Polymerization of Styrene Versus Propylene with MgCl₂-Supported Catalysts

Abstract

It is well known that MgCl₂-supported TiC1₄ (MgC1₂/TiC1₄) catalyst in combination with A1Et₃ shows much higher activity in propylene polymerization than the conventional TiC1₃ catalyst system,¹ but the stereospecificity of the obtained polymer is rather low, namely 20–40% as isotactic index (I.I.). In a study of kinetics on short time polymerization,² it was concluded that a cause of the low stereospecificity of this catalyst system was due to the high concentration of atactic active centers ([C*]ata = 14–58%). We also reported that a catalyst system composed of MgC1₂/TiC1₄/ethyl benzoate- A1Et₃/ethyl benzoate showed very high stereospecificity in both propylene and styrene polymerization and the concentration of the isotactic active centers in both polymerizations was similar,^3,4 ([C*]_iso(PP)) = 1.3%, [C*]_iso(St) = 3%, suggesting comparable isotactic active centers for both monomers.