Studies on the phase structure of ethylene‐vinyl acetate copolymers by solid‐state 1 H and 13 C NMR

The phase structure of a series of ethylene‐vinyl acetate copolymers has been investigated by solid‐state wide‐line 1 H NMR and solid‐state high‐resolution 13 C NMR spectroscopy. Not only the degree of crystallinity but the relative contents of the monoclinic and orthorhombic crystals within the crystalline region varied with the vinyl acetate (VA) content. Biexponential 13 C NMR spin–lattice relaxation behavior was observed for the crystalline region of all samples. The component with longer 13 C NMR spin–lattice relaxation time ( T 1 ) was attributed to the internal part of the crystalline region, whereas the component with shorter 13 C NMR T 1 to the mobile crystalline component was located between the noncrystalline region and the internal part of the crystalline region. The content of the mobile crystalline component relative to the internal part of the crystalline region increased with the VA content, showing that the 13 C NMR spin–lattice relaxation behavior is closely related to the crystalline structure of the copolymers.