Zirconocene catalyst with boron cocatalyst for methyl methacrylate polymerization

Abstract

Zirconocene catalyst, rac-Et(Ind)2ZrCl2 was alkylated with Grignard reagent, then combined with a boron cocatalyst: B(C6F5)3, Ph3C+B(C6F5)4- or PhNMe2H+B(C6F5)4-. To perform the polymerization of methyl methacrylate monomer, Zn(C2H5)2 which is a Lewis acid, was used to complex with methyl methacrylate before adding the catalyst to the reaction in order to protect the zirconocene catalyst from being poisoned with a polar functional group of the monomer. The role of Lewis acid presumably involved in the initiation step of polymerization. The reaction can be carried out over a range of polymerization temperature from -78 degree celcius to 30 degree celcius. The polymer obtained was isotactic poly(methyl methacrylate) (PMMA) with high molecular weight, revealed from NMR spectrum and GPC measurement. In addition, the glass transition temperature of the polymer from DSC measurement was around 50 degree celcius. The catalytic activity increases with an increase of catalyst concentration. The polymer yield increases with polymerization time, which indicates that the propagation rate is independent on monomer concentration. The optimum mole ratio of MMA/Zn is 4. In this study, the narrow molecular weight distribution, a characteristic demonstrated by metallocene catalyst is also shown (Mw/Mn<2.5).