer 3 exhibits thermal stability up to Tg, and no significant SHG decay is observed below 100 °C, which is acceptable for nonlinear optical device applications. Copyright © 2012 Society of Chemical Industry

Novel X‐type polyurethane 5 containing 4‐(2′,2′‐dicyanovinyl)‐6‐nitroresorcinoxy groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone, was prepared and characterized. Polyurethane 5 is soluble in common organic solvents such as acetone and N,N‐dimethylformamide. It shows thermal stability up to 280 °C from thermogravimetric analysis with a glass transition temperature (Tg) obtained from differential scanning calorimetry thermogram of around 120 °C. The second harmonic generation (SHG) coefficient (d33) of poled polymer film at 1064‐nm fundamental wavelength is around 6.12 × 10−9 esu. The dipole alignment exhibits a thermal stability even at 5 °C higher than Tg, and there was no SHG decay below 125 °C due to the partial main chain character of the polymer structure, which is acceptable for NLO device applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

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Recently, great attention has been focused on the synthesis of nonlinear optical (NLO) materials because of their potential applications in the field of electro-optic devices including ultrafast optical switches and high-speed optical modulators.1-4 NLO polymers have many advantages superior to conventional inorganic ones such as low cost, ultrafast response, wide response wave band, and good processability to form optical devices. One of the current challenges is to design novel NLO polymers having optimized properties. A potential NLO polymer must contain highly polarizable conjugated electronic systems and has to be mechanically very strong and thermally stable with a high glass transition temperature (T g ). In the developments of NLO polymers for electro-optic device applications, stabilization of electrically induced dipole alignment is one of important considerations; in this context, two approaches to minimize the randomization have been proposed, namely the use of cross-linked systems 5,6 and the utilization of polymers with high glass transition temperature (T g ) such as polyimides.7-10 Polyimide materials for NLO applications have attracted attentions because of their high T g and high thermal stability, which can be used to stabilize the dipole orientation of the NLO chromophore at high temperatures. Various type of polyimide-based NLO materials have been synthesized, and their properties have been studied.7-10 There are two types of NLO polyimides, which have been used either as host polymers for composite materials or as matrix polymer backbones for side-chain NLO chromophores. Main-chain NLO polymers have good thermal stability of dipole alignments, but they often do not dissolve in organic solvents, and their intractability make them unusable to fabricate stable noncentrosymmetric films. Side-chain NLO polymer systems have the advantages such as good solubility and homogeneity, but they often suffer from poor stability of dipole alignments at high temperatures. Recently we prepared novel NLO polyimides containing dioxynitrostilbenyl groups 11-13 and dioxybenzylidenemalononitrile 14-17 as NLO chromophores. The resulting polymers exhibit enhanced thermal stability of second harmonic generation (SHG), which stems from the stabilization of dipole alignment of the NLO chromophores. In this work reported here, we prepared new Y-type polyimide containing nitrophenylazoresorcinoxy groups as NLO chromophores. We selected the latter as NLO chromophores because they were expected to have high optical nonlinearities. Furthermore, these groups constitute novel Y-type NLO polyimides, and these Y-type NLO polyimides have not yet been reported in the literature. Thus, we synthesized a new type of NLO polyimide, in which the pendant NLO chromophores are parts of the polymer backbone. This Ytype NLO polymer is expected to have the merits of both main-chain and side-chain NLO polymers, namely stable dipole alignment and good solubility. After confirming the structure of the resulting polymer, we investigated its p...

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