No abstract

A supported metallocene catalyst was synthesized by sequentially loading methylaluminoxane (MAO) (30 wt % in toluene) and ( n BuCp) 2 ZrCl 2 on partially dehydroxylated silica ES 70 modified by n BuSnCl 3 . Its shock load hydrogen responsiveness was evaluated by polymerizing ethylene for 1 h at 8.5 bar (g) and 758C without separately feeding the MAO cocatalyst. The shock load hydrogen feeding increased the ethylene consumption (at a fairly constant rate), catalyst productivity, as well as the resin bulk density and average particle size at DP (of hydrogen) $3.0 psi. The bulk density increased from 0.25 to 0.31 g/cm 3 . This shows a procedure for overcoming the inherent drop in catalyst productivity caused by heterogenization of metallocenes (that is a method for catalyst activation) and improving the resulting resin bulk density. The volume-weighted mean particle diameter of the resulting polyethylenes was found to be 5.80-11.12-fold that of the catalyst corresponding to DP 5 0.00-7.11 psi, respectively. The resulting kinetic profiles showed to be fairly stable. However, M w and polydispersity index were not affected. The particle size distribution, average particle size, and the scanning electron microscope photographs of the resulting resin particles confirmed the occurrence of the replication phenomenon. On the basis of the above findings, the mechanism of ethylene polymerization under the present experimental conditions has been revisited.

This study investigated the effects of several organotin silica surface modifiers on the ethylene polymerization performance of (nBuCp)2ZrCl2‐based supported catalysts in which MAO and metallocene were sequentially loaded. Each organotin compound acted as a spacer, increasing the catalyst activity. However, the catalyst activity and $\overline M _{\rm w}$ of the resulting polyethylenes varied as follows: Activity and fractional Sn+ charge: nBuSn(OH)2Cl > MeSnCl3 > nBuSnCl3 > Reference catalyst; and, $\overline M _{\rm w}$: Reference catalyst > nBuSnCl3 > MeSnCl3 > nBuSn(OH)2Cl. The above catalyst activity rating was explained considering the influence of the Lewis acidity, that is, the fractional Sn+ charge of the organotin modifiers on the generation, concentration, and electron density at the active [(nBuCp)2ZrMe]+ cation. All the catalysts showed fairly stable kinetic profiles and produced narrow molecular weight distribution resins; 2.8 ≤ PDI ≤ 3.

Propylene was copolymerized with allylanisole (AA) using Me2Si(Ind)2ZrCl2 and Et(Ind)2ZrCl2, and the methylaluminoxane MAO cocatalyst at 70 °C and a cocatalyst to catalyst (Al:Zr) molar ratio of 1 000. It was fed at 8.5 bar(g). The weight‐average molecular weight, $\overline M _{\rm w}$, for both metallocenes decreased as the AA feed concentration increased. Therefore, allylanisole acted as an in situ chain transfer agent. The chain transfer constants, ktr/kp, of AA for Et(Ind)2ZrCl2 and Me2Si(Ind)2ZrCl2 turned out to be 0.33 and 0.40, respectively. The characterization of the resulting products by 1H NMR demonstrated that AA end‐capped the isotactic poly(propylene) chains which showed to be low molecular weight oligomers; 4.96 × 103 ≤ $\overline M _{\rm w}$ ≤ 9.80 × 103. An appropriate chain transfer mechanism for AA has been proposed.