2-Dicyclohexyl- and 2-diphenylphosphinophenol, CCHH and PPHH, react with Ni(1,5-COD)(2) to form catalysts for polymerization of ethylene in or copolymerization with alpha-olefins. The more P-basic CCHH/Ni catalyst allows concentration-dependent incorporation of olefins to give copolymers with isolated side groups and higher molecular weights, whereas the PPHH/Ni catalyst undergoes mainly stabilizing interactions with the olefins and leads to ethylene oligomers with no or marginal olefin incorporation. Pressure-time plots of the batch reactions show that the ethylene conversion is usually slower by catalysis with CCHH/Ni than by PPHH/Ni. The microstructure of the copolymers was determined by C-13 NMR spectra, the number of side groups per main chain was estimated by H-1 NMR analyses. (c) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 258-266, 2009