dThe development of an isospecific styrene polymerization catalysts system based on methylaluminoxane (MAO)-activated group 4 metal non-metallocene complexes is reported. The ligand derived from the 1,4-dithiabutanediyl-linked bis(phenol)s has been designed in order to ensure stereochemical rigidity utilizing the potentially hemi-labile function of the sulfur donors. Isospecificity during styrene polymerization was achieved using easily accessible catalyst precursors of the type [MX2(OC6H2-'Bu-2-4, 6)(2) {S(CH2)(2)S}] (M = Ti, Zr, Hf; X = Cl, CH2Ph). A remarkable dependence of both the activity and stereoselectivity on the ligand backbone was observed, as analogous precursors with 1,5-dithiapentanediyl-linked bis(phenolato) ligand gave syndiotactic polystyrene with lower activity. (C) 2003 Elsevier B.V. All rights reserved.