CoachA Ziegler–Natta catalyst polymerises alkenes at low pressure; it is made from a transition-metal halide, typically of titanium, and an alkylaluminium compound. The Cossee–Arlman mechanism of chain growth is the coordination of the alkene at a vacant site cis to the growing alkyl chain on the metal, followed by its migratory insertion into the metal–carbon bond, which leaves a vacant site again. A single-site catalyst has all its active centres identical, as in a molecular metallocene catalyst.
