Abstract: Homopolymers, copolymers or block copolymers are prepared by anionic polymerization of acrylates and/or methacrylates in the presence of an initiator composition containing A) an organic alkali metal compound, B) an organic aluminum compound and C) an additive which forms a complex with the alkali metal cation and is selected from the group consisting of open-chain ethers having at least two ether oxygen atoms, macrocyclic ethers and cryptands, or from the group consisting of quaternary cations of the general formula I  where A is N, P, As or Sb and Ra, Rb, Rc and Rd, independently of one another, are each unsubstituted or substituted alkyl, cycloalkyl, aralkyl or aryl, where two neighboring radicals, together with the heteroatom A, may form a 5- or 6-membered heterocyclic structure which may contain one or two further heteroatoms selected from nitrogen, oxygen and sulfur atoms.

Abstract: A catalyst system containing as active constituentsA) metal complexes of the formula I ##STR1## wherein the substituents have the meanings set forth in the specification andB) a compound capable of forming metallocenium ions.

Abstract: In metal complexes of the formula I ##STR1## the substituents have the following meanings: M is a metal of transition group III, IV, V or VI of the Periodic Table of the Elements or a metal of the lanthanide series,Y is a negative leaving atom or a negative leaving group,X and X.sup.1 are negatively charged or uncharged atoms of main group IV, V or VI of the Periodic Table of the Elements,Z is hydrogen, C.sub.1 -C.sub.10 -alkyl, C.sub.3 -C.sub.10 -cycloalkyl, C.sub.1 -C.sub.10 -alkoxy, C.sub.1 -C.sub.10 -alkylthio or dialkylamido having from 1 to 4 carbon atoms in each alkyl radical,R.sup.1 to R.sup.11 are hydrogen, carboorganic or organosilicon radicals,n is 0, 1 or 2 andthe valence of M is 2+n.

Abstract: Polyacrylates based on alkyl acrylates or alkyl alkylacrylates or mixtures thereof as monomers are prepared in the presence of an initiator composition containing an alkali metal ester enolate and an organic aluminum compound or a mixture thereof, by a process in which an ester which differs from the monomers is present in the initiator composition, the carbon atom .alpha. to the ester group having no acidic proton.