A structural study of (ethylene-vinyl alcohol) copolymers by high-resolution solid-state C-13 NMR

High-resolution solid-state C-13 NMR spectra of (ethylene-vinyl alcohol) co polymers (EVOH) with various ethylene contents in the solid-state and their C-13 spin-lattice relaxation times, T-1, were measured, in order to elucid ate the structure and dynamics of the copolymers. From these experimental r esults, the structural change of the EVOHs with changes of the ethylene con tent was successfully elucidated. Further, it is found that the C-13 T-1 fo r the CH carbon of the vinyl alcohol unit is mainly composed of two compone nts. The fractions of short and long T-1 components increase and decrease w ith an increase in the ethylene fraction, respectively. From these experime ntal results, it can be said that changes of the ethylene content in the co polymers lead to large changes in their structure and dynamics. (C) 1999 El sevier Science Ltd. All rights reserved.