The copolymerization of ethene with carbon monoxide catalyzed by [Pd(OAc)(2)(dppp)] in an aprotic solvent such as 1,4-dioxane or nitromethane is efficiently promoted both by H2O and HCOOH and yields a perfectly alternating polyketone (PK). The influence of the concentration of the promoters, pressure and temperature on the catalyst productivity and the limiting viscosity number (LVN) has been studied. The productivity increases with the increase of temperature and pressure. The LVN increases upon increasing the pressure and lowering the temperature. At 363 K and 9.0 MPa, in HCOOH/H2O/1-4,dioxane (2.7/1.35/1 molar ratio), the productivity is 37.50 kgPK (gPd h)(-1) (LVN 2.77 dLg(-1)). LVN lowers upon increasing the concentration of the acid, suggesting that it is involved in the protonolysis chain-transfer process. (C) 2012 Elsevier B.V. All rights reserved.