The success of in situ polymerizations, measured by means of high polymerization activity, uniform exfoliation and clay dispersion in the polymer matrix, and good powder morphology, depends on how well the catalyst is supported onto the clay surface. A novel catalyst supporting method that does not require the addition of methylaluminoxane was applied to different organically modified clays and sodium montmorillonite. The supported catalysts were used to polymerize ethylene. We found out that only the clay modified with tertiary ammonium salts was an effective support for ethylene polymerization, generating a supported catalyst that has high polymerization activity, and produces nanocomposites with good powder morphology and excellent clay exfoliation. magnified image
Polyolefin‐clay nanocomposites are finding many new applications because of their improved properties, such as high modulus, elevated scratch resistance and low gas permeability. Currently, these composites are produced by melt blending organically modified clay with polyolefins. The most challenging step in this process is the intercalation and exfoliation of the clay to produce a homogenously dispersed phase at the nanoscale. A promising alternative to melt blending is in‐situ polymerization, where the polymer is produced between the clay layers in the polymerization reactor. In‐situ polymerization of olefins with metallocene catalysts supported on clay can produce nanocomposites using conventional polymerization reactors, provided that the clay can be used as a support for the olefin polymerization catalyst. In this approach, the clay fulfills the functions of catalyst support and dispersed phase in the final nanocomposite. In this work, a mathematical model describing particle growth during in‐situ polymerization of ethylene with a metallocene catalyst supported on clay will be discussed. The model expands the approach of the multi‐grain model used in heterogeneous olefin polymerization to account for the layered structure of clays.
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