C-13 AND H-1 NUCLEAR-MAGNETIC-RESONANCE RELAXATION OF POLY(ETHYLENE-TEREPHTHALATE), POLY(ETHYLENE ISOPHTHALATE) AND THEIR COPOLYESTER IN SOLUTION - A MOLECULAR-MOTION STUDY

C-13 nuclear magnetic resonance spin-lattice relaxation times (T-1) an d nuclear Overhauser enhancement factors C-13{H-1} (NOEf) have been me asured on solutions of poly(ethylene terephthalate) (PET), poly(ethyle ne isophthalate) (PEI) and poly(ethylene isophthalate-co-terephthalate ) (PEIT) in d(2)-tetrachloroethane. The T-1 and NOES values are well d escribed by a log X(2) distribution of correlation times, while the is otropic model appears to be inadequate. The average correlation times (tau(0)) and the distribution parameters (p) of carbons and protons sh ow features that are explained by invoking rotations and/or oscillatio ns of terephthalic and isophthalic rings around the C1-C4 axis.