Water-soluble complexes based on enolatoimine ligands bearing electron-withdrawing trifluoromethyl groups [kappa(2)-N,O-{2,6-R2C6H3N=C(H)C(COCFC3)=C(O)CF3}NiMe(L)] (1a, R = 3,5-(CF3)(2)C6H3, L = Me(OCH2CH2)(n)NH2; 1b, R = 3,5-(CF3)(2)C6H3, L = TPPDS; 2b, R = Pr-i, L = TPPDS; 2c, R = Pr-i, L = TPPTS with TPPDS = PhP(p-C6H4SO3Na)(2) and TPPTS = P(m-C6H4SO3Na)(3)) were prepared. These complexes polymerize ethylene to very small (10-30 nm) semicrystal line particles of high molecular weight (up to M-w 1.6 x 10(6) g mol(-1)) polymer with a degree of branching (7-63 branches per 1000 C atoms) and thus crystallinity (<= 25-50%) and melt transition temperatures (T-m = 75-129 degrees C) variable over a large range, depending on the substituents of the N-aryl moiety (2,6-R2C6H3), and the polymerization temperature. The catalysts are stable for hours under polymerization conditions (50 degrees C) in the highly disperse aqueous System.