Group 4 metallocene polymerisation catalysts: quantification of ring substituent steric effects

This review summarises attempts that have been made to quantify and separate steric and electronic factors associated with zirconocene-type catalysts in the olefin polymerisation reaction. The use of cone and solid angles, measurement of molecular spaces (coordination gap aperture, obliquity angle and lateral extension angle), the Taft steric parameter as well as a number of theoretical methods (ab initio Hartree Fock, QSAR, 3D-QSAR and paired interacting orbitals) as approaches to the quantification of ligand size is discussed. Attempts to associate these measures with catalyst activity are reviewed.