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

Phase Structure of Ethylene−Vinyl Alcohol Copolymers As Revealed by Variable-Temperature Solid-State High-Resolution 13C NMR Spectroscopy

“…The detailed assignment of these methine carbon peaks is still a controversial topic. [3][4][5] Peaks from 20 to 50 ppm correspond to methylene carbons either in V or in E units. The assignments of these methylene peaks are shown in Figure 1.…”

“…These methine carbon peaks can be resorted to central methine carbons in different triad sequences (mmVVV, mrVVV, rrVVV, mVVE, rVVE, and EVE, where E and V represent ethylene unit and vinyl alcohol unit and m and r represent meso and racemic, respectively) and intra/inter-molecular hydrogen-bonding interactions between hydroxyl groups. The detailed assignment of these methine carbon peaks is still a controversial topic. − Peaks from 20 to 50 ppm correspond to methylene carbons either in V or in E units. The assignments of these methylene peaks are shown in Figure .…”

“…1,2 There have been some reports on room-temperature solid-state highresolution 13 C NMR study on EVOH. [3][4][5] However, due to the difficulties in discriminating signals from different phase structures and the difficulties in peak assignment, the technique failed to provide straightforward phase structure information as it did in the studies on many other semicrystalline polymers, such as polyethylene. 6 To discriminate signals from different phase structures of multiphase polymers by the solid-state NMR techniques, it is usually required that the molecular chains in different phases have marked difference in mobility.…”

“…The phase structure of semicrystalline ethylene−vinyl alcohol copolymer (EVOH) has been an interesting research subject for many years. Many factors, including the composition and the sequence distribution of the copolymer, the tacticity of the vinyl alcohol segments, the hydrogen-bonding interactions between the hydroxy groups, and also the processing conditions, may have influences on the phase structure. , There have been some reports on room-temperature solid-state high-resolution 13 C NMR study on EVOH. − However, due to the difficulties in discriminating signals from different phase structures and the difficulties in peak assignment, the technique failed to provide straightforward phase structure information as it did in the studies on many other semicrystalline polymers, such as polyethylene …”

Structural and Dynamic Study of Ethylene−Vinyl Alcohol Copolymer Gels by 1H Pulse NMR and Solid-State 13C NMR

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1 H pulse NMR and solid-state 13 C NMR spectra of ethylene-vinyl alcohol copolymer (EVOH) gels were measured as a function of ethylene content, and furthermore, the 13 C spin-lattice relaxation times (T1) and the 1 H spin-spin relaxation times (T2) have been measured, to elucidate the structure and dynamics of the mobile and immobile regions in the gels. From the 1 H pulse NMR experimental results, it is found that the 1 H T2 signal is mainly composed of two or three kinds of components with different molecular motions.

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