| abstract |
Bridged metallocenes of Group IVb metals provide improved results when the bridge comprises a neutral electron-donor substituent of general formulawhereinR''' is a rigid unsaturated hydrocarbon radical between Z and the bridge, such that Z is separated from the bridge by 2 to 5 carbon atomsZ is nitrogen, phosphorus, oxygen or sulphur,R'''' is H or an alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl having a maximum of 15 carbon atoms, each R'''' being the same or different,j is 1 when Z=O or S and 2 when Z=N or P. |