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did not affect the solid-state electronic environment. However, it increased the surface cocatalyst to catalyst molar ratio (Al : Zr), acted as a spacer, increased catalyst activity, and enhanced chain-transfer reactions. The separately fed MAO cocatalyst shifted the equilibrium between Cation 1 and Cation 2 toward the right. Consequently, more Cation 2 was generated, which acted as the effective and active single-site catalytic species producing monomodal PDI.

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.

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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.

The impact of common process catalyst poisons on the performance of a 6th generation Ziegler–Natta catalysts during the gas phase polymerization of propylene are examined using two approaches: introducing propylene without purification, or with one or two sets of purification columns, and by introducing carbon dioxide (CO2), oxygen (O2), water (H2O), methanol (CH3OH), ethyl acetate (C4H8O2) and dimethyl sulfoxide (C2H6SO) during the polymerization. As expected, purification columns increases the catalyst activity significantly, slightly reduce catalyst decay. Injecting TiBA during the reaction leads to an activity increase. The addition of two full sets of columns substantially increased the repeatability of polymerization reactions. The power of deactivation of poisons injected during the polymerization reaction is: O2 > CO2 > CH3OH > C2H6SO > C4H8O2 > H2O. Adding CO2, O2, and CH3OH resulted in a progressive decrease in molecular weight while almost no effect is observed with H2O. However, C4H8O2, and C2H6SO resulted in a mild increase in molecular weight. Additionally, the effects on crystallinity and stereoregularity are similar where CO2, O2, H2O and CH3OH caused a progressive decrease while C4H8O2 and C2H6SO resulted in a mild increase, indicating some isotacticity control by these two poisons.

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