High activity magnesium chloride supported catalysts for olefin polymerization. XXIX. Molecular basis of hydrogen activation of magnesium chloride supported Ziegler–Natta catalysts

Abstract

Abstract Hydrogen ( p H 2 = 72 torr) increases the rate of propylene polymerization by a MgCl 2 /ethyl benzoate/ p ‐cresol/AlEt 3 /TiCl 4 ‐AlEt 3 /methyl‐ p ‐toluate catalyst (CW‐catalyst) by two‐to three‐fold which corresponds closely with the increase in the number of active sites as counted by radiolabeling with tritiated methanol. The oxidation states of titanium in decene polymerizations by the CW‐catalyst were determined as a function of time of polymerization ( t p ). In the absence of H 2 , all [Ti +n ] for n = 2, 3, 4 remain constant during a batch polymerization. In the presence of H 2 and within 5 min of t p , [Ti +2 ] decreases by an amount, corresponding to 15% of the total titanium and [Ti +3 ] increases by the same amount, while [Ti +4 ] is not changed. Therefore, three‐fourths of the H 2 activation result from oxidative addition processes. The remaining one‐fourth of the H 2 activation may be attributed to the activation of previously deactivated Ti +3 ions by hydrogenolysis. Monomer converts some of the EPR silent Ti +3 sites to EPR observable species resulting in their activation.