The soluble catalyst system methylaluminoxane (MA0)-Ni(acac), (acac: acetylacetonate) gives polystyrene consisting of an amorphous (aPS) and a crystalline isotactic (ips) fraction. Al(CH,),, which is always present in commercial samples of MAO, decreases both polymer yield and stereospecificity. The polymer yield increases with increasing the MAO/Ni ratio but, at the same time, the iPS/aPS ratio decreases. Addition of N(C2H5), (mole ratio N/Ni = 1) increases the proportion of the isotactic fraction, while it decreases the polymer yield. A tentative interpretation of the stereospecificity is reported. Gel permeation chromatography: Mw = 33 -lo3; M, = 18 -1W3. dl Mw = 33 * lo3; M,, = 18lo'. Mw = 110 * lo3; M,, = 53 * 10'. e, M, = 42 -lo3; M,, = 24 -lo3.4

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DADNiX2 nickel–diimine complexes [DAD = 2,6‐iPr2C6H3NC(Me)C(Me)N2,6‐iPr2C6H3] containing nonchelating pseudohalide ligands [X = isothiocyanate (NCS) for complex 1 and isoselenocyanate (NCSe) for complex 2] were synthesized, and the propylene polymerization with these complexes and also with the Br ligand (X = Br for complex 3) activated by methylaluminoxane (MAO) were investigated (systems 1, 2, and 3/MAO). The polypropylenes obtained with systems 1, 2, and 3 were amorphous polymers and had high molecular weights and narrow molecular weight distributions. Catalyst system 1 showed a relatively high activity even at a low Al/Ni ratio and reached the maximum activity at the molar ratio of Al/Ni = 500, unlike system 3. Increases in the reaction temperature and propylene pressure favored an increase in the catalytic activity. The spectra of polypropylenes looked like those of propylene–ethylene copolymers containing syndiotactic propylene and ethylene sequences. At the same temperature and pressure, system 2 presented the highest number of propylene sequences, and system 3 presented the lowest. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 458–466, 2006

The catalyst DADNi(NCS) 2 (DAD ¼ (ArN¼ ¼C(Me)À ÀC(Me)¼ ¼ArN); Ar ¼ 2,6-C 6 H 3 ), activated by methylaluminoxane, was tested in ethylene polymerization at temperatures above 25 8C and variable Al/Ni ratio. The system was shown to be active even at 80 8C and when supported on silica. However, catalyst activity decreased.The catalyst system was also tested in ethylene and 10-undecen-1-ol copolymerization at different ethylene pressures. The best activities were obtained at low polar monomer concentration (0.017 mol/L), using triisopropylaluminum (Al-i-Pr 3 ) to protect the polar monomer. The incorporation of the comonomer increased with the increase of polar monomer concentration. According to 13 C NMR analyses, all the resulting polyethylenes were highly branched and the polar monomer incorporation decreased as ethylene pressure increased. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5199-5208, 2007

This article regards the ethylene polymerization catalyzed by a nickel catalyst and activated by ethylaluminum sesquichloride (EASC). The effects of the reaction conditions [polymerization temperature, cocatalyst (EASC) concentration, and ethylene concentration] on the average molecular weights of the final polymers and reaction yields were evaluated with the help of empirical statistical models. It is shown that reaction temperature and cocatalyst (EASC) concentration exert the most important effects on average molecular weights and catalyst activity. The polydispersities of the obtained polyethylenes are larger than the polydispersities of polyethylenes obtained with typical Brookhart catalysts. The analysis of polymer branching frequencies shows new types of short branching and significant amounts of long branches, which may explain the relatively large polydispersities of the obtained polymer samples. POLYM. ENG. SCI., 50:1797–1808, 2010. © 2010 Society of Plastics Engineers