Polymerization of α-Olefins with a Supported Ziegler-type Catalysts. I. Influence of Various Supports on the Polymerization Rate and the Tacticity of Polypropylene.

Abstract

The influence of the support on both the polymerization rate and the tacticity of polypropylene has been widely investigated by using various supported Ziegler-type catalysts. The supports used were metal chloride hydroxide of Mn, Co, Ni, Ba, Cd, Fe, Mg, Sr, etc., magnesium hydroxide, silica gel, and some organic polymers such as poly(ethylene glycol), poly(vinyl sulfonic acid) (K-salt) and sodium polyaerylate.The supported catalysts were prepared by allowing the supporting compounds to react with titanium tetrachloride (TiCl4) in boiling n-heptane. Polymerizations were carried out in n-heptane at 50°C with the use of triethylaluminum as an activator. Although the polymerization rate with carrier-free TiCl4 decreased remarkably with the polymerization time, that with supported TiCl4 remains constant during the course of polymerization over several hours. Magnesium hydroxide and magnesium chloride hydroxide-supported catalysts showed the highest activity among the supports.As for the tacticity, on the other hand, a sharply peaked relationship with a maximum value near 0.70 A has been found between the tacticity of the produced polypropylene and the ionic radii of the metals used as supports.The apparent activation energy of the polymerization with magnesium chloride hydroxide-supported TiCl4 catalyst was estimated to be 5.5 kcal/mole in the temperature range between 20°C and 70°C. This value is equal to that of carrier-free TiCl4 catalyst at a lower temperature range.