Structural and dynamic study of ethylene-vinyl alcohol copolymer gels by 1H pulse NMR and solid-state 13C NMR

H-1 pulse NMR and solid-state C-13 NMR spectra of ethylene-vinyl alcohol copolymer (EVOH) gels were measured as a function of ethylene content, and furthermore, the C-13 spin-lattice relaxation times (T-1) and the H-1 spin-spin relaxation times (T-2) have been measured, to elucidate the structure and dynamics of the mobile and immobile regions in the gels. From the H-1 pulse NMR experimental results, it is found that the H-1 T-2 signal is mainly composed of two or three binds of components with different molecular motions. The long T-2 component is assigned to correspond to the mobile region, which comes from the un-cross-linked region, the short T-2 component corresponds to the immobile region, which comes from the cross-linked region, and the intermediate T-2 component corresponds to the intermediate region between the mobile and immobile regions, which comes from the vicinity of the cross-linked region in the EVOH gel. Furthermore, from the solid state C-13 NMR experimental results, it is found that the formation of hydrogen bonds between the hydroxyl groups in vinyl alcohol parts of EVOH copolymers with high vinyl alcohol fraction and the formation of hydrophobic interactions between the methylene groups in ethylene parts of EVOH copolymers with high ethylene fraction contributes to its gel formation.