The Experts below are selected from a list of 120 Experts worldwide ranked by ideXlab platform

Fumitaka Horii - One of the best experts on this subject based on the ideXlab platform.

  • Solid-State ^13C NMR Studies of the Structure and Chain Conformation of Thermotropic Liquid Crystalline Polyether Crystallized from the Liquid Crystalline Glassy Phase
    Polymer Journal, 2004
    Co-Authors: Miwa Murakami, Hironori Kaji, Hiroyuki Ishida, Fumitaka Horii
    Abstract:

    The structure and chain conformation of the form β sample newly crystallized from the liquid crystalline (LC) glassy phase have been investigated for a main-chain thermotropic LC polyether, which was polymerized from 3,3′-dimethyl-4,4′-hydroxyl-biphenyl and 1,10-dibromodecane, by solid-state ^13C NMR spectroscopy. The ^13C spin–lattice relaxation analyses reveal that there exist two components with different T _1C values, which correspond to the crystalline and Noncrystalline (supercooled liquid crystalline) components. By employing such differences in T _1C, the spectra of the respective components are separately recorded, and the conformations of their CH_2 sequences are evaluated by considering the γ- gauche effect on the ^13C chemical shifts. As a result, the crystalline component is found to adopt the t ′ xxxtxxxt ′ conformation whereas another conformation of t ′ xxxxxxxt ′ is preferably induced in the Noncrystalline Region, where t , t ′, and x indicate trans , trans -rich and trans – gauche exchange conformations, respectively. These conformations are markedly different from txtxtxtxt and xxxxxxxxx in the corresponding components for the form α sample previously reported, probably reflecting the difference in crystallization from different nematic phases N_α and N_β. Moreover, molecular motion for the mesogen units and the spacer CH_2 sequences has been examined by the chemical shift anisotropy (CSA) analysis based on the magic angle turning (MAT) method. The mesogenic phenylene carbons are found to undergo rather restricted flip motion with amplitudes less than 30° around the bond axis in both crystalline and Noncrystalline Regions, while the flip rates associated with the ^13C spin–lattice relaxation may be greatly different in the two Regions. The CSA spectrum of the spacer CH_2 carbons significantly narrows possibly as a result of the specific change in chain conformation in the crystalline and Noncrystalline Regions.

  • Solid‐state NMR analyses of the crystalline–Noncrystalline structure and its thermal changes for ethylene ionomers
    Journal of Polymer Science Part B, 2002
    Co-Authors: Kazuhiro Kuwabara, Fumitaka Horii
    Abstract:

    The crystalline–Noncrystalline structure and its structural changes from thermal treatments for ethylene ionomers have been investigated with solid-state 13C and 23Na NMR spectroscopy. 13C spin–lattice relaxation time (T1C) measurements reveal that as-received ethylene ionomers have much enhanced molecular mobility in the crystalline Region in comparison with conventional polyethylene samples. By appropriate annealing, however, polyethylene-like morphological features reflecting T1C behavior can also be observed. 13C spin–spin relaxation time (T2C) measurements for the Noncrystalline Region reveal the existence of two components with different T2C values, and these two components have been assigned to the crystalline–amorphous interfacial and rubbery–amorphous components. These results indicate that the structure of the major part of the Noncrystalline Region in the ethylene ionomers is similar to that of bulk-crystallized polyethylene samples, regardless of possible ionic aggregates. The origin of the lower temperature endothermic peak in the heating process of the differential scanning calorimetry curve observed for the as-received sample has also been examined somewhat in detail. As a result, it is proposed that the melting of smaller crystallites produced during storage at room temperature is the origin of the lower temperature peak. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1142–1153, 2002

  • Solid-State ^13C NMR and ^1H CRAMPS Investigations of the Hydration Process and Hydrogen Bonding for Poly(vinyl alcohol) Films
    Polymer Journal, 2001
    Co-Authors: Kenji Masuda, Hironori Kaji, Fumitaka Horii
    Abstract:

    The hydration process and resulting hydrogen bonding for atactic poly(vinyl alcohol) (A-PVA) films have been investigated by high-resolution solid-state NMR spectroscopy. In ^1H CRAMPS spectra for the A-PVA films which are dried after soaked in deuterated water for different periods, the prominent decrease in intensity is observed within 5 min for the resonance line assigned to the intermolecular hydrogen-bonded OH (OH_inter) groups while such an intensity reduction occurs over about 30 min for the line ascribed to the intramolecular hydrogen bonded-OH (OH_intra) groups. This fact indicates that the exchange between the OH protons and deuteriums of deuterated water is more preferably induced for the OH_inter groups compared to the case of the OH_intra groups in the Noncrystalline Region. In contrast, all OH protons in the crystalline Region, including OH protons free from hydrogen bonding that are selectively allowed to exist in this Region, are found to undergo the exchange with deuteriums at a much slower rate. It is also found by the ^13C spin-lattice relaxation analysis that there exist three components with different T _1C values assigned to the crystalline, less mobile, and mobile components in the A-PVA films with the water content of 0.82 g-water/g-PVA. The line shape analysis of the CH resonance line for the crystalline component reveals that the probability of the formation of intramolecular hydrogen bond in the meso sequence significantly increases by the addition of water. In the less mobile component the intra- and intermolecular hydrogen bonds are still kept irrespective of the enhanced molecular motion induced by the hydration but the gauche conformation markedly increases in mole fraction probably as a result of partial breaking of hydrogen bonding. In contrast, the mobile component is subjected to rapid exchanges among different conformations and hydrogen bonds, resulting in the appearance of the sharp triplet assignable to the CH carbons in the mm , mr , and rr sequences like the spectrum in solution. Finally the size of the crystallites is estimated to be about 26 nm by the analysis of the ^1H spin diffusion process from the water-swollen Noncrystalline Region to the crystalline Region.

  • Studies on Different types of hydrogen bonds in poly(vinyl alcohol) films by 1H CRAMPS and solid-state two-dimensional 1H-13C heteronuclear correlation analyses
    Polymer Journal, 2001
    Co-Authors: Kenji Masuda, Hironori Kaji, Fumitaka Horii
    Abstract:

    Different hydrogen-bonded states of OH groups in poly(vinyl alcohol) (PVA) films with different tacticities have been characterized by 1H combined rotation and multiple pulse spectroscopy (CRAMPS), solid-state 13C NMR and two-dimensional (2D) 1H-13C heteronuclear correlation (HETCOR) analyses. The newly developed line shape analysis for the 1H CRAMPS spectra reveals the existence of three types of OH groups in different hydrogen-bonded states below Tg; intramolecular and intermolecular hydrogen bonded OH (OHintra, OHinter) groups and OH (OHf) groups free from hydrogen bonding. Above Tg, another resonance line which can be assigned to highly mobile OH (OHr) groups in the Noncrystalline Region appears as a result of the reduction in mole fractions of the OHintra and OHinter groups, in good accord with the confirmation of the rubbery component by the solid-state 13C NMR line shape analysis. In contrast, the mole fraction of the OHf groups stays constant at −60-160°C, indicating that these OH groups are preferentially distributed in the crystalline Region. In order to examine the correlations of the results obtained by 1H CRAMPS and solid-state 13C NMR analyses, 2D 1H-13C HETCOR spectra have been also measured at room temperature for atactic and main-chain deuterated atactic PVA films. As a result, evident correlations between 1H OH and 13C CH constituent lines are observed at a cross polarization (CP) contact time of 120 μs, indicating the validity of the assignments for the 1H OH and 13C CH resonance lines made previously as well as in this work.

  • Studies on Different Types of Hydrogen Bonds in Poly(vinyl alcohol) Films by ^1H CRAMPS and Solid-State Two-Dimensional ^1H-^13C Heteronuclear Correlation Analyses
    Polymer Journal, 2001
    Co-Authors: Kenji Masuda, Hironori Kaji, Fumitaka Horii
    Abstract:

    Different hydrogen-bonded states of OH groups in poly(vinyl alcohol) (PVA) films with different tacticities have been characterized by ^1H combined rotation and multiple pulse spectroscopy (CRAMPS), solid-state ^13C NMR and two-dimensional (2D) ^1H-^13C heteronuclear correlation (HETCOR) analyses. The newly developed line shape analysis for the ^1H CRAMPS spectra reveals the existence of three types of OH groups in different hydrogen-bonded states below T _g; intramolecular and intermolecular hydrogen bonded OH (OH_intra, OH_inter) groups and OH (OH_f) groups free from hydrogen bonding. Above T _g, another resonance line which can be assigned to highly mobile OH (OH_r) groups in the Noncrystalline Region appears as a result of the reduction in mole fractions of the OH_intra and OH_inter groups, in good accord with the confirmation of the rubbery component by the solid-state ^13C NMR line shape analysis. In contrast, the mole fraction of the OH_f groups stays constant at −60-160°C, indicating that these OH groups are preferentially distributed in the crystalline Region. In order to examine the correlations of the results obtained by ^1H CRAMPS and solid-state ^13C NMR analyses, 2D ^1H-^13C HETCOR spectra have been also measured at room temperature for atactic and main-chain deuterated atactic PVA films. As a result, evident correlations between ^1H OH and ^13C CH constituent lines are observed at a cross polarization (CP) contact time of 120 μs, indicating the validity of the assignments for the ^1H OH and ^13C CH resonance lines made previously as well as in this work.

Sanjay Rastogi - One of the best experts on this subject based on the ideXlab platform.

  • chain packing in the Noncrystalline Region of deuterated uhmwpe a solid state h 2 and c 13 nmr study
    European Polymer Journal, 2017
    Co-Authors: Ran Zhang, Guang Yang, Ting Xiao, Robert Graf, Ele Deboer, Rene Verhoef, A P M Kentgens, Sanjay Rastogi
    Abstract:

    Abstract Chain packing in the non-crystalline Region of a semi-crystalline polymer is strongly influenced by the crystallization conditions. Using a single-site catalytic system, deuterated Ultra High Molecular Weight Polyethylenes (UHMW-PEs) are synthesized and the chain topology of the Noncrystalline Region is investigated by solid-state NMR. The variability in chain packing within the Noncrystalline Region is introduced on crystallizing the same polymer either by controlled synthesis or solution or melt. 2H NMR combined with line shape simulations yield detailed information on the geometry and frequency of the segmental motion in the Noncrystalline Regions of deuterated UHMWPE crystallized at three different conditions. High resolution solid-state 13C NMR reveals the temperature dependence of the conformation statistics of chain segments in the Noncrystalline Regions of the samples. Combining the observations from the 2H and 13C NMR, the influence of segmental motions on the conformation statistics in the Noncrystalline Regions of the samples are discussed.

  • Correlation between Thermal and Mechanical Response of Nascent Semicrystalline UHMWPEs
    Macromolecules, 2017
    Co-Authors: Dario Romano, Niek Tops, Sanjay Rastogi
    Abstract:

    In spite of the abstract nature, entanglements are the folklore of polymer science, and their presence is realized in the semicrystalline and amorphous solid state as well as in the molten state (melt) of polymers. For example, the entangled state in the Noncrystalline Region is known to be the determining factor in melting kinetics and also in uniaxial as well as biaxial deformation of linear ultrahigh molecular weight polyethylenes (UHMWPEs). In this paper we aim to investigate a possible correlation between the melting of crystals and the ease of deformation of the semicrystalline polymer. Considering that the entanglement density, and the associated topological constraints residing in the Noncrystalline Region, can be influenced by the polymerization conditions, a series of UHMWPEs have been synthesized. For a set of polymers synthesized at fixed pressure, the characteristic melting time of the as-synthesized nascent crystals (τ1) measured by temperature-modulated DSC (TM-DSC) is found to decrease wit...

Guang Yang - One of the best experts on this subject based on the ideXlab platform.

  • chain packing in the Noncrystalline Region of deuterated uhmwpe a solid state h 2 and c 13 nmr study
    European Polymer Journal, 2017
    Co-Authors: Ran Zhang, Guang Yang, Ting Xiao, Robert Graf, Ele Deboer, Rene Verhoef, A P M Kentgens, Sanjay Rastogi
    Abstract:

    Abstract Chain packing in the non-crystalline Region of a semi-crystalline polymer is strongly influenced by the crystallization conditions. Using a single-site catalytic system, deuterated Ultra High Molecular Weight Polyethylenes (UHMW-PEs) are synthesized and the chain topology of the Noncrystalline Region is investigated by solid-state NMR. The variability in chain packing within the Noncrystalline Region is introduced on crystallizing the same polymer either by controlled synthesis or solution or melt. 2H NMR combined with line shape simulations yield detailed information on the geometry and frequency of the segmental motion in the Noncrystalline Regions of deuterated UHMWPE crystallized at three different conditions. High resolution solid-state 13C NMR reveals the temperature dependence of the conformation statistics of chain segments in the Noncrystalline Regions of the samples. Combining the observations from the 2H and 13C NMR, the influence of segmental motions on the conformation statistics in the Noncrystalline Regions of the samples are discussed.

  • Studies on the phase structure of ethylene‐vinyl acetate copolymers by solid‐state 1H and 13C NMR
    Journal of Polymer Science Part B, 2002
    Co-Authors: Qiujin Zhang, Guang Yang, Qun Chen
    Abstract:

    The phase structure of a series of ethylene-vinyl acetate copolymers has been investigated by solid-state wide-line 1H NMR and solid-state high-resolution 13C 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 13C NMR spin–lattice relaxation behavior was observed for the crystalline Region of all samples. The component with longer 13C NMR spin–lattice relaxation time (T1) was attributed to the internal part of the crystalline Region, whereas the component with shorter 13C NMR T1 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 13C NMR spin–lattice relaxation behavior is closely related to the crystalline structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2199–2207, 2002

  • solid state nmr study on the structure and mobility of the Noncrystalline Region of poly 3 hydroxybutyrate and poly 3 hydroxybutyrate co 3 hydroxyvalerate
    Polymer, 2002
    Co-Authors: Yan Chen, Guang Yang, Qun Chen
    Abstract:

    Abstract The Noncrystalline structures of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV) copolymers were studied by variable temperature solid-state wide-line 1 H NMR and solid-state high-resolution 13 C NMR spectroscopy. It is found that at room temperature there exists a rich and rigid component in the Noncrystalline Region of PHB and PHBV. The content of this component decreases with the increase in 3-hydroxyvalerate content in PHBV and with the increase in temperature. The brittleness of PHB may be partly attributed to the rigidness of the Noncrystalline Region at room temperature, while the improvement of the properties of PHBV may come from the enhanced mobility of the Noncrystalline Region.

Qun Chen - One of the best experts on this subject based on the ideXlab platform.

  • Studies on the phase structure of ethylene‐vinyl acetate copolymers by solid‐state 1H and 13C NMR
    Journal of Polymer Science Part B, 2002
    Co-Authors: Qiujin Zhang, Guang Yang, Qun Chen
    Abstract:

    The phase structure of a series of ethylene-vinyl acetate copolymers has been investigated by solid-state wide-line 1H NMR and solid-state high-resolution 13C 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 13C NMR spin–lattice relaxation behavior was observed for the crystalline Region of all samples. The component with longer 13C NMR spin–lattice relaxation time (T1) was attributed to the internal part of the crystalline Region, whereas the component with shorter 13C NMR T1 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 13C NMR spin–lattice relaxation behavior is closely related to the crystalline structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2199–2207, 2002

  • solid state nmr study on the structure and mobility of the Noncrystalline Region of poly 3 hydroxybutyrate and poly 3 hydroxybutyrate co 3 hydroxyvalerate
    Polymer, 2002
    Co-Authors: Yan Chen, Guang Yang, Qun Chen
    Abstract:

    Abstract The Noncrystalline structures of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV) copolymers were studied by variable temperature solid-state wide-line 1 H NMR and solid-state high-resolution 13 C NMR spectroscopy. It is found that at room temperature there exists a rich and rigid component in the Noncrystalline Region of PHB and PHBV. The content of this component decreases with the increase in 3-hydroxyvalerate content in PHBV and with the increase in temperature. The brittleness of PHB may be partly attributed to the rigidness of the Noncrystalline Region at room temperature, while the improvement of the properties of PHBV may come from the enhanced mobility of the Noncrystalline Region.

  • Dynamic study of the Noncrystalline phase of 13C-labeled polyethylene by variable-temperature 13C CP/MAS NMR spectroscopy
    Journal of Polymer Science Part B, 1992
    Co-Authors: Qun Chen, Takeyoshi Yamada, Hiromichi Kurosu, Isao Ando, Takeshi Shiono
    Abstract:

    The 13C spin-lattice relaxation times T1 of 13C-labeled polyethylene crystallized under different conditions were measured at temperatures from −120 to 44°C by variable-temperature solid-state high-resolution 13C nuclear magnetic resonance (NMR) spectroscopy, in order to determine accurately the dynamics of the Noncrystalline Region of the polymer. From these results, it was found that the T1 minimum for the CH2 carbons in the Noncrystalline Region of solution-crystallized polyethylene with high crystallinity appears at higher temperature by about 20°C than that of melt-quenched polyethylene with low crystallinity. This means that the molecular motion of the CH2 carbons in the Noncrystalline Regions is more constrained at a given temperature in the material of higher crystallinity. Furthermore, dynamics of the Noncrystalline Region is discussed in terms of the 13C dipolar dephasing times.

A K Rana - One of the best experts on this subject based on the ideXlab platform.

  • thermal behavior of vinyl ester resin matrix composites reinforced with alkali treated jute fibers
    Journal of Applied Polymer Science, 2004
    Co-Authors: Bijit Kumar Sarkar, R K Basak, A K Rana
    Abstract:

    The thermal behavior of vinyl ester resin matrix composites reinforced with jute fibers treated for 2, 4, 6, and 8 h with 5% NaOH was studied with Thermo-gravimetric analysis and differential scanning calorimetry. The moisture desorption peak shifted to a higher temperature, from 37 to 58.3°C, for all the treated-fiber composites because of improved wetting of the fibers by the resin and stronger bonding at the interface. The degradation temperature of the vinyl ester resin in the composites was lowered to 410.3°C from that of the neat resin, 418.8°C. The X-ray diffraction studies showed increased crystallinity of the treated fibers, which affected the enthalpy of the α-cellulose and hemicellulose degradation. The hemicellulose degradation temperature remained the same (299.7°C) in all the treated-fiber composites, but the enthalpy associated with the hemicellulose degradation showed an increasing trend in the treated composites with a small increase in the weight loss. This could be attributed to the increased hydrogen bonding between the more accessible OH groups of the hemicellulose in the Noncrystalline Region of the jute fiber and the resin. The degradation temperature of α-cellulose was lowered from 364.2 to 356.8°C in the treated composites. The enthalpy of α-cellulose degradation showed a decreasing trend with a lowering of the weight loss. The crystalline Regions of the fiber, consisting of closely packed α-cellulose chains, were bonded with the resin mainly on the surface through hydrogen bonds and became more resistant to thermal degradation; this reduced the weight loss. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 123–129, 2004

  • Thermal behavior of vinyl ester resin matrix composites reinforced with alkali‐treated jute fibers
    Journal of Applied Polymer Science, 2004
    Co-Authors: Bijit Kumar Sarkar, R K Basak, A K Rana
    Abstract:

    The thermal behavior of vinyl ester resin matrix composites reinforced with jute fibers treated for 2, 4, 6, and 8 h with 5% NaOH was studied with Thermo-gravimetric analysis and differential scanning calorimetry. The moisture desorption peak shifted to a higher temperature, from 37 to 58.3°C, for all the treated-fiber composites because of improved wetting of the fibers by the resin and stronger bonding at the interface. The degradation temperature of the vinyl ester resin in the composites was lowered to 410.3°C from that of the neat resin, 418.8°C. The X-ray diffraction studies showed increased crystallinity of the treated fibers, which affected the enthalpy of the α-cellulose and hemicellulose degradation. The hemicellulose degradation temperature remained the same (299.7°C) in all the treated-fiber composites, but the enthalpy associated with the hemicellulose degradation showed an increasing trend in the treated composites with a small increase in the weight loss. This could be attributed to the increased hydrogen bonding between the more accessible OH groups of the hemicellulose in the Noncrystalline Region of the jute fiber and the resin. The degradation temperature of α-cellulose was lowered from 364.2 to 356.8°C in the treated composites. The enthalpy of α-cellulose degradation showed a decreasing trend with a lowering of the weight loss. The crystalline Regions of the fiber, consisting of closely packed α-cellulose chains, were bonded with the resin mainly on the surface through hydrogen bonds and became more resistant to thermal degradation; this reduced the weight loss. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 123–129, 2004