The composition of polyester polyols derived from terephthalic acid (TPA) and diethylene glycol (DEG) was examined. The synthesis of individual oligomers 1,n is described. The compounds were characterized with H-1 and C-13 NMR, mass spectrometry, and elemental analyses. The resonance signals arising from aromatic protons in 1,n = 1-3 were identified in H-1 NMR spectra of TPA-DEG condensates. From H-1 NMR studies and chromatographic separation, it was concluded that the condensation of TPA and DEG in a 1:2 molar ratio results in a mixture of linear oligomers 1 with the average h varying from 1.1 to 2.2, and containing about 2% of cyclic oligomer 2. (C) 2003 Wiley Periodicals, Inc.