Properties of liquid and cured phenolformaldehyde (PF) resin modified with esters were analyzed in this study. Esters with different carbon chain lengths, both in the acid and alcohol groups, were applied in the experiments. It was found that the modification of phenolic resin with applied esters does not deteriorate its pot life at the temperature of 20 degrees C. It results in an increase of its reactivity at higher temperatures, manifested in the shortening of gel time at 130 degrees C and a decrease of activation energy. Results of FTIR tests of polycondensed modified PF resin showed that products of alkali hydrolysis of esters not only catalyze the curing reaction of resin, but also become embedded in its structure. (c) 2007 Wiley Periodicals, Inc.