A process for producing olefin polymers, which comprises the steps of polymerizing an olefin monomer in a polymerization zone in the presence of a catalyst comprising a transition metal compound to form an olefin polymer, and adding at the end of or downstream from the polymerization zone a composition having a weight averaged molecular weight of at least 100 and containing a group R, a cation Y, an anionic group --C(R.sup.1).sub.2--X.sup.-, and optionally a group --C(R.sup.1).sub.2--X--H, the composition having a relative the composition having a relative mole fraction n of cations Y and a relative mole fraction m of group --C(R.sup.1).sub.2--X--H, wherein 0