Within the last 2 decades a large number of metallocene/MAO copolymerization catalysts has been developed, targeting tailor-made high-quality ethylene−propylene elastomers. However, under the widely used EP(D)M solution polymerization process temperatures, conventional metallocene catalysts give only access to the lower 15% of the commercial molecular weight range, established with Ziegler−Natta catalysts, which extends to about 106 g/mol. The novel class of donor−acceptor metallocenes makes a quantum leap in enhancing in EP(D)M molecular weights by orders of magnitude. Thus, the full molecular weight range of tailor-made polyolefin elastomers up to ultra high molecular weights is now accessible. At lower temperatures the D−A metallocene catalyst systems approach 100% chain growth selectivity in living olefin homo- and copolymerizations.

D/A metallocenes constitute a novel unique class of catalysts, in that they are able to express structural information within the elementary steps of the catalytic cycle out of bridged as well as out of unbridged states due to the coexistence of donor (D) and acceptor (A) atoms in complex sandwich structures. Highly polarized transannular bridging interactions as well as Lewis basic and Lewis acidic functionalities in unbridged states are the prerequisites which define a modular highly flexible catalyst system with outstanding options to tailor materials and processes.

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