Comparison of the generation II with IV heterogeneous Ziegler-Natta catalysts used in propylene polymerizations

An unsupported TiCl3-based catalyst (generation II), modified with n-butyl ether and AlEt2Cl3, was compared with a MgCl2/dibutyl phthalate/AlEt3/cyclohexylmethyldimethoxysilane catalyst system (generation IV) in propylene polymerizations. The latter (magnesium-supported) was found to be more than 20 times as active as the former and more stereospecific, but to yield PP with a lower molecular weight (Table 2). The kinetics of the polymerizations studied with either of the catalyst, and involving the determination of concentrations of active sites [C-o*] and elementary reaction rate constants (Table 4) based on earlier kinetic models, showed the C-o*-values in the magnesium-supported catalyst to be much higher than those in the unsupported catalyst, thereby bearing out the higher activity of the former, whereas the propagation rate (k(rp)) remained practically unaffected.