Metallocene Catalyzed Polymerization of Methylmethacrylate

Abstract

Metallocenes are organometallic compounds consisting of two cyclopentadieny ligands and a transition metal, such as ferrocene [1]. One of the most important properties of metallocenes is their catalytic activity for olefin polymerizations [2]. Breslow et al. and Natta et al. [3] first reported the polymerization of ethylene using dicyclopentadienyltitanium dichloride (Cp₂TiCl₂) activated by an aluminum alkyl, such as diethylaluminum chloride in 1957. However, the activities of this polymerization system were very low, and were not effective for propylene. In 1980, Shinn et al. [4] discovered that dicyclopentadienylzirconium dichloride (Cp₂ZrCl₂) activated by methylaluminoxane (MAO), which are condensed products from trimethylaluminum and water, showed extremely high activity for ethylene polymerizations. Since their discovery, metallocenes with MAO systems for olefin polymerizations have been investigated vigorously and great progress has been achieved in this field. In the 1980s, research on metallocene polymerizations was focused on stereospecific polymerization of 1-olefins (mainly propylene). In 1984, Ewen [5] reported that a mixture of meso- and rac-isomers of ethylenebis(indenyl)-titanium dichloride (EtInd₂TiCl₂) upon activation with MAO affords a mixture of isotactic and atactic polypropylene. Kaminsky et al. [6] reported the first example of isospecific polymerization of propylene by C ₂-symmetrical rac-ethylenebis(indenyl)zirconium dichloride (rac-EtInd₂ZrC1₂) as precatalyst in 1985. A syndiotactic polypropylene was reported by Ewen et al. [7]. They used the C _s-symmetrical dimethylmethylenecyclopenta-dienyl fluorenylzirconium dichloride (Me₂CCpF1uZrCl₂) as precatalyst.