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In the present work, the interaction forces between paraffin surfaces and solid substrates were studied using an atomic force microscope (AFM). Approximation and retraction curves, called force curves, were measured at room temperature between the AFM probe and stainless-steel (SS) substrates with either of them uncoated or coated with a paraffin film. A great influence of the surface topography on the force curves was observed. This influence results in a large variation of the interaction force values obtained at different spots of the sample surface. For some of the spots, which are associated with large paraffin crystals or agglomerates, the force curves change each time a measurement is performed, apparently because of the deformation of the paraffin crystal. For some other spots, which seem to be related to thin paraffin layers, a reproducible behavior is observed, allowing for the estimation of the interaction force values. A considerable dispersion of the values of adhesion forces and jump-in and ...

The force curves between an AFM probe and paraffin films deposited by casting of paraffin solutions in heptane onto crystalline silicon substrates were studied. The results show that paraffin deposits undergo a permanent deformation when the first force curve is performed not recovering its original situation. When subsequent force curves are performed at the same location, the force curves present a reproducible behavior. Gradual response of retraction curves indicate that an interaction of viscous adhesion occurs during jump-out of the AFM probe. In case of measurements performed many hours after the deposition of the films, the jump-in and jump-out distances are situated around 310 and 420 nm, respectively; while adhesion forces values are around 60 nN in the case of the first contact between the AFM probe and paraffin film and 40 nN for the subsequent contacts. Force curves results obtained for different times after deposition of the layers show that the interaction between the AFM probe and paraffin films is dependent on elapsed time. Fresh films appear to be damp and sticky, changing their properties as the solvent is evaporated. Adhesion force and pull-off distance decrease as a function of time up to about 30 min and then for longer times decrease at a much smaller rate. The separation energy between the tip and paraffin films is large just after paraffin deposition, decreasing abruptly with time and reducing very slowly after 15 min.

DADNiX2 nickel–diimine complexes [DAD = 2,6-iPr2C6H3NC(Me)C(Me)N2,6-iPr2C6H3] 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

Three isothiocyanate complexes of nickel(II) containing diimine [ArNC(Me)C(Me)NAr]Ni- (NCS)2 (1), iminophosphine [Ph2PC6H4CHNAr]Ni(NCS)2 (2), or diphosphine (dppe)Ni(NCS)2 (3), [Ar = 2, 6-iPr-C6H3; dppe = 1, 2-bis(diphenylphosphine)ethane] were synthesized and examined for ethylene polymerization activated by methylaluminoxane (MAO). Their behavior was compared with those of the corresponding halide analogues [ArNC(Me)C(Me)NAr]NiBr2 (4), [Ph2PC6H4CHNAr]NiBr2 (5), and (dppe)NiCl2 (6). The diimines showed the highest polymerization activity. Replacement of the halide for the NCS pseudo halide affected the activity and decreased the molecular weight of the polymer formed. The highest molecular weights were obtained with the diimine complexes. Highly branched polyethylenes were obtained with the bulkier complexes 1 and 4. Replacement of the halide for NCS in the diimine complexes also caused an increase in the branching content, whereas the opposite occurs for the iminophosphine complexes. The different activities and behavior of the catalyst systems with halide versus NCS in the polymerization of ethylene and the characteristics of the final products suggest a modification in the active species caused by the non-chelating ligand. Polymer molecular weight and branching content is dependent on the MAO/Ni molar ratio and on the working temperature. Copyright © 2004 John Wiley & Sons, Ltd.

A complete 13C NMR characterization of a polymer synthesized with a new Ni-diimine complex [DADNi(NCS)2, where DAD = 2,6-iPrC6H3NC(Me)C(Me) N2,6-iPrC6H3] activated by methylaluminoxane by homopolymerization of propylene is presented. The amorphous material was made up mainly of blocks of syndiotactic polypropylene and ethylene–propylene copolymer. Some degree of propylene inversion (

In the title compound, [NiBr(2)(C(31)H(32)NP)], (I), the second reported example of a nickel-iminophosphine N,P-chelate in which the Ni atom has tetrahedral coordination, the Ni coordination is distorted as a consequence of the N-Ni-P chelate bite angle of 91.07 (6) degrees compensated by the Br-Ni-Br angle of 126.385 (18) degrees. In (I) and its analogue, viz. dichloro[[2-(4-isobutyloxazol-2-yl)phenyl]diphenylphosphine-N,P]nickel(II), the Ni-N and Ni-P distances are greater and the N-Ni-P ligand bite angles smaller than those observed in a series of related complexes with square-planar nickel.