Unsaturated polyesters (UPE) were chain extended with three different epoxy group containing compounds. The molecular weight increase was monitored using gel permeation chromatography (GPC). The polymers obtained were characterized by FTIR and H-1 NMR, and styrene solubility and gel time. The polyesters were then diluted with styrene and cured with a radical initiator and compared with a commercial reference polyester. Thermal and mechanical properties of the cured polyesters were characterized by dynamic mechanical analysis (DMA) and thermal gravimetric analysis (TGA). The results show that UPE can be chain extended with epoxy containing compounds which substantially shortens the condensation polymerization during manufacture, without compromising their thermal and mechanical properties. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1184-1191, 2009