ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
A polyester composed of trans-2,5-linked tetrahydropyran rings (4t) was synthesized by direct polycondensation of trans-5-hydroxytetrahydropyran-2-carboxylic acid (5t) using N-methyl-2-chloropyridinium iodide or triphenylphosphine and hexachloroethane as condensing agents in pyridine at 25 or 50°C. The hydroxycarboxylic acid 5t was polymerized also with dibutyltin oxide, although longer reaction times were required. The polyester 4t 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 (4c) 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 4t 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 for dimer models for 4c and 4t 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 4t decompose at 300°C in nitrogen atmosphere, approximately 150°C higher than the isomeric polyester 2.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1991.021920805
