Leonova N. Synthesis, structure and properties of epoxy-silica nanocomposites obtained by cationic polymerization

Object: The structure formation and properties of epoxy polymers and epoxy-silica composites obtained by cationic polymerization of epoxy matrix and by in situ sol-gel synthesis of silica filler. The goal of the research: synthesis of epoxy-silica composites of cationic polymerization with high level of performance properties using in situ sol-gel method for silica particles synthesis. Methods: IR-spectroscopy; differential scanning calorimetry; sol-gel analysis; thermomechanical analysis; differential thermomechanical analysis; scanning electron microscopy; transmission electron microscopy; method of small-angle X-ray scattering; dynamical mechanical analysis; gas-volumometric analysis; derivatography; method of lattice cuts; potentiodynamic method; gravimetric method. Microhardness and impact strength of the obtained polymers, and composites were determined. Results: The regularities of formation and the structural features was established and the properties of epoxy-silica nanocomposites of cationic polymerization using sol-gel method for synthesis of silica particles and catalysts of cationic polymerization-complexes of boron trifluoride with protonos donors was studied. The schemes of synthesis of nanocomposites which provide the removing of products of the tetraetoxysilane hydrolytic polycondensation, alcohol and water, including evaporation from the surface layer of the thin coatings were proposed. It is found that the fractal type structures from primary silica particles with the size of 4-14 nm are formed in the polymer matrix, in this the size of the nanoparticles grows with the increasing of fillers content. The number of levels of composites structural organization depends on the content of the silica component. Topological, thermal and relaxation characteristics of the polymers and composites were defined. The effect of small additions takes place in composites of 0,5-1,5 mas. % of silica particles: the high elastic modulus and the internodal chains concentration are increased and the glass transition temperature is decreased. At the concentrations of silica particles higher 1,5 mas. % the topological structure of epoxy matrix is lost: internodal chains concentration and the glass transition temperature are decreased. It was found that epoxy-silica nanocomposites coatings demonstrate the high chemical resistance, maximal impact resistance and provide hight adhesion to the aluminum alloy D16. Composite coatings obtained at room temperature and high temperature curing of epoxy component provide highly efficiency of corrosion protection of the aluminum alloy D16. Application field: Anticorrosion coatings for metal surfaces.