The α and β structural forms of poly(tetramethylene terephthalate): a study by broad line nuclear magnetic resonance

Abstract

Broad line nuclear magnetic resonance measurements have been carried out on oriented poly(tetramethylene terephthalate). The second moment was determined as a function of specimen orientation for the polymer in its unstrained state, and also under extension, where previous X-ray diffraction measurements have shown that the crystal structure changes from the α form (relaxed) to the β form (strained). The n.m.r. results for the stretched specimen are consistent with the molecular conformation being close to full extension, and agree quantitatively with the crystal structure proposed by Hall and Pass. The n.m.r. results for the unstrained material are, however, not in agreement with any of the crystal structures which have been proposed and suggest that, contrary to present conclusions, the conformation and orientation of the central methylene pairs in the glycol residue must remain substantially unchanged in the transformation from the α to the β form.