Uv Radiation On Organic Siloxane Hydrolysis And Condensation Process

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.