Synthesis And Properties Of Silicon-based Functional Materials By Thiol-ene Click Chemistry

To compare with other materials, silicone materials as a kind of newly functional materials have their incomparable advantages. Due to their high and low temperature resistance, aging resistance, electrical insulation, corrosion resistance, and physiological inertia and so forth, silicone materials are widely used in aerospace, biomedical, architecture, environment, energy, electronics and other fields. Hydrosilylation reaction based on silicon-hydrogen bond and unsaturated double bond is an important and the most used organic reaction in the preparation of all kinds of amphiphilic silicone materials. The reaction has some advantages:broad applicability, rich products, and less side effects. However, it has some inevitable shortcomings, such as needing to use the precious metal as a catalyst, harsh reaction condition, long reaction time. It is important, therefore, to develop a new method or technology with rapid, efficient, and atomic economic on the development and application of newly functional silicone materials. In this paper, a series of silicone-based amphiphilic polymers are fabricated via a facile and efficient thiol-ene click chemistry method and their self-assembly properties in aqueous solution are studied in detail. The main work includes the following several aspects:1. The excellent properties, preparation methods and applications of typical silicon-based polymers, polysiloxane and polysilsesquioxane,are introduced in detail. Then, the progress in preparation and application of silicone-based materials are discussed seriously. Finally, the research objectives and main research contents in the current paper are presented.2. A facile and efficient synthesis of polysiloxane-based amphiphilic copolymer are fabricated via thiol-ene click chemistry. The properties of PEG-b-PDMS-b-PEG and PDMS-g-PEG(20) and PDMS-g-PEG(100) amphiphilic copolymers are studied in detail by a combination of 1H NMR, FT-IR, gel permeation chromatography, and thermogravimetric analysis. In comparison with the traditional hydrosilylation method which requires noble metal catalyst platinum, the newly designed thiol-ene protocol produces polysiloxane-based amphiphilic copolymer with only anti-Markovnikov addition products under benign conditions. The resulting copolymers have lower critical aggregation concentration (CAC) with corresponding value 1.2×10-2 g/L to 6.8×10-3 g/L, and dynamic light scattering (DLS) results revealed that the obtained amphiphilic copolymers can self-assemble into nanoparticles in aqueous solutions with a narrow size distribution (PDIs are less than 0.23). Thermal analysis results show that the copolymer has good thermal stability, and the decomposition temperature is depended on the content of polysiloxane.3. The structure and electronic properties of polyhedral oligomeric silsesquioxane (POSS) cages functionalized with mono-substituted and multi-substituted vinyl and mercaptopropyl have been studied using density functional theory calculations. Electron density distribution and frontier molecular orbitals (FMOs) have been constructed at B3LYP/6-31+G(d) level to understand the electronic properties.1H,13C, and 29Si NMR spectra by using gauge including atomic orbital (GIAO) method of studied compounds were compared with experimental data obtained. The results indicate that the theoretical calculation results are indentical with the experiment. And the current method provides a theoretical guidance for design and special application of the functional POSS compounds.4. There amphiphilic octasubstituted polysilsesquioxane polymers POSS-PEG (PPA, PPB, and PPC) are prapared via thiol-ene click chemistry. The stuctures and properties of the three amphiphilic polymers are characterized in detail by a combination of 1H NMR,13C NMR,29Si NMR, FT-IR, and gel permeation chromatography. Thermostability and self-assembly behavior in aqueous solution are investigated by thermogravimetric analysis and fluorescent probe technique. Thermal analysis indicate that polymers have excellent thermal stability and the existence of thioether bond does not affect their thermal stability. DLS results show that this kind of amphiphilic polymer can directly self-assemble to form stable nanometer particles with bimodal distribution in aqueous solution, and the particle size, which is independent with the polymer concentration, is about 7 nm and 210 nm, respectively. The results of light transmittance test show polymer PPC has acute responsive to temperature. When the temperature rises to 45.5℃, the solution sharply turned into white cloudy, and the range of transition temperature is less than 2℃.