Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Cover Picture (Angew. Chem. Int. Ed. 6/1998)
The cover picture shows a polyethylene chain (white – blue; bottom left) before and after (bottom right) β-alkyl elimination by Ziegler-Natta depolymerization to give oligomers of low molecular weight (the top part shows the forward reaction). The chains are linked to the zirconium atoms (red) of a well-defined (≡SiO)3Zr species on a silica – alumina surface (yellow-orange). The reverse reaction-the insertion of the π-bound olefin unit (the sp2 carbon atoms are shown in magenta) into the Zr-alkyl bond-is the key step in Ziegler-Natta polymerization. More about this interesting zirconium hydride supported on silica -alumina, which also catalyzes the polymerization of ethylene and propylene, is reported by Dufaud and Basset on pages 806–810. The future will show if this catalyst can be used for the recycling of polymers.