Particulate group 4 metallocene-aluminoxane catalyst compositions devoid of preformed support, and their preparation and their use

#This invention relates to novel, highly effective solid aluminoxane/metallocene olefin polymerization catalysts, their preparation, and their use.

#Hydrocarbylaluminoxanes (also known as alumoxanes) complexed with transition metal compounds, such as metallocenes, have been found to be effective olefin polymerization catalysts. Methylaluminoxanes are especially effective catalyst components in forming homogeneous catalyst systems with various metallocenes. However, these catalyst systems have proven to be considerably less effective in productivity per unit weight of catalyst when used as supported heterogeneous catalysts, either in the form of dispersions in a liquid medium or as supported solid catalysts in gas-phase polymerizations. For example, in U.S. Pat. No. 5,126,301 issued Jun. 30, 1992 to Tsutsui et al. it is pointed out that when an olefin is polymerized or copolymerized in a dispersion or gas-phase polymerization system by utilizing carrier-supported metallocene-aluminoxane catalysts, polymerization activity is markedly reduced, that the properties inherent to the catalyst comprising the transition metal compound and the aluminoxane catalyst component are not fully exerted, and that powder properties such as bulk density of the thus prepared polymer were insufficient. The approach taken by Tsutsui et al. was to form a solid catalyst by contacting an a-olefin with a mixture obtained by mixing an organoaluminum compound having a branched alkyl radical, an aluminoxane of specified aluminum content, a fine-particle carrier, and a transition metal metallocene compound.

#Despite various improvements made during the course of extensive research activities by various laboratories, a need has existed for olefin polymerization catalysts having even better performance characteristics. For example, U.S. Pat. No. 5,498,581 issued Mar. 12, 1996 to Welch et al., points out that evaluation of attempts disclosed in U. S. Pat. Nos. 5,240,894; 4,871,705; and 5,106,804 to overcome the disadvantages of metallocene catalysts has revealed that there is still room for improvement, particularly when the catalyst is one which is to be used in a slurry-type polymerizations. The techniques disclosed in U.S. Pat. Nos. 5,240,894; 4,871,705; and 5,106,804 involve prepolymerization of the metallocene-aluminoxane catalyst system either in the presence or absence of a support.

#A metallocene/methylaluminoxane solution was prepared by adding the olefinic substituted zirconocene (0.00166 mole Zr) to 71.2 grams of 30 wt % methylaluminoxane (MAO) in toluene solution (13.2% Al). The mixture was diluted with 129.2 grams of toluene and then stirred at 25° C. for about 0.5 hour. The metallocene/MAO solution was charged to the reactor. The volume of the contents of the reactor was adjusted to 0.42 liter with addition of toluene. The mixture was cooled to 15° C. The reactor was pressure/vented with ethylene to about 20 psig three to four times to remove nitrogen. The ethylene pressure was adjusted to 5 psig. The prepolymerization of the metallocene/MAO was started. A total of about 33 to 34 grams of ethylene was charged into the reactor over 155 minutes at 15° C./5 psig. The reactor was pressure/vented with nitrogen several times to remove ethylene. The mixture was warmed to 20° C. The contents of the flask were transferred to a nitrogen filled bottle. The bottle was then placed into a dry box. The mixture was filtered through a 600 mL coarse sintered glass frit. The catalyst was washed once with about 300 mL of toluene and once with 300 mL of isopentane. The catalyst was transferred to a one liter flask and was dried under vacuum for 12 hours. Yield of solid catalyst was 32 grams. The surface area of the catalyst particles was 3.64 square meters per gram. When ethylene was polymerized using the above procedure for determining productivity, it was found that the productivity of this heterogeneous catalyst was 23,967 g PE/g catalyst.

#Example 1 was repeated in the same manner except that 18 g of ethylene was used in the prepolymerization step instead of 33 to 34 grams, the prepolymerization reaction was conducted for 85 minutes, and 19 grams of the solid catalyst of the invention was isolated. The surface area of this particulate catalyst was 6.90 square meters per gram. The productivity of this catalyst using the above procedure was 31,000 g PE/g catalyst.

#Example 1 was again repeated with the exception that the amount of ethylene used in the prepolymerization was 46.8 grams, the prepolymerization was performed for 320 minutes, and the amount of isolated solid catalyst of this invention was 47 grams. The surface area of this solid catalyst was 2.57 square meters per gram. The productivity of this catalyst using the above procedure was 18,300 g PE/g catalyst.