Mechanism of metallocene catalysts

Mechanism of metallocene catalysts requires a co catalyst for activation. One of the most common co catalysts for this purpose is Methylalmuinoxane (MOA). Other catalysts include, Al(C2H5)3. There are numerous metallocene catalysts that can be used for propylene polymerization. Some metallocene catalysts are used for industrial process, while others are not, due to their high cost. One of simplest is Cp2ZrCl. Different catalyst can lead to polymers with different molecular weights and properties. Active research is still being conducted on metallocene catalyst. In the mechanism the metallocene catalyst first reacts with the co catalyst. If Metylalmuinoxane (MAO) is the co catalyst, the first step is to replace one of the Cl atoms on the catalyst with a methyl group from the Metylalmuinoxane (MAO). The methyl group on the MAO is replaced by the Cl from the catalyst. The MAO then removes another Cl from the catalyst. This makes the catalyst positively charged and susceptible to attack from propylene. Once the catalyst is activated, the double bond on the propylene coordinates with the metal of the catalyst. The methyl group on the catalyst then migrates to the propene, and the double bond is broken. This starts the polymerization. Once the methyl migrates the positively charged catalyst is reformed and another propene can coordinate to the metal. The second propene coordinates and the carbon chain that was formed migrates to the propene. The process of coordination and migration continues and a polymer chain is grown off of the metallocene catalyst.