AbstractA polyester composed oftrans‐2,5‐linked tetrahydropyran rings (4t) was synthesized by direct polycondensation oftrans‐5‐hydroxytetrahydropyran‐2‐carboxylic acid (5t) usingN‐methyl‐2‐chloropyridinium iodide or triphenylphosphine and hexachloroethane as condensing agents in pyridine at 25 or 50°C. The hydroxycarboxylic acid5twas polymerized also with dibutyltin oxide, although longer reaction times were required. The polyester4tis soluble inm‐cresol and halogenated protic solvents such as 2,2,2‐trifluoroethanol, trifluoroacetic acids and dichloroacetic acid, but insoluble in chloroform and dichloromethane in which the correspondingcis‐isomer (4c) composed ofcis‐2,5‐linked tetrahydropyran rings is soluble. According to conformational energy calculations, the repeating unit exists predominantly as a conformer in which both the exocyclic oxygen and the carbonyl carbon in the backbone of the chain are located in the equatorial positions of the tetrahydropyran ring; in other words, the chain of4ttakes a linear conformation. On the other hand, the exocyclic oxygen in the repeating unit of4coccupies an axial position of the tetrahydropyran ring and the chain is winding. Conformational energies for dimer models for4cand4twere also estimated by means of force field calculations. These polyesters are partially crystalline according to their X‐ray diffraction patterns. Both polyesters show birefringence at or above 200°C. The polyesters4cand4tdecompose at 300°C in nitrogen atmosphere, approximately 150°C hi