Synthesis and properties of quasi‐rigid polyesters containing 2,5‐disubstituted tetrahydropyran rings in their main chains

Abstract

A polyester composed of trans-2,5-linked tetrahydropyran rings (4 t) was synthesized by direct polycondensation of trans-5-hydroxytetrahydropyran-2-carboxylic acid (5 t) using N-methyl-2-chloropyridinium iodide or triphenylphosphine and hexachloroethane as condensing agents in pyridine at 25 or 50 "C. The hydroxycarboxylic acid 5 t was polymerized also with dibutyltin oxide, although longer reaction times were required. The polyester 4 t is soluble in m-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 corresponding cis-isomer (4 c) composed of cis-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 of 41 takes a linear conformation. On the other hand, the exocyclic oxygen in the repeating unit of 4c occupies an axial position of the tetrahydropyran ring and the chain is winding. Conformational energies of dimer models for 4c and 4 t were 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 polyesters 4c and 4 t decompose at 300°C in nitrogen atmosphere, approximately 150 "C higher than the isomeric polyester 2.

Synthesis and properties of new polyesters having tetrahydrofuran rings in their main chains

“…Methyl trans-and cis-4-hydroxytetrahydrofuran-2carboxylates 5a and 5b were synthesized starting from methyl glycolate (7, R = H ) and diethyl maleate ( 8 ) as illustrated in Scheme 1. Thus, the Michael addition of the anion of 7 to 8 followed by intramolecular cyclization yielded diethyl 4-0x0-10 5a -5 c Scheme 1.…”