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 10(6) 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.