Synthesis And Properties Of Silicon-containing Polymers Via Thiol-ene Click Chemistry

Thiol-ene reaction, which is one member of the class "click" reactions, proceed under mild conditions in the presence of oxygen, are regioselective, tolerate many functional groups, can be run neat or in benign solvents such as water, and provide quantitative or near-quantitative yields with simple or no chromatographic separation required. The radical-based thiol-ene reaction has been widely used to synthesize dendrimer; functionalize biomolecules, biomacrmolecules, and surface; and synthesize new polymeric materials for applications ranging from soft lithography to porous microparticles.Organosilicon compound is that at least one organic group attach to silicon atom in the compound, which is the one of the fastest growing element-organic chemistry. Organosilicon materials have been widely used in aerospace, electrical and electronics, machinery, construction, transportation, energy and medicine, because of their distinctive properties, such as resistance to high temperature, moisture, electrical insulation, corrosion resistance, anti-aging and physical inertia and so on. Generally, functional organosilicon products are prepared via the hydrosilylation reactions in the presence of platinum or rhodium complexes. However, this reaction suffers from some deficiencies. For example, the heavy metal Pt catalysts are expensive, and the functional groups (-OH,-NH2, and-COOH) disturb the catalytic activity of Pt. Furthermore, when the functional organosilicon products are applied in biological and medicinal fields, the metal catalysts should be avoided. Therefore, a new general synthetic strategy to prepare functional organosilicon products is necessary.In this dissertation, valuable explorations have been carried out and focused on the synthesis and properties of organosilicon functional polymers via thiol-ene click chemistry. The main contents are as follows:1. Polysiloxanes are unique hybrid inorganic and semi-inorganic polymers that have a wide range of applications in industries. In this study, we report a facile and efficient approach to prepare functional polysiloxanes via thiol-ene reaction. The functional polysiloxanes were characterized and confirmed by1H NMR,13C NMR, FT-IR, GPC, TGA and DSC. Influence of thiol and vinyl structures on reaction rate was analyzed. The proportion of α-and β-addition products was also determined by1H NMR. GPC analysis showed that the molecular-weight distribution of polysiloxanes can not be disturbed in thiol-ene reaction. The thiol-compounds and vinyl functional polysiloxanes are commercially available at low cost and this method is easily scaled up. Compare with the traditional hydrosilylation reaction, this approach is carried out without metal catalysts under mild conditions and thus the resulting functional polysiloxanes have potential applications in the fields of biology and medicine.2. The novel hyperbranched organosilicon polymers were successfully prepared via step-growth thiol-ene click reaction using mercaptopropylmethyldiallylsilane (AB2) and mercaptopropyltriallylsilane (AB3) as hyperbranched monomers. The structures of the prepared polymers were characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The degree of branching (DB) of the polymers was determined using quantitative29Si NMR spectroscopy. The DB of the polymers from AB2and AB3were0.60and0.22, respectively. The refractive index of PI and P2were1.5269and1.5386, respectively, thereby making them possible candidates as crosslinkers of methylphenyl silicone rubber. Compared with the thermal stability of similar known carbosilane dendrimers, that of the resulting hyperbranched polymer was not affected by the thioether bond. In addition, the resulting hyperbranched polymer can be modified via thiol-ene reaction. These polymers can be attractive candidates for complexing heavy metal ions because of the presence of the thioether bond.3. The multifunctional octasilesesquioxanes have been obtained by photoinduced thiol-ene reactions of octavinyl polyhedral oligomeric silsesquioxane (POSS) with a variety of commercially available multifunctional thiol compounds. Their structures were characterized by FTIR, NMR, ESI-MS and elemental analysis, and their thermal stability was also evaluated by TGA. The obtained multifunctional POSS can provide more active site, which is important in catalysts and biology. In addition, they also can be the precursor to prepare POSS-core dendrimers or organic-inorganic hybrid materials.4. A novel type of UV-curing silicone rubber was prepared via thiol-ene click chemistry by using polydimethylsiloxane containing vinyl groups as a gum, polymercaptopropylmethylsiloxane as crosslinker, TS-530SiO2as reinforcing filler and2,2-dimethoxy-2-phenylacetophenone as photoinitiator. The obtained silicone rubber from thiol-ene curing system was transparent and the SEM analysis clearly evidenced that no obvious phase-separation was observed. The thermomechanical properties of resulting silicone rubber, including the glass transition temperature (Tg) as well as tensile and compressive modulus, were studied using dynamic mechanical analysis (DMA). Meanwhile, the mechanical property, thermal stability and the average molecular weight between crosslinking points (Mc) of the silicone rubber were also determined. Experimental results showed that the thiol-ene click reaction can be used as the alternative curing system to prepare the silicone rubber.