Silica-supported metallocene/MAO catalysts

In a tour-de-force with respect to the arcane patent literature, Hlatky reviews heterogeneous single-site catalysts. This is complemented by an article by Fink, Steinmetz, Zechlin, Przybyla, and Tesche on the specific subject of propylene polymerization with silica-supported metallocene/MAO catalysts. The mechanistic role of MAO and other activators is then analyzed by Chen and Marks. They define structure-activity relationships that are certain to promote future research and advances. 

Propene Polymerization with Silica-Supported Metallocene/MAO Catalysts... 

Figure 1. Parameters which influence polymerization kinetics, polymer structure, polymer morphology, and the fragmentation process of a silica-supported metallocene/MAO catalyst during olefin polymerization.

Figure 10. Propene polymerization profiles of a silica-supported metallocene/MAO catalyst prepared by suspension impregnation (a) depending on polymerization time and polymerization temperature and (b) depending on particle size and polymerization time, (c) Comparison of the activity profiles between an 1-octene prepolymerized catalyst and an untreated system, (d) Comparison of the activity profiles between a catalyst system employing 2 vol % hydrogen and the not activated system.

Fig. 23 Propylene polymerization with a silica-supported metallocene/MAO catalyst, (a) Plot of polymerization rate against time. Electron microscope images of particles at stages of (b) prepolymerization, (c, d) particle fragmentation, and (e) particle expansion. See text fm details...

Figure 9. (a) TEM micrograph of a supported metallocene/ MAO catalyst particle prepared by gas-phase Impregnation with TMA/H2O. (b) EDX line scan analysis of the metal-locene/MAO-supported silica gel regarding the silicon and aluminum distribution in the volume. Under this condition, the active sites are formed on the outer surface of the particle. The mean particle size shifted from 50 /rm for the silica support to 70 /nm for the catalyst. 

At Al/Zr = 200, a variety of metallocene—MAO catalysts were supported on silicas dried at various temperatures (Table 2). Supports dried at lower temperatures afforded catalysts of higher activities pretreating the support with AlMes also diminished activity. Analysis of the distribution of aluminum and silicon indicates a very even distribution of cocatalyst on the support, with no more catalyst on the outer surface than within the pores. ... 

Furthermore, the solvent used in many leaching experiments has been toluene, in which many metallocene—MAO catalysts have some solubility, especially at high Al/M ratios. However, to the best of the author s knowledge, few if any commercial polymerization processes use toluene as a diluent. Aliphatic hydrocarbons, bulk monomers, and fluidizing gas streams are used in large-scale plants. Especially at the lower excess of aluminum used in many supported catalysts (50—200 1), metallocene— MAO catalysts are insoluble in hydrocarbon solvents. The heptane extracts from a Cp2ZrCl2—MAO catalyst supported on silica showed no activity in ethylene polymerization, even when additional MAO was added. 

Porous acrylonitrile—DVB copolymer further reacted with diamines or triamines provides a support for Cp 2ZrCl2—MAO catalysts.2 2 pjjg catalyst activity rivals that of silica-supported analogues and no adhesion of polymer to the reactor walls or stirrer was observed. Polypropylene grafted with maleic anhydride allowed to react with MAO acts as a support for a variety of metallocenes. 3 The number of gels in the polymer is lower than when silica is used as the carrier. Porous vinylpyridine—DVB and poly(vinyl chloride) have also been reported as suitable support materials for metallocene catalysts. 

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