Fifty years ago, Karl Ziegler and his co-workers discovered the synthesis of polyethylenes at low pressures and moderate high temperatures with transition-metal catalysts of the 4th group and aluminum organic compounds as cocatalysts. The last 50 years represent a story of innovations in science and industry in the development of high-activity catalysts and processes based on a detailed understanding of all relevant chemical and physical processes on all scales. Catalysts, technologies, and products are still under further development, which shows that the potential of this polymerization process is not fully exploited. Today's targets include achieving better product properties at lower production costs and the substitution of other materials, such as glass, paper, steel, and concrete in certain fields because polyethylenes deliver better resource-saving solutions.

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A d ) Mut(v 4 (1992) No 3 C i ) VCH V e r l u g~g~s e l l~~h u f t mhH, W-6940 W(wherm, 1992 0935-9648/92/0303-0235 $ 3 SO+ 2SjO

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