Kinetic Modeling of Slurry Propylene Polymerization using rac-Et(Ind)2 ZrCl2/MAO.

The slurry homopolymerization of propylene catalyzed by the isospecific metallocene rac-Et(Ind)₂ZrCl₂/MAO was investigated using a semi-batch reactor. A full factorial design with three temperatures (50, 65 and 75°C) and four monomer partial pressures (1.5, 2.5, 3.2, and 3.8 atm) was performed. Analysis by ¹H NMR revealed the formation of vinylidene, cis-2-butenyl and 4-butenyl end-groups. A kinetic model based on a coordination-insertion mechanism was developed to predict instantaneous reaction rate, molecular weights and polymer chain ends. The kinetic rate constants were estimated using a systematic optimization strategy. The model predicts that the insertion of the first propylene molecule is rate limiting with respect to propagation. Molecular weight decreases with temperature due to the high activation energy of the main chain transfer reaction (101 kJ/mol) relative to propagation (52 kJ/mol). The percentage of butenyl end-groups with respect to vinylidene decreases with temperature, thus predicting a lower activation energy for the β-hydride elimination after secondary insertion (27 kJ/mol). [ABSTRACT FROM AUTHOR]