Kinetic study on olefin polymerization with heterogeneous titanium catalysts

The effect of two different cocatalysts (Al(C2H5)(3) and methyl aluminoxane (MAO)), on two different titanium catalysts (TiCl3. 1/3AlCl(3) and TiCl4/EB/MgCl2) has been investigated for propylene polymerization and ethylene-propylene copolymerization. For propylene polymerization, MAO showed higher catalytic activity and stereospecificity than Al(C2H5)(3). From short-time polymerization kinetics, MAO increased the propagataion constant (k(p)) for both catalytic systems. For ethylene-propylene copolymerization, when MAO was used as a cocatalyst, higher catalytic activity and propylene composition at the same feed composition were found.C- 13 NMR spectroscopy and DSC showed the microstructure of ethylene-propylene copolymers depended strongly upon the types of cocatalyst. In spite of higher propylene composition, the ethylene-propylene copolymers obtained by MAO showed higher crystallinity than those obtained by Al(C2H5)(3). From C-13 NMR, this might be due to the propylene configuration in the copolymer. This observation might be attributed to the different interaction between catalytic titanium sites and cocatalysts, especially the electron donor effect of MAO to Lewis acidic titanium sites. (C) 1998 Elsevier Science Ltd. All rights reserved.