ON THE CATALYSIS OF STEREOSPECIFIC POLYME RIZATION OF BUTADIENE WITH THE CATALYST SYSTEMS FROM ND(ETA(3)-C3H5)(3)CENTER-DOT-DIOXANE AND METHYLALUMINOXANE AS WELL AS HEXAISOBUTYLALUMINOXANE

The activation of the tris(allyl)neodymium complex Nd(eta(3)-C3H5)(3) . dioxane with alkylaluminoxanes (MAO or HIBAO) results in highly sele ctive catalysts for the 1,4-cis-polymerization of butadiene (cis-selec tivity up to 80%). Under standard conditions (50 degrees C, toluene), the turnover frequency (TOF) of the catalyst/MAO system amounts to 10- 15000 mol butadiene/(mol Nd . h). Molecular weight determinations indi cate the formation of only one polymer chain per neodymium center as i n a living polymerization reaction, and for the catalyst/HIBAO system the rate law r(p) = k(p)[Nd][C4H6] with k(p) = 8,7.10(-2) mol/(L . s) (at 25 degrees C) has been derived. As the catalytically active specie s, a cationic monobutenyl neodymium(III) complex is discussed, which i s stabilized through coordinative interaction with the counter anion a s well as the growing polybutadiene chain. This cationic complex react s under insertion with butadiene in a bimolecular fashion.