Cocatalysts polymerization test results

An example of this increase in LCB is shown in Figure 177. H3PO4 was added to Cr/alumina catalyst in varying amounts prior to activation at 650 °C, and then these catalysts were tested for ethylene polymerization activity. The LCB contents of the resultant polymers, as measured by the JC method, are plotted against the amount of phosphate added to the catalyst. Three series of polymerization runs were made. In the first series, the catalyst contained no sulfate, and BEt3 cocatalyst was used with H2 in the reactor. The LCB level in the polymer was found to increase by almost two orders of magnitude as phosphate was added to the catalyst. 

Some examples of the influence of solid cocatalysts are shown in Table 58. A Cr/silica catalyst, activated at 800 °C, was tested in ethylene polymerization experiments in the presence of various solid adsorbents. In control polymerization runs, with only the catalyst and no cocatalyst, it was difficult to obtain measurable activity data when less than about 0.10 g of catalyst was added to the reactor. This result is a sign that even with the most diligent attention to feedstock purity, there is always a low level of background poison, which means that a threshold amount of catalyst is needed in the reactor to achieve measurable activity. 

An example illustrating this behavior is shown in Table 62 Cr(VI) and Cr(II) catalysts, otherwise identical in composition, were tested for ethylene polymerization in the absence and presence of BEt3 cocatalyst. The second column in the table shows the degree of branching found in the resultant polymer, and the third column shows the density of that polymer. The response by Cr(VI) to the cocatalyst was only slight, but the response by Cr(II) was remarkable. With the addition of BEt3, the density of the polymer dropped so severely that the product type changed from the class of HDPE (homopolymer) to LLDPE. 

The initial temperature of catalyst activation can also influence the amount of in situ branching obtained in the polymer. This is in agreement with the olefin-generating behavior of the organochromium catalysts (Figures 185 and 192, Table 55). Table 67 shows an experiment in which Cr/silica-titania was activated at 800 °C or at 650 °C, and then it was reduced and tested for polymerization activity with 5 ppm triethylboron cocatalyst. The 800 °C catalyst resulted in significantly lower polymer density than the 650 °C catalyst. This derives from two causes. The 800 °C... 

We disclosed a few years ago that borohydride derivatives of the rare earths can advantageously be used as precatalysts for the polymerization of nonpolar monomers, in combination with metal-alkyl compounds as cocatalysts [12], Such catalysts were found to be very versatile as various monomers were successfully tested. Magnesium cocatalysts gave rise to controlled polymerizations, and the results were different depending on the precatalyst/cocatalyst ratio. Aluminum cocatalysts required the addition of a borate activator to afford polymers. Other catalytic combinations starting from phenate and MOF (metal organic framework) derivatives of the rare earths were also assessed and compared with the borohydride-based ones. 

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