【作者】 董晓明；

【导师】 魏杰；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2010， 博士

【摘要】 光二聚肉桂酸酯类聚合物在紫外光照下会发生顺反异构变化,同时还可以发生[2+2]环化反应。而这一系列光化学反应,可以引起分子体积的改变,进而改变物质的结构、溶解性、光学性质等诸多方面,且相较于光异构的可逆性具有稳定性,从而使得光二聚肉桂酸酯类聚合物具有更为广泛的应用前景。近年来,光控取向材料成为当前的研究热点,人们发现通过偏振紫外光照射,引发聚合物薄膜的光异构、光交联和光降解,产生表面各向异性,使得液晶分子在薄膜上发生取向排列。本文提出与上述光控取向完全相反的思路—光控解取向。将光活性基团引入光学各项异性材料,制备光敏各项异性材料。随后通过紫外曝光,引发光敏各项异性材料局部的光异构或光交联,实现对光敏各项异性材料进行光控解取向,得到具有不同相位差的图像。围绕肉桂酸酯类聚合物的光二聚机理,系统研究其光化学行为；对紫外光肉桂酸酯类聚合物和聚乙烯醇类感光高分子的记忆效应进行了详细研究。首先,我们通过实验证明了自由基并不会引发肉桂酸酯的光二聚反应反应。紫外光谱分析可以对肉桂酸酯光化学反应进行动力学分析。肉桂酸酯稀溶液在紫外曝光下只发生顺反异构反应,且为一级对行反应。肉桂酸衍生物晶体的光化学反应以光二聚为主。肉桂酸衍生物的液晶类型态对其液晶态的光化学反应有重要影响。对了解肉桂酸酯光二聚机理有很大的帮助。然后我们以此为指导分别从有机液晶分子及感光高分子两个方面探讨了肉桂酸基团在光控解取向记忆效应领域的应用。制备了肉桂酸酯功能液晶,并研究其记忆效应。光二聚合成的肉桂酸胆甾醇酯制备了二苯基环丁烷二羧酸二胆甾醇酯,并利用液晶记忆效应实现了信息记录。热力学研究表明,有刚性链的中等分子量液晶的结晶温度,随着降温速率的加快,明显下降。足够高的速率降温,会使结晶温度低于玻璃化温度,从而导致处于液晶相的化合物在降至室温时,形成玻璃态液晶,而非结晶。实时广角X射线衍射的测试数据也支持了该机理解释。研究了光敏高分子光控解取向与偏光记忆效应。成功搭建一套具有偏振光可控光路系统的光化学反应平台。制备聚乙烯醇肉桂酸酯及聚乙烯醇／铜离子薄膜,通过拉伸取向实现各项异性,制得具有双折射效应的感光性高分子膜。然后通过紫外光照,引发光化学反应,明显的降低了高分子薄膜取向度,实现高分子的解取向。提出了光弹性率的概念,并通过带有偏振棱镜的分光光度计研究了感光高分子的偏光特性和记忆效应,建立了光弹性率量化模型。更多还原

【Abstract】 Cinnamoyl moiety could both be photoisomerized and [2+2] cyclized under UV irradiation. These photoreactions could make changable molecular volume which was independent of heat. Thus, cinnamoyl moieties could be applied widely. Photosensitive polymer chains could be oriented by exposed to the linearly polarized ultraviolet light. Since this was reported, a considerable amount of research has been directed towards photo-induced liquid crystal alignment. Photo-orientation becomes a new investigative hotspot because it is an important part of photo-induced liquid crystal alignment. Conversely, photo-de-orientation mechanism was presented in this study. Photosensitive anisotropy materials were synthesized, exposed by UV light and de-oriented because of either photoreaction, then images of difference phase were prepared. Photochemistry Behaviors of cinnamoyl moiety and memory efects of cinnamoyl moiety and PVA were systematicly studied.Results of experiments demonstrated that the existence of free radical initiator could not initiate photodimerization of cinnamoyl moieties. UV-Vis spectral analysis was used for studying the kinetic behaviors of cinnamoyl moiety photoreaction. The photoreaction kinetics of cinnamoyl moiety in solution fit to first order excellently. Cinnamoyl moiety in solid state only involves photodimerization. Different phases of liquid crystal would influence photoreactions of cinnamoyl moiety in liquid crystal phase hugely. These investigations have enabled us to present new data and interpretations regarding the [2+2] photocycloaddition reaction. What’s more, it can also be used to analyze the photoreaction of the C=C bond which is expected to control the reflected band and the color of cholesteric liquid crystals. The investigation was taken as the guidance to study memory effects of cinnamoyl moieties, from both liquid crystal and photosensitive polymer.Cinnamoyl moiety liquid crystal was synthesized and memory effect was studied. Dicholesteryl diphenyl cyclobutanediate was synthesized by photodimerization of cholesteryl cinnamate. Glassy cholesteric liquid crystal was prepared. The test showed it could be used as a rewritable color recording material. The principle of glassy liquid crystal was discussed. In-situ studies of structural and morphological changes during the process forming glassy liquid crystal were carried out using synchrotron wide-angle X-ray diffraction (WAXD) techniques and DSC. It can be concluded from DSC and synchrotron WAXD that the crystallization peak moves from high temperature to low temperature with the increasing cooling rate. If the cooling rate is fast enough, it can make the glass transition temperature higher than the crystallization temperature. Thus, glassy liquid crystal was vitrified instead of becoming into crystal state and the cholesteric color was fixed.Photo-de-orientation and memory effect was studied. UV-Vis spectrophotometer with polarization adjunct was used to measure the polarization character of photosensitive film. The Poly (vinyl cinnamate) (PVCi) film and PVA/Cu2+ film were prepared. They were stretched and photoelastic birefringence formed. Then the oriented films were exposed to UV light. The birefringence decreased under the UV irradiation. The results can be obtained quantitatively by a measurement using polarization spectrometer. The conception of birefringence ratio was presented. The birefringence ratio quantization model was established and the model was attested by experiments.更多还原