Metallocene Catalysts

Metallocene catalysts are useful for the polymerization of olefins and copolymerization of ethene or propene with cyclic olefins, styrene, and polar vinyl monomers. These catalysts contain two components such as a metallocene or half‐sandwich complex of transition metals and an organoaluminum compound, methylaluminoxane (MAO), or a perfluorinated boron aromatic compound. Most polymerization active metallocenes contain zirconium or titanium as transition metal but also hafnium, chromium, scandium, or others. The use of metallocene catalysts and their modifications has widely increased the synthetic and technical possibilities in more precisely controlling the polymer composition, polymer structure, tacticity, and other special properties. They allow the synthesis of polyolefins with short‐ or long‐chain branches, different tacticities and stereoregularities, copolymers with high‐compositional uniformity, new norbornene or styrene copolymers, and polyolefin composite materials in a purity that cannot be obtained by Ziegler–Natta catalysts. Today, industries mainly produce metallocene‐based linear low‐density polyethylene (LLDPE) and ethene/propene (EPM and EPDM) copolymers. These polyolefins show a higher growing rate than similar polymers obtained by conventional catalysts. The single‐site character of metallocene/MAO or other metallocene/borate catalysts has led to a better understanding of the mechanism of olefin polymerization.