High-resolution Solid-state Nuclear Magnetic Resonance Research Articles

Miscibility in blends of poly (4-vinylpyridine)/poly (4-vinylphenol) as studied by 13C solid-state NMR

The miscibility of poly (4-vinylpyridine) (P4VP) with poly (4-vinylphenol) (PVPh) blends was investigated over a wide range of compositions by differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR), and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. DSC results show that the Tgs of the P4VP/PVPh blends are much higher than those of the calculated weight-average values. The proton spin–lattice relaxation times in the laboratory frame, T1(H), and the rotating frame, T1ρ(H), were studied as a function of blend composition. T1(H) and T1ρ(H) results demonstrate that the spin diffusion can completely average out the entire relaxation process. It was also found that the intimate mixing of the polymer blends restricts the local chain mobility.

A Multi-nuclear Multiple-Field Nuclear Magnetic Resonance Study of the Y2O3−Al2O3 Phase Diagram

We have been investigating several compounds belonging to the Y2O3−Al2O3 phase diagram by means of aluminum-27, oxygen-17, and yttrium-89 high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. All aluminum, oxygen and yttrium sites of the five crystalline compounds C-Y2O3, Y4Al2O9, YAlO3, Y3Al5O12, and α-Al2O3) have been resolved and the NMR parameters deduced. AlVI sites exhibit isotropic chemical shift δiso between 0 and 10 ppm and small quadrupolar coupling constant CQ, whereas AlIV are located between 70 and 80 ppm and show large CQ. 17O resonances are characterized by small CQ and δiso ranging from 72 ppm (Al2O3) to 358 ppm (Y2O3) and showing a strong sensitivity to the nature of the second coordination sphere of oxygen as well as its coordination number. 89Y δiso are found between 184 and 314 ppm and are not strongly correlated to the coordination state of yttrium, the chemical shift anisotropy being found moderate (∼100 ppm). On the basis of the results obtained with the crystalline phases, we have characterized the oxygen environment in a glassy sample of composition Y3Al5O12 and described the variation of the local structure during the crystallization process of YAlO3 from the sol−gel raw product. In the vitreous state, oxygen's environments can be described in terms of OYk Al4-k sites, with respective populations not distributed in a purely random fashion, and two types of 5-fold-like aluminum environments can be evidenced. A quantitative description of the heat treatments of the YAlO3 precursor is given by 17O NMR experiments in terms of Y4Al2O9, Y3Al5O12, and amorphous phases formed. New oxygen environments are also evidenced and may be attributed to the hexagonal metastable form of YAlO3.

In-situ multinuclear solid-state NMR spectroscopy under continuous-flow conditions for investigations of Ziegler–Natta catalyzed propene polymerization

Multinuclear ( 1H, 13C, 27Al) high-resolution solid-state nuclear magnetic resonance (NMR) during the continuous-flow of propene monomer was applied to analyze in-situ propene polymerization on Ziegler–Natta catalysts. A supported Ziegler catalyst activated with triethylaluminum and AA-TiCl 3 were employed as catalysts. The time-dependent change in the spectral peak intensities during the propene polymerization with both catalysts was measured using 13C CP MAS (cross-polarization with magic angle spinning) NMR and 1H MAS NMR. The states of the aluminum complex in the catalysts were studied using 27Al MAS NMR, which is sensitive to the coordination and symmetry of the local environment around the aluminum nuclei. Peculiarities of the polymerization kinetics, the crystalline states of the nascent polypropene formed on the catalyst surface, and the state of aluminum coordination and environment during the early stage of the propene polymerization under continuous-flow condition are discussed.

Miscibility of poly(ethyl oxazoline)/poly(4-vinylphenol) blends as investigated by the high-resolution solid-state 13C NMR

The miscibility of poly(ethyl oxazoline) (PEOx) and poly(4-vinylphenol) (PVPh) blends were investigated by differential scanning calorimeter (DSC), Fourier-transform infrared spectroscopy (FTIR), and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. It was found that PEOx was miscible with PVPh as shown by the existence of single composition-dependent glass transition temperature ( T g) in the whole composition range. FTIR results revealed strong hydrogen bonding between the carbonyl groups of PEOx and the hydroxyl groups of PVPh. 13C cross-polarization (CP)/magic angle spinning (MAS)/dipolar decoupling (DD) spectra of the blends showed significant chemical shift changes, which support the FTIR results. The proton spin–lattice relaxation times in both the laboratory frame, T 1(H), and the rotating frame, T 1 ρ (H), were studied as a function of blend composition, and blends gave values longer than pure polymers. The T 1(H) results are in good agreement with the thermal analysis; i.e. the blends are completely homogenous on the scale of 30–40 nm. The T 1 ρ (H) results further indicate that the blends were homogenous on the scale of 2–3 nm.

The role of sodium during the hydration of alkali-activated slag

This paper presents the results of an investigation into the role of sodium cations during the hydration of alkali-activated slag (AAS). This subject was studied by a combination of powder X-ray diffraction, high-resolution solid-state nuclear magnetic resonance spectroscopy and atomic absorption spectrum analysis. It was found that: there is no evidence that sodium cations take part in cation interchange or play a catalytic role in the early stages of hydration; no sodium cations of a detectable quantity are chemically incorporated into the structure of C-S-H solid solution; and no hydrates of zeolitic type or other crystalline phases containing sodium are formed in the AAS pastes studied. It has been concluded that most sodium in AAS pastes is present in pore solution and may be partly sorbed by C-S-H, and that sodium cations may only have the effect of balancing and maintaining OH− anions during the AAS hydration. The structural incorporation of sodium cations in C-S-H is deemed very limited.

Residual dipolar couplings between quadrupolar nuclei in high resolution solid state NMR: Description and observations in the high-field limit

Nonsecular dipolar couplings between spin-12 nuclei that are in close proximity to quadrupolar spins have been extensively documented in solid state nuclear magnetic resonance (NMR), particularly when involving directly bonded S=13C, I=14N spin pairs. These couplings arise due to the quadrupole-induced tilting of I’s nuclear spin quantization axes, and their most notable characteristic is that they cannot be entirely averaged away by conventional magic-angle-spinning (MAS). Nonsecular dipolar couplings can also be expected to arise when both I and S are quadrupolar nuclei, even if these have hitherto not been analyzed in detail due to the interfering effects brought about by first- and second-order quadrupolar anisotropies. Yet, the advent of new high resolution techniques for studying half-integer quadrupole nuclei in solids such as multiple-quantum MAS or dynamic-angle-spinning can change this state of affairs. The present study presents a theoretical and numerical analysis on the results that can be expected from these techniques when applied to the observation of homonuclear or heteronuclear quadrupolar spin pairs in the high field limit. Variable field multiple-quantum MAS NMR results are then presented for a variety of compounds possessing 11B–14N, 11B–11B and 55Mn–55Mn spin pairs, that validate these theoretical predictions and illustrate the valuable information that can be extracted from analyzing these residual MAS couplings. The research potential as well as resolution limitations that according to theoretical calculations these effects will impart on MQMAS spectra recorded at low or moderate magnetic fields are thus evidenced.

NMR Spectroscopy of Phase Transitions in Minerals

Nuclear magnetic resonance (NMR) spectroscopy has been used extensively since the 1960’s to study phase transformations. When Lippmaa et al. (1980) presented the first significant high-resolution solid-state NMR spectroscopic study of minerals, the study of structural phase transitions by NMR was a mature field, appearing primarily in the physics literature (e.g., Blinc 1981; Rigamonti 1984). The sensitivity of NMR spectroscopy to short-range structure (first- and second-coordination spheres) and low-frequency dynamics (i.e., frequencies much lower than the thermal vibrations of atoms) make it useful for determining changes in the structure and dynamics of solids that occur near phase transitions. This combination of characteristic time- and distance-scales is not easily accessible by other techniques. Widely studied phase transformations include order-disorder and displacive transitions in compounds with perovskite, antifluorite, β-K2SO4 (A2BX4), KH2PO4 (“KDP”), and other structure types, including some mineral phases (e.g., colemanite; Theveneau and Papon 1976). These studies used primarily single-crystal techniques and were mostly limited to phases that exhibit high symmetry and possess one crystallographic site for the nucleus studied. In some cases, the NMR data can help distinguish order-disorder from purely displacive transition mechanisms. Also, careful measurement of NMR relaxation rates provides information on the spectral density at low frequencies, which reflects softening lattice vibrations or freezing-in of rotational disorder modes. Many phase transitions interesting to mineralogists became accessible to NMR spectroscopy in the late 1980’s with the commercial availability of magic-angle-spinning (MAS) NMR probe assemblies capable of operation at extended temperatures (up to about 600°C) and the development of high-temperature NMR capability at Stanford (Stebbins 1995b). These technical advances enabled many of the structural transitions that occur in minerals to be studied in situ by NMR, including those in phases for which large single crystals are not available. MAS-NMR …

Miscibility of poly(epichlorohydrin)/poly(vinyl acetate) blends investigated with high-resolution solid-state 13C NMR

The miscibility of poly(epichlorohydrin) (PECH)/poly(vinyl acetate) (PVAc) blends were investigated by differential scanning calorimeter and 13C cross polarization (CP) combined with magic angle spinning (MAS) spectroscopy. All the blends displayed single but increasing glass transition temperature with increased PVAc concentration. This indicates that the blend system is miscible on the scale of 10–30 nm for the entire composition. To examine the miscibility of the system on the scale below 10 nm, high-resolution solid-state 13C nuclear magnetic resonance experiment was carried out. The measurement of cross polarization rate between proton and 13C carbon nuclei ( T CH) showed that intermolecular cross polarization was slightly enhanced with increase of PECH composition. Single effective 1H spin–lattice relaxation ( T 1) time was found for PECH/PVAc. This observation suggests that interdomain spin–spin communications among all the protons in PECH/PVAc blends were possible on the scale of 10–30 nm, which is in good agreement with the DSC results. In the 1H rotating-frame spin–lattice relaxation ( T 1ρ) experiment, however, the blends displayed two-component exponential relaxation behavior, implying that interdomain spin–spin communications among all the protons were not possible within the time of 1H T 1ρ. Therefore, the domain size is estimated to be 3–30 nm in diameter.

Nuclear magnetic resonance spectroscopy of bone substitutes

Calcium phosphate bone replacement biomaterials are widely used in different applications. Structure, composition, and organization are, before implantation, analyzed with different methods. Among them, X-ray diffraction is a recognized test. As bioresorption produces more amorphous material, the process is observed and quantified via scanning electron microscopy. Comparatively high-resolution 31P solid-state nuclear magnetic resonance spectroscopy is able to analyze raw ceramics composition and to estimate osteoformation.

Evaluation of EVA-PVAc blend behavior by 1-D and 2-D solid-state NMR

Ethylene-co-vinyl acetate and poly(vinyl acetate) blends were prepared in different proportions by melting in a HAAKE Rheomix mixer. The blends were prepared at a fixed temperature, rotation rate, and processing time. High-resolution solid-state nuclear magnetic resonance was chosen to characterize the blends with respect to structure-mobility-compatibility employing magic angle spinning with cross polarization and high-power hydrogen decoupling and the measurements of the proton spin-lattice relaxation time in the rotating frame (T H 1 ρ). The miscibility between polymer chains was also studied by two-dimensional 1 H- 13 C shift correlation (HETCOR).

Evaluation of EVA–PVAc blend behavior by 1‐D and 2‐D solid‐state NMR

Ethylene-co-vinyl acetate and poly(vinyl acetate) blends were prepared in different proportions by melting in a HAAKE Rheomix mixer. The blends were prepared at a fixed temperature, rotation rate, and processing time. High-resolution solid-state nuclear magnetic resonance was chosen to characterize the blends with respect to structure–mobility–compatibility employing magic angle spinning with cross polarization and high-power hydrogen decoupling and the measurements of the proton spin–lattice relaxation time in the rotating frame (Tρ). The miscibility between polymer chains was also studied by two-dimensional 1H–13C shift correlation (HETCOR). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 221–226, 1999

Thermal characterization and solid-state13C-NMR investigation of blends of poly(N-phenyl-2-hydroxytrimethylene amine) and poly(N-vinyl pyrrolidone)

The miscibility and thermal properties of poly(N-phenyl-2-hydroxytrimethylene amine) [N(Ph)CH 2 CHOHCH 2 ] n /poly(N-vinyl pyrrolidone) (PHA/PVP) blends were examined by using differential scanning calorimetry (DSC), high-resolution solid-state nuclear magnetic resonance (NMR) techniques, and thermogravimetric analysis (TGA). It was found that PHA is miscible with PVP, as shown by the existence of a single composition-dependent glass transition temperature (T g ) in the whole composition range. The DSC results, together with the 13 C crosspolarization (CP)/magic angle spinning (MAS)/high-power dipolar decoupling (DD) spectra of the blends, revealed that there exist rather strong intermolecular interactions between PHA and PVP. The increase in hydrogen bonding and in T g of the blends was found to broaden the line width of CH-OH carbon resonance of PHA. The measurement of the relaxation time showed that the PHA/PVP blends are homogeneous at least on the scale of 1-2 nm. The proton spin-lattice relaxation in both the laboratory frame and the rotating frame were studied as a function of the blend composition, and it was found that blending did not appreciably affect the spectral densities of motion (sub-T g relaxation) in the mid-MHz and mid-KHz frequency ranges. Thermogravimetric analysis showed that PHA has rather good thermal stability, and the thermal stability of the blend can be further improved with increasing PVP content.

Molecular Design of Fluorocarbon Film Architecture by Pulsed Plasma Enhanced and Pyrolytic Chemical Vapor Deposition

Pulsed plasma enhanced chemical vapor deposition (pulsed PECVD) and pyrolytic chemical vapor deposition (pyrolyric CVD) of fluorocarbon films from hexafluoropropylene oxide (HFPO) have demonstrated the ability to molecularly design film architecture. Film structures ranging from highly amorphous crosslinked matrices to linear perfluoroalkyl chain crystallites can be established by reducing the modulation frequency of plasma discharge in plasma activated deposition and by eventually shifting mechanistically from an electrically activated to a thermally activated process. X-ray photoelectron spectroscopy (XPS) showed CF2 content increasing from 39–65 mol%. Fourier transform infrared spectroscopy (FTIR) showed an increasing resolution between the symmetric and asymmetric CF2 stretches, and a reduction in the intensity of the amorphous PTFE and CF3 bands. High-resolution solid-state 19F nuclear magnetic resonance spectroscopy (NMR) revealed an increasing CF2CF2CF2 character, with the pyrolytic CVD film much like bulk poly(tetrafluoroethylene) (PTFE). X-ray diffraction (XRD) patterns evidenced an increase in crystallinity, with the pyrolytic CVD film showing a characteristic peak at 2θ = 18° representing the (100) plane of the hexagonal structure of crystalline PTFE above 19°C.

Examination of miscibility at molecular level of poly(hydroxyether of bisphenol A)/poly(N-vinyl pyrrolidone) blends by cross-polarization/magic angle spinning13C nuclear magnetic resonance spectroscopy

The miscibility of poly(hydroxyether of bisphenol A) (phenoxy) and poly(N-vinyl pyrrolidone) (PVP) was investigated by differential scanning calorimetry (DSC) and high-resolution solid-state nuclear magnetic resonance (NMR) techniques. The DSC studies showed that the phenoxy/PVP blends have a single, composition-dependent glass transition temperature (Tg). The S-shaped Tg-composition curve of the phenoxy/PVP blends was reported, which is indicative of the strong intermolecular hydrogen-bonding interactions. To examine the miscibility of the system at molecular level, high-resolution solid-state 13C nuclear magnetic resonance (NMR) technique was employed. Upon adding phenoxy to system, the chemical shift of carbonyl carbon resonance of PVP was observed to shift downfield by 1.6 ppm in the 13C cross-polarization (CP)/magic angle spinning (MAS) together with the high-power dipolar decoupling (DD) spectra when the concentration of phenoxy is 90 wt %. The observation was responsible for the formation of intermolecular hydrogen bonding. The proton spin-lattice relaxation time T1(H) and the proton spin-lattice relaxation time in the rotating frame T1ρ(H) were measured as a function of the blend composition. The T1(H) result was in good agreement with the thermal analysis, i.e., the blends are completely homogeneous on the scale of 20 ∼ 30 nm. The six results of T1ρ(H) further indicated that the blends were homogeneous on the scale of 40 ∼ 50Å. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2291–2300, 1998

Miscibility, Intermolecular Interactions, and Thermal Behavior of Poly(hydroxy ether of Bisphenol A)/Poly(ethyl oxazoline) Blends

The miscibility, intermolecular interactions and thermal behavior of the poly(hydroxy ether of Bisphenol A) (Phenoxy)/poly(ethyl oxazoline) (PEOx) blends were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. Each composition of the Phenoxy/PEOx blends investigated displays a single glass transition temperature (Tg), which is intermediate between those of the pure components and regularly varies with blend composition. The results of FTIR showed that there are intermolecular interactions between the pendant hydroxyl groups of Phenoxy and the carbonyl groups of PEOx. Spin-lattice relaxation times in both the laboratory and the rotating frame determined by high-resolution solid state 13 C NMR spectroscopy reveal that the spin-diffusion among all protons in the blends averages out the whole relaxation process, suggesting that the blends are intimately mixed on the scale of 10-15 A.

High-resolution solid-state nuclear magnetic resonance study of the tetrapropylammonium template in a purely siliceous MFI-type zeolite

High-resolution solid-state nuclear magnetic resonance study of the tetrapropylammonium template in a purely siliceous MFI-type zeolite

High‐resolution solid‐state nuclear magnetic resonance study of the tetrapropylammonium template in a purely siliceous MFI‐type zeolite

High‐resolution solid‐state nuclear magnetic resonance study of the tetrapropylammonium template in a purely siliceous MFI‐type zeolite

Carbon-13 high resolution solid state NMR study of natural fibres obtained from sugar cane without treatment and their composites with EVA

Natural fibres from three distinct type of sugar cane without any specific treatment to remove the sugar, lignin and impurities and their composites with EVA, have been analysed by carbon-13 high-resolution solid state nuclear magnetic resonance (NMR). The NMR techniques used were cross-polarization magic angle spinning (CP/MAS); variable contact-time and proton spin-lattice relaxation time in the rotating frame (T 1 H ρ). From those measurements it was observed that the molecular mobility of chains along the fibres has a particular behaviour.

The compatibility study of polycarbonate-polyvinyl pyrrolidone blend using high-resolution solid-state nuclear magnetic resonance

The combining nuclear magnetic resonance techniques in the solid state permit the evaluation of the polymeric systems homogeneity. In the polycarbonate-poly(vinyl pyrrolidone) (PVP) blends, the response of proton spin-lattice relaxation time in the rotating frame was the determinant to obtain information on the transition when the quantity of PVP is close to 40% by weight and a better organization of amorphous phase was detected. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 449–453, 1998

Conformation of dentin phosphophoryn adsorbed on hydroxyapatite crystals.

Phosphophoryn, the major noncollagenous protein of dentin, was adsorbed on synthetic hydroxyapatite crystals and analyzed by high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. Binding of the protein was inhibited by acidic polypeptides, especially by a phosphorylated peptide. After phosphophoryn was incubated with the crystals, the crystals were collected and analyzed by 13C-cross-polarization magic-angle-spinning NMR. Several signals could be assigned to carbons of aspartic acids, taking advantage of the unique amino acid composition of this protein. Chemical shifts of signals of aspartic acids are known to reflect secondary structure of the polypeptide. The chemical shifts obtained from the phosphophoryn indicate that the secondary structure of this protein on the crystal was near to a beta-sheet structure. This result is consistent with the result for poly(Asp) adsorbed on the crystals. The beta-sheet-like structure enables phosphophoryn to extend on the crystal surface and to cover the surface with only a small number of the molecules, resulting in the high inhibitory effect of this protein on crystal growth.