An investigation of the ethylene polymerization with meso ansa metallocenes of group 4 allows clarifying some aspects of the branching formation observed in the polyethylene produced with these catalysts. The meso structure of the zirconocene precursor is more effective in promoting the chain growing isomerization when indenyl ligands bear no substituents. But the same coordinating neighborhood when surrounding the Ti(IV) or Hf(IV) ion gives rise to complexes not effective in the ethyl-branched polyethylene synthesis. On the other hand, several activators in combination with meso-ethylenebis(1-indenyl)Zr(CH3)(2) produce catalysts able to polymerize ethylene to ethyl-branched polyethylene. No difference has been detected in the amount of branches with respect to that observed with MAO-activated meso-ethylenebis(1-indenyl)ZrCl2.