Magnesium chloride supported high‐mileage catalysts for olefin polymerization. X. Effect of hydrogen and catalytic site deactivation

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Abstract
The effect of H2on propylene polymerization initiated by a MgCl2/EB/PC/AlEt3/TiCl4–3 AlEt3/MPT catalyst was studied. Hydrogen increases significantly the initial rate during the early stage of the polymerization to give a higher yield of polymer than reactions without H2. But H2reduces the yield toward the latter stages so that the net effect on the total yield can be quite small. There is no appreciable effect of H2on either the isotacticity index or polydispersity of the products. It decreases molecular weight proportional to (pH2)1/2. The chain transfer by H2resulted in a decrease of total metal polymer bond concentration with time of polymerization. The rate constants of hydrogen chain transfer for the two kinds of isospecific and nonspecific sites are= 5.1 × 10−3,= 2.7 × 10−3,= 7.5 × 10−3,= 4.4 × 10−3, in units of torr1/2sec−1at 50°. Hydrogen assists in the deactivation of the catalytic sites as does propylene; rates of the former and the latter vary with (pH2)1/2and [C3H6]1/2, respectively, withk= (12.1 ± 0.9) M−1torr−1/2sec−1andk= (65.3 ± 3.3) M−3/2sec−1at 50° andA/T= 167. The mechanism for deactivation of catalytic sites are discussed.
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