紫外光辐射对有机硅氧烷水解缩合过程的影响研究

【作者】 赵晓辉；

【导师】 胡道道；

【作者基本信息】 陕西师范大学 ， 高分子化学与物理， 2008， 硕士

【摘要】 利用烷氧基硅烷作为前驱体进行溶胶-凝胶反应制备无机氧化物和有机-无机杂化材料应用于光学器件、电子元件、化学传感、信息存储、功能涂层和薄膜等方面是当今非常活跃的研究领域。在有机硅氧烷前驱体中,甲基丙烯酸丙酯三甲氧基硅烷(MAPTMS)由于分子存在形成C-C链的可聚合烯键和形成Si-O-Si键的硅氧烷,而使有关该前驱体的研究被广泛关注,其中以该前驱体为主要成分通过水解和光引发聚合制备有机-无机杂化膜材料是非常重要的研究课题。通过传统的溶胶-凝胶反应制备的材料在反应后期的干燥和热处理过程会对得到的材料产生显著影响,主要表现在干燥和热处理对产物缩合作用产生影响而导致产物性能出现缺陷。而同等条件下采用光照法制得的产品则可以有效的避免或者减少上述缺陷。即光处理和传统的热处理对产物的影响表现出明显的差异。大部分研究者认为造成这种差异性的主要原因在于:(1)光照能加速硅氧烷的水解和缩合反应;(2)光辐射作用可引起有机基团光解而发生结构重排反应。上述作用均被归结为与光照产生自由基有关,但一直未有对这种推测证实性的试验报导。同时,大部分研究集中在光敏剂存在下的光引发有机端烯键聚合,然而,光辐射对无机端的水解缩合产生的影响并未得到关注。基于光辐射对有机硅氧烷水解缩合会产生显著影响的实验事实,其对MAPTMS水解缩合反应产生的影响是不应忽视的。因此,本论文以甲基丙烯酸丙酯三甲氧基硅烷(MAPTMS)为前驱体,对光照和非光照条件下体系的水解缩合作用进行了研究,旨在探讨紫外光辐射与自由基对有机硅氧烷水解缩合反应影响的相关性。为此,本论文开展了相关的工作,主要包括以下两部分内容:(1)以MAPTMS为前驱体,对比性地研究了在光照与非光照条件下MAPTMS在酸性条件下的水解缩合过程。红外光谱、核磁共振氢谱在线检测结果表明:紫外光辐射对MAPTMS无机端的水解缩合反应具有显著的影响,表现为短时间内发生由液体溶胶到固体凝胶的转化;而在非光照的情况下,放置一年的反应体系仍保持液体状态;同时,光辐射并未对有机端的烯键聚合产生显著影响。光辐射可以调节水解与缩合反应的相对速率,具有明显促进前驱体水解而产生较多硅羟基的作用,从而使具有较多硅羟基的水解产物形成高度交联的空间网状结构并最终形成固化产物。在非光照情况下体系水解和缩合反应同时进行,导致前驱体生成不彻底的水解产物,形成的线性缩合物分子缩合程度较低而观察不到胶凝现象的出现。本研究结果对于很难胶凝的MAPTMS形成凝胶和固化状产物具有重要的借鉴意义。(2)研究了自由基对MAPTMS水解体系胶凝行为的影响。利用Fenton反应产生的羟基自由基,考察了羟基自由基对MAPTMS水解缩合反应产生的影响。同时,利用FT-IR和~1H-NMR等表征手段研究了MAPTMS纯品和Fenton试剂与MAPTMS共存时体系的溶胶凝胶反应。结果表明:羟基自由基可以显著促进MAPTMS水解缩合体系的胶凝作用,证实了紫外光辐射与自由基对有机硅氧烷水解缩合反应影响的相关性。更多还原

【Abstract】 It has been an increasing interest in employing Ormosils （Organically Modified Siloxanes） as precursors to prepare various Organic-Inorganic materials through sol-gel processing. Those materials with chemical inertness, mechanical stability and optical transparency are becoming more and more widely used for optical and electrical materials, chemical/biomedical sensors, catalyst, multifunctional coatings and films, and so forth. 3-methacryloxypropyltri-methoxysilanesilane （MAPTMS） has attracted widespread attention because of its special properties. This precursor has two reactive parts in such a way that it offers a two-step polymerization process. A mineral network can be fabricated by hydrolysis and poly-condensation of the sol-gel part of the precursor （-Si （OR）₃） and an organic network can be created by UV photo-polymerization of a double bond present in the R’ group.The heating temperature and atmosphere in the conventional sol-gel process were found to be significant factors affecting the prepared materials via sol-gel process. The usual sol-gel process （heat-treated sample） and a sol-gel process using photo-irradiation （photo-irradiated sample） have different properties on their behaviors. All heat-treated samples included some defects, but the photo-irradiated samples lacked such defects and formed superior structure instead. Most of the researchers hold the reasons as that: （1） it was attributable that the hydrolysis and condensation of silicon alkoxide was accelerated by photo-irradiation. （2） Structural rearrangement reaction can be induced when treated by photo-irradiation through photolysis of the organic group. The effect mentioned above is attributed to the free radicals produced by photo-irradiation. However, most of the researches were focused on material preparation; no final conclusion of progress of reaction kinetics has yet been reached. The photo-assisted sol-gel method is attracting attention for its ability to form inorganic films at low temperature and at low cost. Most of the general work is based on the synthesis of a new generation of organic-inorganic materials whose organic part is photo-polymerized using cationic way. The effect of photo-irradiation on the sol-gel part of the precursor （-Si （OR）₃） is a question not explored before. But as a basic principle of the results of experiments this effect shall not be neglected. But it provided no more structure information on the molecular level which is necessary to study further.According to the information mentioned above, the main contents of this research include two aspects as follows:The first section: A method, employing 3-methacryloxypropyltri-methoxysilanesilane （MAPTMS） as a precursor and HC1 as a catalyst, a comparative study between irradiation and non-irradiation at different times has been carried out. Additionally, the processes of the hydrolysis and condensation of MAPTMS under irradiation and non-irradiation were followed using ¹H-NMR and FT-IR Spectrum. The convert time from sol to gel is very short when the hydrolysis system is treated with ultra-violet light from a high pressure mercury lamp at room temperature. This phenomenon can not be observed under the non-irradiation condition and the system kept flowing even experienced longterm placement. A kind of transparence hybrid material was obtained under irradiation condition. The results indicate that photo-irradiation could affect rates of hydrolysis and condensation of MAPTMS, which promotes formation of condensation product with a network molecular structure. The network molecular structure is related to polycondensation of silanols rather than that of methacryl groups in MAPTMS. The condensation process of the system is accelerated by photo-irradiation by means of regulating the relative reaction rate of hydrolysis and condensation. When treated with photo-irradiation, the system has more completely hydrolytic degree and more silanols. It makes the photo-irradiation system have more opportunity to form branched products to promote gelation occurred.The second section: In order to elucidate the photo-irradiation mechanism of hydrolysis and condensation of MAPTMS, we used Fenton reaction to produce hydroxyl radical to test the postulated reaction mechanism. Based upon the work that the convert time from sol to gel is very short when the hydrolysis system is treated with ultra-violet light from a high pressure mercury lamp at room temperature, the mechanism of this reaction was suggested, which was verified in comparison with the reaction treated with hydroxyl radical produced by Fenton reaction. We put forward the oxidation mode of photo-induced production of free radicals. The processes of the hydrolysis and condensation of MAPTMS treated with hydroxyl radical produced by Fenton reaction were followed using ¹H-NMR and FT-IR Spectrum.更多还原