Characterization of crosslinked starch materials with spectroscopic techniques

The structure, mobility, and properties of crosslinked starch materials of various compositions were investigated with FTIR and NMR spectroscopy, and relaxation time measurements were taken with cross‐polarization/magic‐angle‐spinning (CP–MAS) and magic‐angle‐spinning (MAS) spectroscopy. Characterization by Fourier transform infrared spectroscopy confirmed the crosslinking reaction. The CP–MAS and MAS spectra allowed the assignment of the principal ¹³C signals. The molecular mobility of these polysaccharides was analyzed in terms of the cross‐relaxation time between the protons and carbons, the ¹H spin–lattice relaxation time in the rotating frame, and the ¹H longitudinal spin–lattice relaxation time. Relaxation studies showed that increasing the crosslinking degree increased the amorphous content, and the material became rigid as an increasing number of covalent bonds in the polymer network reduced mobility. The values of the spin–lattice relaxation in the rotating frame reflected the homogeneous nature of the materials. The correlation between the crosslinking degree, structure, and mobility and the sorption properties of these sorbents was examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2650–2663, 2004     

Synthesis and characterization of novel polyureas based on benzimidazoline‐2‐one and benzimidazoline‐2‐thione hard segments

Six novel polyureas were prepared from benzimidazolin‐2‐one and benzimidazolin‐2‐thione, which acted as hard segments, with two aromatic diisocyanates (4,4′‐diphenylmethane diisocyanate and toluene 2,4‐diisocyanate) and one aliphatic diisocyanate (hexamethylene diisocyanate). The polymers that formed were fully characterized with Fourier transform infrared spectroscopy, ¹³C‐NMR cross‐polarization/magic‐angle spinning, differential scanning calorimetry, and thermogravimetry. X‐ray diffraction revealed that the polymers contained crystalline and amorphous regions that varied with the nature of the backbone structures. All the polyureas were insoluble in common organic solvents, and this made it difficult to investigate their solution properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 576–583, 2006     

Study on secondary structural transition of nano‐TiO2 modified silk fibroin composite films by two‐dimensional Raman correlation spectroscopy and solid‐state 13C‐NMR spectroscopy

By a sol–gel processing, the nano‐TiO₂/silk fibroin (SF) composite films were prepared. One‐dimensional (1D) Raman, two‐dimensional (2D) correlation Raman spectroscopy, and ¹³C cross‐polarization magic‐angle‐spinning nuclear magnetic resonance (¹³C CP‐MAS NMR) were used to characterize the structural evolution of SF as the nano‐TiO₂ content increased from 0 to 0.4 wt%. The experimental data demonstrated that the secondary structures in the pure SF film and nano‐TiO₂/silk fibroin (SF) composite films were random coil, α‐helix and β‐sheet structures. The nano‐TiO₂ particles formed in the SF films might induce partial structural transitions from random coil and Silk I (α‐helix) to Silk II (β‐sheet). The transition identified by 2D‐Raman correlation spectra was the following order: silk I‐like structure, silk I (α‐helical structure), Silk II‐like structure, and Silk II (β‐sheet structure). POLYM. COMPOS., 36:121–127, 2015. © 2014 Society of Plastics Engineers     

Solid state 19F NMR study of crystal transformation in PVDF and its nanocomposites

The polymorphism of poly(vinylidene fluoride) (PVDF) and its nanocomposites was studied by means of solid state nuclear magnetic resonance spectroscopy. ¹³C cross polarization magic angle spinning (¹³C CP MAS) NMR spectra were recorded using simultaneous high‐power decoupling on both the proton and fluorine channels. Both ¹H → ¹³C and ¹⁹F → ¹³C CP experiments were conducted, giving identical results apart from intensity variations due to the CP efficiency. Two main resonances for the CF₂ and the CH₂ groups were observed for both neat PVDF (PVDF‐C0) and the nanocomposite containing 2 wt% clay (PVDF‐C2) samples. ¹⁹F CP MAS spectra were obtained from long proton spin‐lock experiments with a shorter contact time. The results showed two strong resonances at ?84 and ?98 ppm with equal intensities, representing the α‐form crystalline structure of PVDF. It was shown that the clay induces the crystallization of PVDF in β‐form. Our earlier investigations using thermal analysis and X‐ray scattering methods also showed crystal transformation of PVDF in its clay nanocomposites. POLYM. ENG. SCI. 46:1684–1690, 2006. © 2006 Society of Plastics Engineers     

High‐resolution 13C–nuclear magnetic resonance study of heterogeneous amorphous polymers

The combination of solid‐state nuclear magnetic resonance (NMR) techniques is very helpful for examining the behavior of heterogeneous amorphous polymers. With the magic‐angle spinning (MAS) technique, employing special conditions, only the mobile fraction of the molecule can be assigned. Cross‐polarization magic‐angle spinning (CPMAS) permits the evaluation of changes in the NMR line shapes and chemical shifts. The employment of proton spin‐lattice relaxation times (T₁ and T₁ρ) gives useful information on the molecular dynamic in heterogeneous polymers. From these parameters the response of the molecular mobility behavior of the polymer chains can be obtained. The results of the present work are discussed in this article in terms of molecular mobility and domain formations of heterogeneous amorphous polymers in order to understand the relations in the structure–mobility property. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 473–476, 2003     

NMR study of poly(vinylpyrrolidone)/poly(ethylene oxide) blends

Development of polymeric blends has become very important for polymer industries because they have been shown to be successful and versatile alternatives to obtain new polymers. In this work binary blends formed by poly(vinylpyrrolidone) (PVP) and poly(ethylene oxide) (PEO) were studied by solution and solid‐state NMR to determine their physical interaction, homogeneity, and compatibility for use as membranes to separate water/alcohol. The NMR results allowed us to acquire information on the microstructure and molecular dynamic behavior of polymer blends. From the NMR solution it was possible to evaluate the microstructure: PVP presented a preferential syndiotactic distribution sequence and PEO presented two regions, one crystalline and the other amorphous. Considering the solid‐state NMR results it was possible to evaluate the molecular dynamics and all binary blends, showing that PEO behaves as a plasticizer; some intermolecular interaction was also observed. An important point was to evaluate the microstructure of the carbonyl PVP using cross polarization/magic‐angle spinning (CP/MAS) and CP/MAS/dipolar decoupling that was not observed before. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2820–2823, 2002     

Schiff base polymers derived from 2,5‐diformylfuran

Polymerization of 2,5‐diformylfuran with two primary amines was carried out in acetonitrile and ethanol at room temperature. The reaction was characterized using a combination of mass spectroscopy and NMR spectroscopy, which revealed the clean formation of the imine –CH?N? functional group. Although some cyclic products were detected from mass spectroscopy, the ring size was limited to products that have the ?CH?N? group only in anti‐geometry. The furan Schiff bases exhibit good thermal stability. While mass spectra evidenced oligomers of different lengths, cross‐polarization magic angle spinning ¹³C NMR spectra of the insoluble polymer revealed the linear structure as proposed. © 2013 Society of Chemical Industry     

13C‐NMR study on cure‐accelerated phenol‐formaldehyde resins with carbonates

Both liquid‐ and solid‐state carbon‐13–nuclear magnetic resonance (¹³C‐NMR) spectroscopies were used to investigate the cure acceleration effects of three carbonates (propylene carbonate, sodium carbonate, and potassium carbonate) on liquid and cured phenol‐formaldehyde (PF) resins. The liquid‐phase ¹³C‐NMR spectra showed that the cure acceleration mechanism in the propylene carbonate‐added PF resin seemed to be involved in increasing reactivity of the phenol rings, whereas the addition of both sodium carbonate and potassium carbonate into PF resin apparently resulted in the presence of ortho–ortho methylene linkages. Proton spin‐lattice rotating frame relaxation time (T_1ρH) measured by solid‐state ¹³C cross polarization/magic‐angle spinning NMR spectroscopy was smaller for the cure‐accelerated PF resins than that of the control PF resin. The result indicated that the cure‐accelerated PF resins are less rigid than the control PF resin. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1284–1293, 2000     

NMR a critical tool to study the production of carbon fiber from lignin

The structural changes occurring to hardwood Alcell™ lignin as a result of fiber devolatilization/extrusion, oxidative thermo-stabilization and carbonization are investigated in this study by solid-state and solution nuclear magnetic resonance (NMR) spectroscopy techniques. Solution based ¹H–¹³C correlation NMR of the un-spun Alcell™ lignin powder and extruded lignin fiber detected modest changes occurring due to fiber devolatilization/extrusion in the type and proportion of aliphatic side-chain carbons or monolignol inter-unit linkages. Molecular weight analysis by gel permeation chromatography (GPC), along with an additional ³¹P NMR method used to indicate changes in terminal hydroxyl functionality, suggest fiber devolatilization/extrusion causes both chain scission and condensation reactions. ¹H CRAMPS (combined rotation and multiple-pulse spectroscopy) and ¹³C cross-polarization/magic angle spinning (CP/MAS) spectra of extruded and stabilized lignin fibers indicate stabilization severely reduces the proportion of methoxy groups present, while also increasing the relative proportion of carbonyl and carboxyl-related structures, typically associated with cross-linking chemistries. ¹³C direct-polarization/magic angle spinning (DP/MAS) analysis of stabilized and carbonized fibers shows an increased relative amount of carbon–carbon bonds on aryl structures and a relative decrease of aryl ethers. DP/MAS dipolar dephasing experiments suggest that a majority of non-protonated carbons convert from carbonyl to aryl and condensed aryl structures during carbonization.     

Regioselective substitution of 2‐isocyanatoethylmethacrylate onto cellulose

Cellulose is a well‐known versatile polymer that presents a wide range of material properties via the substitution and grafting reactions of its hydroxyl groups. Because of their commercial potential, combinations of cellulose and vinyl polymers have been examined with various grafting methods. In this study, the condensation reactions of regioselective and nonregioselective substitution with 2‐isocyanatoethylmethacrylate were performed in a homogeneous solvent system of dimethyl acetamide/lithium chloride. The successful substitution was confirmed by Fourier transform infrared spectroscopy, ¹H‐NMR, cross‐polarization/magic angle spinning ¹³C‐NMR, thermogravimetric analysis, and X‐ray diffraction. The substituted celluloses showed excellent thermal stability and a different polymorph with a depressed cellulose–intrinsic polymorphic phase. The 2‐isocyanatoethylmethacrylate side chain seemed to expand the intermolecular distance with enhanced chain mobility and trigger the formation of a novel crystalline polymorph with a dramatically improved thermal stability. This investigation provided us with a useful understanding of the modification of cellulose with spatial distribution control for advanced future applications requiring a combination of cellulose with vinyl polymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis of a novel linear water‐soluble β‐cyclodextrin polymer

A novel linear water‐soluble β‐cyclodextrin polymer has been prepared by grafting β‐cyclodextrin on poly[(methyl vinyl ether)‐alt‐(maleic anhydride)]. First, lithium hydride was used to obtain the mono‐alkoxide β‐CD. Grafting of β‐CD derivatives to the polymer backbone was then carried out by an esterification method. Using this method, polymers containing various amounts of β‐CD were synthesized. The resulting grafted polymers were characterized by two complementary methods, ¹H NMR and IR spectroscopy. The first was used to calculate the degree of substitution for the low amounts of β‐CD. The second method was very useful to evaluate the degree of substitution and the molar ratio of CD especially for high amounts of grafting. Our results indicate good agreement between both methods for intermediate rates. Copyright © 2004 Society of Chemical Industry     

Structural characterization of nylon 4 in the solid state by high-resolution solid-state H NMR spectroscopy

High-resolution solid-state ¹H NMR spectra of nylon 4 melt-quenched sample and single crystal sample in the solid state were measured in a wide range of temperatures from room temperature to 505 K by using solid state 300 MHz NMR with the FSLG-2 homo-nuclear dipolar decoupling method combined with high speed magic angle spinning method. From the experimental results, structural characterization on the crystalline and non-crystalline components was carried out. Further, intermolecular interaction between nylon 4 and water contained in the sample was discussed.     

Detection of lead ion binding on bifunctional chelating/ion‐exchange resins by cross‐polarization/magic‐angle spinning solid‐state nuclear magnetic resonance

Solid‐state nuclear magnetic resonance (S‐NMR) can reveal much useful information, including conformations, stereoregularity, defect structures, and comonomer sequence. S‐NMR is especially useful for revealing microstructural differences that can alter local polymer chains. A series of bifunctional chelating/ion‐exchange resins, containing differing ratios of iminodiacetic acid to acetic acid, were synthesized. Cross‐polarization magic‐angle spinning (CP/MAS) ¹³C‐NMR was employed to measure conformation changes both before and after the bonding of ligands and lead ion adsorbed on bifunctional chelated/ion‐exchange resins in this investigation. From the ¹³C‐NMR spectra, as the lead ion was adsorbed by the iminodiacetic acid chelating group, the motion of molecular chain would be inhibited and the resonance peaks of the carboxylate anion at 170 ppm would shift downfield. Compared to the FTIR results, the downfield shift of the resonance peaks indicated that the bonding of carboxylate anion and lead ion adsorbed displayed an ionic trend. Furthermore, the bonding of the carboxylic group and lead ion adsorbed changed from ionic to covalent as the chelating group in bifunctional/ion‐exchange resins decreased. The linear relationship between the areas of those resonance peaks and the amount of lead ion adsorbed was obtained from the spectra fitting. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 919–928, 2002     

Radiation degradation of epoxidized natural rubber studied by solid‐state nuclear magnetic resonance and infrared spectroscopy

The mechanism of radiation‐induced structural changes in epoxidized natural rubber was investigated using nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. Samples were irradiated both under vacuum and in air. Because the rubbers crosslinked during irradiation, solid‐state NMR had to be used. The cross polarized/magic angle spinning NMR spectra were used to calculate the radiation yields. Ring opening of the epoxy groups was found to occur during irradiation. Most of the crosslinking was due to epoxy group ring opening, and very little or no C C crosslinking was observed. © 2000 Society of Chemical Industry     

Tunable luminescence from bismuth‐doped phosphate laser glass by engineering photonic glass structure

Because of ultra‐broadband near‐infrared (NIR) emission bismuth‐activated glasses and fibers offer a new promising platform for novel photonic devices such as new type of optical amplifiers and broadly tunable fiber lasers. Yet, challenge remains to manipulate the NIR emission behavior of bismuth (Bi) in photonic glasses for efficient Bismuth‐doped fiber and fiber lasers. Here, by engineering phosphorus and aluminum's topology, broadly tunable NIR emission has been realized in Bismuth‐doped phosphate laser glass. Structural and optical analyses on ²⁷Al magic‐angle spinning nuclear magnetic resonance (MAS NMR), ³¹P MAS NMR, fourier transform infrared (FTIR) and static emission spectra suggest that polymerization of glass network can be improved by proper addition of aluminum into the system, which can be evidenced by partial conversion of Q² to Q³ species of phosphorus and the shift of P–O–P asymmetric stretching vibration toward lower frequency, and this turns out beneficial to Bi NIR emission. Embedding aluminum tetrahedra into phosphorus glass network can reduce the local crystal field around bismuth and therefore lead to the blueshift of Bi emission. This work presents new insights into the luminescent behavior of Bi ions in phosphate glass and it helps the design and fabrication of Bismuth‐doped glasses and fibers in future.     

NMR characterisation of dicyclopentadiene resins and polydicyclopentadienes

Dicyclopentadiene (DCPD) thermosetting resin has been characterized by nuclear magnetic resonance (NMR) technique. The main monomer in DCPD resin is found to be in endo isomer form. Solid-state ¹³C cross polarization/magic angle spinning and ¹³C high-power decoupling NMR techniques have been applied for characterization of polymer network during curing and after cure. NMR spectra of carbon atoms in rigid phase and in mobile phase have been investigated. The possibility of three structural elements in polymer network was discussed. Solid-state NMR technique was applied to study of poly-DCPD oxidation. © 1996 John Wiley & Sons, Inc.     

Study of nylon 6 and poly(propylene oxide) blends by thermal measurements and carbon-13 NMR high resolution solid-state

Samples of Nylon 6/poly(propylene oxide), with poly(propylene oxide) (PPO) content varying up to 35%, have been examined using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR) carbon-13 at solid-state. Carbon-13 spectra were measured by cross-polarization (CP), magic angle spinning (MAS), and high-power hydrogen decoupling (HPHD). The variation contact time experiment and MAS technique were also determined. The data are discussed in terms of compatibility and plasticization of the samples. © 1995 John Wiley & Sons, Inc.     

Preparation and solid‐state nuclear magnetic resonance characterization a styrene/butadiene/acrylonitrile (ABS)/poly(vinyl chloride) (PVC)/gypsum ternary system

Polymer blends were prepared to obtain a new material with specific characteristics. To prepare a miscible polymer blend, it is necessary to evaluate the chemical structure and molecular dynamics of all polymers involved and to thereby establish a structure–property relationship for these materials. In this work, ternary blends for application in plates chromatography were formed with styrene/butadiene/acrylinotrile (ABS), poly(vinyl chloride) (PVC), and gypsum, and were studied by solid‐state carbon‐13 nuclear magnetic resonance (¹³C NMR). Magic‐angle spinning (MAS), cross‐polarization magic‐angle spinning (CPMAS), variable contact time (VCT), and proton spin‐lattice relation time in the rotating frame (Tρ) were the techniques used to evaluate the miscibility, homogeneity, and compatibility of polymer blends at the molecular level. From the values of Tρ, it was verified that ABS/PVC/gypsum formed good polymer blends with some specific physical interaction at the molecular level. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 293–296, 2003     

Solid‐state carbon‐13 NMR study of material composites based on sugarcane bagasse and thermoplastics polymers

The composites formed by sugarcane bagasse and thermoplastic polymers, such as polypropylene (PP), polyethylene (PE), and ethylene‐co‐vinyl acetate (EVA), have been analysed by carbon‐13 high‐resolution solid‐state nuclear magnetic resonance (NMR), employing crosspolarization magic angle spinning (CPMAS); variable contact‐time experiment and proton spin‐lattice relaxation time in the rotating frame. NMR responses showed that these techniques can be used to observe the degree of compatibility and homogeneity of different polymers composites. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2150–2154, 2001