Over 80% of the world’s polyethylene and 99% of its isotatctic polypropylene are made in processes that require supported catalysts. Typically, the catalysts are so active that they disappear into the product and unanchored activators may result in poorer polymer properties. Two decades ago silica-bound activator (SBA) chemistry was identified for anchoring activated metallocenes to silica supports.<br/><br/>Spray-dried porous silicas are used as supports for anchoring silica-bound activators. However, nonporous fumed silica offers an opportunity to examine the chemistry and polymerization behavior of anchored catalysts under conditions that are either more ideal or more extreme compared to supported catalytic chemistry applied to spray dried silica. Thus, we have made catalysts using nonporous fumed silica containing fewer impurities than typical spray dried silica. The fumed silica used has high surface area and an exceptionally small particle size. These properties make the fumed silica capable of carrying a similar range of population of silica-bound activator sites per gram of silica to spray dried silica. Such polymerization appears to offer added insight into the nature of polymer particle growth where initially topologically equivalent anchored active sites become encapsulated, as well as the impact of encapsulation on polymer structure.<br/><br/>We have dehydroxylated the fumed silica at various temperatures from 200 to 700 °C to tune the number of reactive silanol sites without huge loss of surface area.We then applied various parts of the SBA chemistry to these products. The resulting species are characterized using several techniques, including microscopy and solid-state magic-angle spinning (MAS) NMR. The characterization results and comparisons of the fully-formed catalysts using the two silica forms will be presented.

Model, fumed silica-supported catalysts: Characterization and performance

253rd National Meeting (2017)

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