紫外光对有机修饰硅氧烷Sol-Gel过程的影响研究

【作者】 李伟；

【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， 2010， 硕士

【摘要】 有机硅氧烷是有机-无机杂化材料合成领域中的一类重要前驱体。其在不同条件下发生水解-缩合反应,通过溶胶-凝胶过程可以制备出多种结构各异、性能多样的杂化材料。这类杂化材料因其化学性质稳定、光学透明以及机械性能方面的优越性而被广泛应用于光学器件、电子元件、生物医学传感、催化、功能涂层和薄膜等领域,是当今材料科学领域的研究热点之一。尽管人们发现,紫外光辐射在利用硅氧烷的溶胶-凝胶过程制备有机-无机杂化材料上存在着传统热处理所没有的众多优势,例如固化迅速、可室温下操作、能耗低、污染小以及产物结构和性能更加优异等。通过传统溶胶-凝胶法制备的材料在后期的干燥和热处理过程中,缩合作用受到影响从而导致产物性能出现缺陷,而同等条件下光照处理的产品则能够有效的避免或减少这一缺陷。但大部分有关紫外光辐射对硅氧烷的溶胶-凝胶过程研究都集中在材料制备方面,且多数研究者认为光照能促进硅氧烷的水解和缩合反应,从而引起有机基团光解使其发生结构重排。然而,对于机理的研究还没有定论。同时,在含有双键的可聚合有机硅氧烷研究中,多注重光敏剂存在下的光引发有机端烯键聚合,而往往忽视紫外光辐射对无机端水解-缩合反应产生的影响。鉴于有机端含有可聚合烯键的甲基丙烯酸丙酯三甲氧基硅烷(3-Methacryloxypropyltrimethoxysilanesilane, MAPTMS)的广泛应用,拟通过对其在紫外光照与非光照条件下水解-缩合反应的比较性研究,揭示紫外光对有机硅氧烷水解-缩合反应的作用机制。这些研究结果无疑对优化杂化材料合成条件以及材料的可控性合成均具有重要的理论意义与应用价值。正鉴于此,本论文开展了以下两部分研究工作：第一,以甲基丙烯酸丙酯三甲氧基硅烷、辛基三甲氧基硅烷和丙基三甲氧基硅烷三种典型的有机硅氧烷作为前驱体,利用荧光探针技术、ATR-IR、1H NMR、13C NMR以及29Si NMR等手段对比性地在线追踪了三种前驱体在紫外光照与非光照条件下的水解-缩合反应过程。荧光探针实验结果表明：与非光照体系相比,芘在含疏水性取代基的有机硅氧烷水解-缩合体系中的基激缔合物荧光特征峰在反应前期明显而快速增长,而后期逐渐减弱。该结果间接表明紫外光对水解和缩合反应均具有促进作用。红外光谱结果表明：紫外光辐照有机硅氧烷体系,反应前期的Si-OH特征峰随时间明显增加,反应后期Si-O-Si特征振动峰明显增加。说明紫外光辐照有利于水解和缩合反应进行。Si相关物种的29Si NMR结果表明：非光照体系的水解和缩合反应几乎是伴随发生,因而主要形成线性的Si-O-Si链,交联产物相对较少。从体系的宏观表现而言,即使体系反应数月甚至一年尽管粘度增加,但未发现胶凝现象。相反,光照体系使交联相关Si物种的特征信号明显增加,且在宏观上表现出短时间内的胶凝现象。同时,含可聚合双键的MAPTMS体系红外光谱检测结果表明：在紫外光辐射下,其分子中的双键并未发生显著变化。热分析结果也从侧面证明有机取代基未发生明显分解。上述研究结果表明：紫外光辐射对有机硅氧烷水解-缩合反应的促进作用主要发生在无机端。其主要特征是：紫外光辐射可促进前驱体水解反应更完全,形成易于交联的相关物种,最终导致有机硅氧烷体系胶凝。第二,研究紫外光辐射对有机硅氧烷水解-缩合反应的影响与自由基间的关联性。可提供羟基自由基的Fenton反应体系可以使难于胶凝的有机硅氧烷在很短时间内胶凝,且形成坚硬而透明的材料,该结果显示：羟基自由基具有促进硅氧烷溶胶-凝胶体系的胶凝化；在紫外光辐射含强荧光特性Ce3+的MATPMS水解-缩合体系时,荧光强度显著降低,这一结果表明：具有荧光特性的Ce3+被氧化成无荧光特性的Ce4+。说明紫外光辐射体系含具有氧化性的自由基；当体系存在自由基清除剂肾上腺素时,紫外光辐照体系凝胶作用被明显阻碍,上述实验结果间接地证明了紫外光促进有机硅氧烷体系的凝胶作用与其引发自由基的存在有明显关联性。即紫外光辐射和自由基对于硅氧烷Sol-Gel过程的作用具有一定的等效性。本研究工作为紫外光辐射促进有机修饰硅氧烷Sol-Gel过程的机理探讨提供了极具价值的信息。更多还原

【Abstract】 Organically Modified Siloxane is one of the most important precursors to prepare organic-inorganic hybridized materials. Many hybridized materials with a great diversity of structure and property have been synthesized through sol-gel process of organically modified siloxane. Based on the outstanding properties of this kind of materials in chemical inertness and optical transparency, this kind of materials have been widely used in optical and electrical materials, biomedical/medical sensors, catalyst, multifunctional coatings and films etc. Therefore, the researches related to the fundament and applcation of organically modified siloxane have been extensively concerned.The fact that sol-gel process of siloxanes treated with UV-irradiation has some advantages in preparation of organic-inorganic hybridized materials compared with traditional heat-treating has been found. The traditional heated treatment could make the crystal structure of products defective but UV-irradiation could avoide or decrease the defects efficiently. Most researchers speculated that the irradiation could enhance the hydrolysis and condensation of siloxanes due to photodegradation of the organic group and structural rearrangement. However, the mechanism regarding the process mentioned above is scarcely found in literatures. To get some information about the mechanism, octyltrimethoxysilane (OTMS), propyltrimethoxysilane(PTMS) and 3-methacryloxypropyltrimethoxysilanesilane (MAPTMS), the useful precursores, were selected, and the influences of UV photo-irradiation on the sol-gel process of the three precursors in molecular scale have been investigated by using various techniques including fluorescence spectrum, ATR-IR,1H NMR, 13C NMR and 29Si NMR. Based on the investigation of this research, the following results were obtained.First, the sol-gel processes of OTMS, PTMS and MAPTMS in HCl aqueous solution were respectively traced by fluorescence spectroscopy, ATR-IR,1H NMR,13C NMR and 29Si NMR. The results show that UV-irradiation could enhance the rates of hydrolysis and condensation of the three precursors throuth promotion of the complete hydrolysis of precursors and followed by the cross-linked condensation between the hydrolyzed products with multiple Si-OH groups. As a result, the corresponding gels quickly formed. According to the results from ATR-IR,1H NMR, and 13C NMR, the hydrolysis and condensation reactions of the siloxanes were dominant in presence of UV-irradiation. There are many Si-OH groups produced firstly and followed by the formation of Si-O-Si bonds. The 29Si NMR indicated that the condensation reaction accompanied with the hydrolysis reaction for the UV free system but the hydrolysis was predominant firstly to form the hydrolyzed species with multiple Si-OH groups and followed by cross-linked condensation. For UV free system, the lineary condensation products are dominant. For UV system, the cross-linked condensation products are preponderant.Second, based on the results from this research, some information about the mechanism on the effect of the UV-irradiation on the hydrolysis and condensation of organically modified siloxane were obtained. It was obseved that the siloxanes were easy to gel in presence of Fenton reagent containing free radicals. The results from the fluorescence probe of Ce3+ showed that the fluorescence intensity markedly decreased in presence of UV-irradiation, implying that Ce3+ was oxidized to Ce4+ without fluorescence by the free radicals produced by UV-irradiation. Interestingly, the scavenger of free radicals, adrenaline, was added to the UV-irradiation system to result in distinct retardation of the gelation. All aforementioned results indirectly proved that the effect of UV-irradiation on the gelation of organic siloxane is attibuted to free radical induced by UV-irradiation.All of the results in this research afforded some extremely valuable information on the mechanism of UV-irradiation promoting the hydrolysis and condensation reactions. It is sure that UV-irradiation and free radical are equivalent to influence the hydrolysis and condensation reactions of organic siloxane.更多还原