ON THE STRUCTURE OF GLASSY POLYMERS - 3. SMALL-ANGLE X-RAY SCATTERING FROM AMORPHOUS POLYETHYLENE TEREPHTHALATE.

Experimental data are presented which show that the small-angle x-ray scattering (SAXS) from glassy polyethylene terephthalate (PET), varies with scattering angle in a manner generally similar to that observed previously for glassy polycarbonate and PMMA. The SAXS intensity from PET decreases sharply with increasing angle in the very small angle region (2 theta less than 10 min), followed by a more gradual decrease over the angular range between 10 min and 45 min; this is followed by a nearly constant intensity over a sizable range of angle which gradually merges with the tail of the main wide-angle diffraction maximum. As with polycarbonate and PMMA, the measured SAXS in the constant intensity region corresponds closely with that expected for thermal density fluctuations frozen-in at the glass transition. The present results are inconsistent, both in magnitude and form of the SAXS intensity, with the presence of nodular features as representative of the bulk polymer. It is suggested that the nodular structures seen in this polymer be associated with surface effects. It is also suggested that the structure of glassy PET be regarded as that of a random amorphous polymer, with a small concentration of heterogeneities - some perhaps crystallites - superimposed on thermal density fluctuations frozen-in at the glass transition.