Three isomeric poly(2-octadecyl-1,3-trimethylene phthalate)s were prepared by melt transesterification of the corresponding diphenyl ester and 2-octadecyl-1,3-propanediol. Intrinsic viscosity, size exclusion chromatography and light scattering determinations yielded weight-average molecular masses of 110 000 and higher. High-resolution, solution C-13 n.m.r. spectroscopy analysis of both the diphenyl ester precursors and polyesters identified the main-chain units, the isomeric aromatic acid residue and glycol carbons, the linking and the terminal ends of the octadecyl side chain, and finally allowed detection of phenyl ester end groups at 1-2% level. No absorption band due to hydroxyl end groups was monitored in the i.r. polyester spectra. I.r. spectroscopy, d.s.c. and powder X-ray diffractometry provided a clear indication of the crystallinity of the prepared polyesters. The relevant melting enthalpy values and X-ray diffraction patterns were typical of comb-shaped polymers in which the paraffinic side chains crystallize independently with their characteristic hexagonal packing.