Polymerization of styrene using catalytic systems based on nickel derivatives and methylaluminoxane (MAO) was studied. Among tested catalysts, nickel bis(acetylacetonate) and nickel dichloride show the maximum activity. Bis(phosphine)nickel dichlorides exhibit lower activity, depending on the nature of the phosphine ligand. Polymer yields decrease by lowering the catalyst concentration, by increasing the reaction temperature, or by carrying out the polymerization in a polar donor solvent. Weight average molecular weight of most of the prepared polystyrenes ranges from 9000 to 25,000, with polydispersity indexes of 1.6–3.8. However, polystyrene prepared in dioxane solvent exhibits a small fraction of very high molecular weight (about 140,000). From NMR analysis, the products seem generally to be constituted of two polymers with different steric microstructure: atactic polystyrene and partially isotactic polystyrene (ca. 75–85% meso diads). Catalytic site specificity is correlated with the type of nickel ligand, while the effect of reaction temperature is less defined. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2119–2126, 1998

SYNOPSIS2,2'-Bis (2-oxazoline) was used as a chain extender during processing in a twin-screw extruder with the aim of counteracting degradation phenomena in recycled poly (ethylene terephthalate) (PET). The same experiments were performed on fiber-grade PET for comparison purposes. Rheological characterization showed that while the melt viscosity of fiber-grade PET at constant temperature and shear rate is quite constant with time, that of recycled P E T decreases dramatically. By addition of oxazoline, an increase of melt viscosity occurs for fiber-grade PET, whereas for recycled PET, thermal and hydrolitic degradation effects are partially compensated. Characterization was performed by solution viscosity measurements, gel permeation chromatography, and COOH end-group titration on samples obtained a t variable residence times at 280°C. Lower molecular weights accompanied by a higher amount of COOH were observed; the use of oxazoline resulted in higher molecular weights and lower COOH concentrations at equal residence times, while polydispersity did not vary. 0 1993 John Wiley & Sons, Inc.

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