K. Takegoshi

High-resolution solid-state 13C nuclear magnetic resonance study on poly(vinyl alcohol)/poly(vinylpyrrolidone) blends

Abstract The miscibility and domain structure of poly(vinyl alcohol)/poly(vinylpyrrolidone) (PVA/PVP) blends are investigated by high-resolution solid-state 13 C nuclear magnetic resonance methods. The observed 13 C spectra and the intermolecular cross-polarization of the blends suggest a hydrogen-bonding interaction between the two polymers. 1 H T 1 and T 1 ϱ results indicate that the blends are miscible at all compositions on a scale of 200–300 A. On a scale of 20–30 A, however, the miscibility of the blends depends significantly on the composition. When the PVA composition is more than 46 wt%, the blends are composed of two phases, an amorphous miscible phase of PVP plus PVA and a pure PVA phase. The crystallinity of the PVA phase decreases rapidly with decreasing PVA composition. When the PVA composition is less than 46 wt%, the blend is completely miscible. The composition of PVA phase in the blends was inferred from the results of 1 H T 1 ϱ .

Effects of blending on local chain dynamics and glass transition: Polystyrene/poly(vinyl methyl ether) blends as studied by high‐resolution solid‐state 13C nuclear magnetic resonance spectroscopy

To evaluate effects of blending on molecular motion of the individual polymer components in a compatible polymer blend, polystyrene/poly(vinyl methyl ether)(PS/PVME), the temperature dependence of 13C nuclear magnetic resonance linewidth for CH carbon resonance of PVME was studied under conditions of magic‐angle spinning and proton dipolar decoupling. The observed temperature dependence was satisfactorily explained by assuming the following effects of molecular motion: (1) averaging the dispersion of isotropic chemical shifts in the glassy state and (2) the interference between local anisotropic motion and high‐power proton decoupling. The activation parameters for motion of PVME of the blends were determined, and the compositional dependence is discussed. It is concluded that microscopically homogeneous mixing is achieved for PS/PVME blends.

High-resolution solid state 13C n.m.r. study of the interpolymer interaction, morphology and chain dynamics of the poly(acrylic acid)/poly(ethylene oxide) complex

The interpolymer interaction, morphology and chain dynamics of the poly(acrylic acid)/poly(ethylene oxide) (PAA/PEO) complex are examined by using 13C CP/MAS n.m.r. methods. By analysing 13C CP/MAS spectra of the complex we conclude that there exist three hydrogen bonding forms for the carboxyl group of PAA, namely: (1) the complex form, interpolymer hydrogen bonding between PEO molecules; (2) the dimeric form, intrapolymer hydrogen bonding within PAA molecules; and (3) the free form, no particular form of hydrogen bonding. The morphology of the complex is investigated by the 1H spin-lattice relaxation time in the laboratory frame (T1), and that in the rotating frame (T1ρ). We found that the domain sizes of the three hydrogen bonding forms of PAA are less than a few tens of angstroms, and the PAA/PEO complex is miscible on a molecular level. Further, temperature dependence of 13C linewidth (T2) is examined to study effects of complexation on the molecular motion of the component polymers. The temperatures at which the maximum linewidths are observed for the main chain carbon of PEO and PAA in the PAA/PEO complex are 310 and 362 K, respectively. This indicates that the motional heterogeneity is present in spite of a single Tg for the PAA/PEO complex. Further, we discuss the structural difference between the poly(methacrylic acid)/PEO complex and the PAA/PEO complex.

High-resolution solid-state 13C nuclear magnetic resonance study of a polymer complex: poly(methacrylic acid)/poly(ethylene oxide)

Abstract The inter-polymer interaction, morphology and molecular motion of the poly(ethylene oxide)/ poly(methacrylic acid) (PEO/PMAA) complex were investigated by measuring various nuclear magnetic resonance parameters, such as 13 C chemical shift, 1 H T 1 , 1 H T 1 ρ , 1 H T 2 and 13 C T 2 . For the complex, we observed two peaks for the carboxyl carbon of PMAA. We assigned the higher-field resonance to the carboxyl group that forms hydrogen bonds to PEO (the complex form), and the lower-field one to the group that forms hydrogen bonds among PMAA (the dimeric form). It is shown that, for temperatures within 100 K below T g , the complex form easily breaks up and rearranges to the dimeric form. For the complex, the 13 C T 2 and 1 H T 2 reveal that PEO is mobile, whereas PMAA is rigid. This different mobility between PEO and PMAA may facilitate breakage of the hydrogen bonding between PEO and PMAA. Examination of 1 H spin diffusion in the complex reveals that the distance between PEO and PMAA in the complex is similar to that between PEO and PMAA in the dimeric form. These results show that the PMAA in the dimeric form does not aggregate to form a domain structure, and that the PEO/PMAA complex is miscible on a segmental scale. Furthermore, the thermal degradation of PMAA in the complex was examined. Dehydration occurs in the dimeric form to produce anhydride, and the reaction temperature is much lower than that of pure PMAA.

Phase separation and thermal degradation of poly(vinyl alcohol)/poly(methacrylic acid) and poly(vinyl alcohol)/poly(acrylic acid) systems by 13C c.p./m.a.s. n.m.r.

Abstract Phase separation and chemical structure changes occurring during thermal degradation are studied by high-resolution solid-state 13C n.m.r. methods for poly(vinyl alcohol)/poly(methacrylic acid) ( PVA PMAA ) = 1 1 complex and poly(vinyl alcohol)/poly(acrylic acid) ( PVA PAA ) = 1 1 blend. 13C cross-polarization/magic-angle spinning spectra and 1H T1ϱ are measured for samples subjected to various heat treatments. The results indicate that when the systems are heated to higher temperatures, phase separation occurs first because of the dissociation of intermolecular hydrogen bonding between the two different polymers. Further increases in temperature bring about thermal degradation. Degradation products of the complex and the blend are similar to those of the corresponding single-polymer systems. The thermal degradation temperatures for the complex and the blend are lower than for the single-polymer systems. This is ascribed to the loss of the crystalline phase of the PVA component and a lowering of glass transition temperatures of the PMAA and PAA components in the miscible system.

13C c.p./m.a.s. n.m.r. study on the miscibility and phase separation of a polystyrene/poly(vinyl methyl ether) blend

We investigate the miscibility of a polystyrene/poly(vinyl methyl ether) (PS/PVME) blend using nuclear magnetic resonance spectroscopy. We examine 1 H spin-lattice relaxation times in both the laboratory ( T 1H ) and rotating ( T 1ρH ) frames at various temperatures. At temperatures lower than the glass transition temperature ( T g ) of the blend, the observed 1 H relaxation time of PS is equal to that of PVME, showing that the 5/5 PS/PVME blend is miscible on a scale of 20–30 A. At temperatures much higher than T g , the observed 1 H relaxation curve ( T 1 ρ H ) of PS apparently differs from that of PVME. They are not single exponentials. The non-exponential decays are analysed taking into account spin diffusion; the 1 H spin diffusion rate between PS and PVME is found to be ∼ 1000s −1 at 38°C. This spin diffusion rate is too slow for the T 1ρH values of PS and PVME to coincide with each other. This is attributed to the fast molecular motion of PVME. The 1 H relaxation curve of the phase-separated blend formed by heating above the lower critical solution temperature is markedly different from that of the homogeneous blend. On the assumption that 1 H spin diffusion does not occur between phase-separated domains, we analyse the 1 H relaxation curve of each component polymer and obtain the stoichiometry of the phase-separated domains. We conclude that the phase separation of the 5/5 PS/PVME blend is initiated by spinodal decomposition; the phase separation rate is 0.5 min −1 at 140°C.

Effects of sample spinning on “overtone” NMR

Abstract Effects of sample spinning on “overtone” NMR of quadrupole nuclei with spin = 1 in the solid is investigated. A possibility for reducing second-order quadrupole broadening by DAS and DOR methods is also discussed.

Determinationof the 14N quadrupole coupling tensor of an ℓ-alanine single crystal by overtone NMR

Abstract The overtone NMR approach was examined for determination of the quadrupole coupling tensor of the 14 N nucleus in a single crystal and demonstrated for l-alanine.

Solid state deuteron NMR study of a polystyrene/poly(vinyl methyl ether) blend

Abstract The 2H NMR spectra of main-chain deuterated polystyrene in a polystyrene/poly(vinyl methyl ether) (PS/PVME) blend are observed at various temperatures. The spectra are simulated by assuming microbrownian motion and vibrational motion. The temperature and the composition dependences are discussed. A distribution of mobility in space is suggested. The distribution is caused by spatial microheterogeneity in the blend.

Phase separation and microscopic homogenization of polystyrene/poly(vinyl methyl ether) by solid state 2H NMR

Abstract The time dependence of the 2H NMR spectra of a polystyrene/poly(vinyl methyl ether) blend in the course of phase separation is studied. It is found that the two processes, fast and slow, are involved in phase separation. The fast process is ascribed to the spinodal decomposition and the slow process is interpreted in terms of the homogenization of microheterogeneity in the phase-separated domains.