Uv Organic Modified Siloxane By Sol-gel Process

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.