Polyurethanes containing carboxylate groups were synthesized by using phenolphthalins as chain extenders. The resulting polymers were converted into ionomers by treating with metal acetates. The diols and polyurethanes were characterized by both Fourier transform nuclear magnetic resonance (FTn.m.r.) and Fourier transform infra-red (FTi.r.) spectroscopy. The thermal stabilities of the diols and polymers were analysed by thermogravimetric analysis.