New ethylene polymers having broad molecular weight distribution and long-chain branching, above all at high molecular weight fractions; the polymers have strain hardening equal or higher than 1.4 (at constant elongational rate of 0.5 s−1, at 150° C.), branching index g′ equal or lower than 0.9 (at Mw of 2·106 g/mol). The polymers are prepared by using a mixed catalyst system comprising a polymerization catalyst based on a late transition metal component having a tridentate ligand, and a Ziegler polymerization catalyst annealed at a temperature higher than 100° C., for a time of at least 10 minutes.