Polymerization of styrene with tetradentate chelated α-diimine nickel(II) complexes/MAO catalyst systems: Catalytic behavior and microstructure of polystyrene

The recently reported N,N,N,N-tetradentate chelated α-diimine Ni(II) complexes 1–3 were demonstrated to be efficient precatalysts for the polymerization of styrene in the presence of MAO, producing isotactic-enriched heterotactic polystyrenes (isotactic contents in the range 73–75.5%). The corresponding sequence distributions were determined by NMR spectroscopy, and fitted to six probabilistic models of chain propagation. A better conformity to a Bovey–first order Markov chain propagation model was obtained, indicating a chain-end control mechanism. A comparison of the microstructural features with other polystyrenes obtained by several different types of initiation indicates that the polystyrenes are formed by a coordination insertion polymerization mechanism at the nickel centers.