Masahito Kanekiyo

A structural and dynamic study of poly(vinyl alcohol) in the gel state by solid-state 13C NMR and 1H pulse NMR

1H pulse NMR and high-resolution solid-state 13C NMR spectra of poly(vinyl alcohol) (PVA) gel were measured to clarify the structure and dynamics of the immobile component of the gel. From 1H pulse NMR experiments, it was found that the T2 signal is mainly composed of three components. The long T2 component was assigned to the mobile component which comes from the noncrosslinked region, the intermediate T2 component corresponds to the intermediate immobile component which comes from the vicinity of the crosslinked region, and the short T2 component corresponds to the immobile component which comes from the crosslinked region in the PVA gel. From high-resolution solid-state 13C NMR experiments, the mechanism of gel formation was satisfactorily elucidated. Further, dynamic viscoelastic modulus measurements were carried out. These experimental results were satisfactorily explained on the basis of the NMR results.

Molecular Dynamics in Chiral Smectic Liquid-Crystalline Phases Studied by Solid State 13 C-NMR Measurements

The temperature dependence of the spin-lattice relaxation time T 1 is investigated in an antiferroelectric liquid crystal, (S)-4-(1-methylheptyloxy-carbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate (S-MHPOBC) by means of solid-state 13 C-NMR spectroscopy. The spin-lattice relaxation time T 1 of almost all of aromatic carbons has a minimum at the temperature region of the SmC A * phase in the temperature dependent curves, because the correlation time τ c of the molecular motion corresponds to the Larmor frequency ω 0 of 100 MHz in the present measurements. As for the aliphatic carbons in a flexible chain, the value of T 1 increases with increasing temperature, because the molecular motion characterized by τc is faster than the Larmor frequency ω 0 .

A study of the gelation mechanism of poly(vinyl alcohol) in aqueous solution by high-resolution solid-state 13C NMR spectroscopy

Abstract 13 C CP/MAS NMR spectra of aqueous PVA solution were measured at −40°C and room temperature. From these experimental results, it was found that the freeze–thaw cycle process induces the formation of intermolecular hydrogen bonds and so the formation of the PVA/water gel. The mechanism of the gelation was proposed.

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

Abstract High-resolution solid-state 13C NMR spectra of (ethylene–vinyl alcohol) copolymers (EVOH) with various ethylene contents in the solid-state and their 13C spin-lattice relaxation times, T1, were measured, in order to elucidate the structure and dynamics of the copolymers. From these experimental results, the structural change of the EVOHs with changes of the ethylene content was successfully elucidated. Further, it is found that the 13C T1 for the CH carbon of the vinyl alcohol unit is mainly composed of two components. The fractions of short and long T1 components increase and decrease with an increase in the ethylene fraction, respectively. From these experimental results, it can be said that changes of the ethylene content in the copolymers lead to large changes in their structure and dynamics.

A structural study of water in a poly(vinyl alcohol) gel by 17O NMR spectroscopy

Abstract 17 O NMR spectra of poly(vinyl alcohol) (PVA) gel as prepared by repeating the freezing/thawing cycle were measured, in order to elucidate the structure and dynamics of water in PVA gel. From these experimental results, it was found that the 17 O chemical shift position of water in PVA gel moves downfield with an increase in the number of freezing/thawing cycles. Ab initio MO GIAO-CHF and FPT INDO calculations on the hydrogen-bonded water model suggest that such a downfield shift comes from a reduction of hydrogen-bond length between water molecules or between water molecule and hydroxyl group of PVA. 17 O spin–lattice relaxation times ( T 1 ) of water in the gel were measured, in order to elucidate dynamics of water in the gel. The T 1 value is decreased with an increase in the number of freezing/thawing cycles. This means that the mobility of water in the gel is reduced with an increase in the degree of gelation. Further, 17 O NMR spectra of PVA gel, which was kept at room temperature after the temperature elevation until 80°C, were measured. Some peaks of water that come from different structures in the PVA gel appeared. Further, detailed discussion on the structure of water in PVA gel was discussed.

13C-NMR Studies on Fluctuation of Rod-Like Molecules in Solution: Molecular Dynamics in a Polar Solvent of CDCl3

To investigate the molecular dynamics of rod-like molecules in solution, 13C-NMR measurements of a liquid crystalline material (4-(1-methylheptyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate: MHPOBC) with a CDCl3 solvent are carried out. When MHPOBC leaves the solution and deposits as crystals, peak broadening, which may result from a slowing down of molecular motion, occurs simultaneously. In addition, the correlation time τc of the corresponding molecular motion is estimated to be approximately 10−8 s by the spin-lattice relaxation time T1 measurements.