| Polydimethylsiloxanes (PDMS) are an unique class of polymers that can be crosslinked to form elastomers with many attractive properties, including low surface energy, low toxicity, high optical transparency, and good chemical and thermal stabilities. They have been extensively used in electrical-insulating products, sealing products as well. Most polydimethylsiloxanes today are reinforced with inorganic fillers because of the weak linkages between PDMS molecules. One of the main fillers, aerosilica, with smaller particle size, is easy to aggregate and is difficult to disperse in the silicone rubber matrix.Polymer-layered silicate nanocomposites represent a new class of organic /inorganic hybrid materials, where the inorganic fillers are dispersed into the polymer matrix on a nanoscale. These materials contain a relatively low amount of the layered silicate and often tend to exhibit superior physical and mechanical properties as compared to the corresponding pure polymer. Such improved properties include high strength, high modulus, high heat distortion temperature, increased barrier to gas and solvents, increased flame resistance, as well as electronic and optical properties, and make these materials attractive for a number of applications, especially due to the low cost of the nanofiller, and the small amounts required.In this works, two novel classes of organic agents , [3-(trialkoxysilyl) propyloctadecyl dimethylammonium chloride ( TPAC) and 2-(Methacryloyloxy)ethyl-dimethyl [3-(trialkoxysilyl) propyl] ammonium chloride (TPAB) were prepared and used as swelling agents to treat Na-montmorillonite (Na-MMT) for forming organoclays. This two kinds of organoclay were characterized by X-ray diffraction (XRD ), infrared spectroscopy (IR) and scanning electron microscopy (SEM). The preparation process and the technical conditions of organo-MMT were studied and optimized.A series of novel exfoliated PDMS / MMT nanocomposite with different structures and properties were synthesized by using PDMS and different organoclays. The methods are in-situ polymerization and intercalated polymerization. The resultsABSTRACTindicate that there are very good compatibilities between MMT and PDMS. Nanoscale silicate dispersion was analyzed by FT-IR, XRD, SEM and transmission electron microscopy (TEM). Mechanical properties and dynamic mechanical analysis( DMA) were measured to assess reinforcement, Solvent uptake analyses were used to evaluate PDMS /silicate interactions and the extent of cure. TGA was also used to measure the thermal stability.It was shown that, the MMT-TPAC in PDMS matrix can increase not only the toughness but also the strength and modulus of PDMS to a great extent. The results proved that the nanometer-scale silicate layers of MMT-TPAC were completely exfoliated in PDMS matrix in the cases of 1 %, 2%, 4 % and 10%. In PDMS / MMT-TPAC system, the physical and mechanical properties reach the maximum value when volume percent of MMT-TPAC is 4% with high-MW PDMS aind volume percent of MMT-TPAC is 2% with low-MW PDMS. The nanocomposites exhibit markedly improved physical mechanical properties as compared with the pure polymer or conventional aerosilica-filled polymer composites. A 223 ~ 305%increase in the tensile strength and a 169% ~ 286%increase in the elongation were found for PDMS/MMT-TPAC as compared to that of pure PDMS. The reinforcing and intercalating mechanism of silicate layers in matrix were discussed. In addition, when the content of MMT-TPAC is 2%, the solvent uptake of PDMS reduces obviously.PDMS grafted by alkene monomers can increase physical mechanical properties of PDMS , but decreased the thermal stability of PDMS. This difficult problem was not solved yet.Two kinds of copolymers PDMS- g - (Methyl methacrylate) MMA and PDMS-g- MMA- acrylonitrile (AN) were prepared using graft copolymers synthetic approaches. A series of novel exfoliated graft PDMS / MMT nanocomposite has been synthesized by graft PDMS an...
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