SEGMENTAL SIZE OF POLY(ETHYLENE-TEREPHTHALATE) DETERMINED BY OPTICAL BIREFRINGENCE AND ESR SPIN-PROBE METHOD

The segmental size in amorphous poly(ethylene terephthalate) (PET) was determined by two methods: a) from deformational behavior of amorphous samples in the elastic state by optical birefringence measurement, and b) from dynamic behavior of a small spin probe by ESR measurement of correlation times. The use of the network model for orientation of segments in amorphous polymer and of the generalized free-volume model for re-orientation of the probe in the amorphous phase gave comparable values of n = 2.3 and 2.1 structural units/segment. We conclude that trans reversible gauche conformational transitions of rather small macromolecular segments are the basic motion mechanism in alpha(a)-segmental mobility in PET.