The results are presented on the synthesis of new modifiers and functioning of amine modifiers for unsaturated polyester resins, obtained by reacting ethylene oxide or propylene oxide with phenyl-1,4-diamine. Also the effect of the modifiers and cobalt accelerator on the reactivity of resins was studied. When used in the amount of up to 2 wt %, the amines substantially (several times) reduced the gelation time of modified unsaturated polyesters. The reactivity of resins, however, improved in expense of their stability. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 311-321, 2011