POLYMERIZATION OF STYRENE WITH NICKEL-COMPLEX METHYLALUMINOXANE CATALYTIC-SYSTEMS

Polymerization of styrene using catalytic systems based on nickel deri vatives and methylaluminoxane (MAO) was studied. Among tested catalyst s, nickel bis(acetylacetonate) and nickel dichloride show the maximum activity. Bis(phosphine)nickel dichlorides exhibit lower activity, dep ending on the nature of the phosphine ligand. Polymer yields decrease by lowering the catalyst concentration, by increasing the reaction tem perature, or by carrying out the polymerization in a polar donor solve nt. Weight average molecular weight of most of the prepared polystyren es ranges from 9000 to 25,000, with polydispersity indexes of 1.6-3.8. However, polystyrene prepared in dioxane solvent exhibits a small fra ction of very high molecular weight (about 140,000). From NMR analysis , the products seem generally to be constituted of two polymers with d ifferent steric microstructure: atactic polystyrene and partially isot actic polystyrene (ca. 75-85% mesa diads). Catalytic site specificity is correlated with the type of nickel ligand, while the effect of reac tion temperature is less defined. (C) 1998 John Wiley & Sons, Inc.