Synthesis and solid state 13C-NMR studies of some cellulose derivatives

Several cellulose derivatives were synthesized and characterized by IR and ¹H-NMR spectroscopy. The positions of substitution in these derivatives were confirmed using solid state ¹³C-NMR spectroscopy techniques.     

A solid state 13C-NMR study of diamonds and graphites

The ¹³C-NMR spectra of gem quality and industrial diamonds show two resonances with the more intense resonance at high field. Two resonances are also shown in ¹³C-NMR spectra of various graphites; however, the low field resonance is of greater intensity than the high field resonance in the graphites. The resonances are very broad and they are assigned to graphite type (sp²) carbon and diamond type (sp³) carbon.     

13C-NMR spectral studies on the distribution of substituents in some cellulose derivatives

¹³C-NMR spectra of trityl cellulose (Tr-Cell), tosyl cellulose (Ts-Cell), cellulose S-methyl xanthate (Cell-M-Xan), and cellulose formate (CF) in dimethylsulfoxide-d₆ were analyzed at 50.4 MHz. It was found that the distribution of substituents in the anhydroglucose units of these cellulose derivatives can be estimated from their ring carbon spectra. The results showed that (i) in Tr-Cell having degree of substitution (DS) lower than 1, the hydroxyl groups at C-6 carbon position are selectively tritylated, (ii) in the case of Ts-Cell, the difference in the relative DS value among three different types of hydroxyl groups is not large, although the relative reactivities of hydroxyl groups toward tosylation decrease in the order C-6 > C-2 > C-3, (iii) in Cell-M-Xan, the hydroxyl groups at C-3 carbon position are mainly substituted, and (iv) the ease of formylation is C-6 > C-2 > C-3. The 100.8 MHz ¹³C-NMR spectra of O-methyl cellulose (MC) revealed that the reactivity order in commercial MC prepared from alkali cellulose is C-6 ? C-2 > C-3. Concerning MC, its water solubility was also discussed in terms of the distribution of substituents along the cellulose chain.     

Solution and solid state13C-NMR of barley straw lignins

Grass lignins are formed by the polymerization of phenoxy radicals and contain a variety of carbon-carbon and carbon-oxygen bonds. They are similar to the hardwood lignins, but differ by containing a substantial proportion of esterified cinnamic acids. Detailed nuclear magnetic resonance studies in conjunction with chemical analysis have given new information on the structure of grass lignins. Milled straw lignins (MSL) from barley were examined by both solution and solid-state (CP/MAS) NMR before and after acetylation. The assignment of the carbon-13 (100 MHz) solution spectra was achieved using model compound data, nuclear Overhauser enhancement (NOE) suppression, and insensitive nuclei enhanced by polarization transfer (INEPT) techniques. The NOE suppression permitted quantitative analysis of lignin, giving information on the ratio of specific carbon atoms. Use of the relaxation agent, chromium acetylacetonate, enabled accumulation of sufficient spectral data to give a spectrum suitable for integration after 90 h. The INEPT technique, which had not previously been used for lignin analysis, was successfully applied to acetylated MSL. This technique increased signal intensities 3–4-fold and simplified the spectrum by inverting methylene carbons and eliminating or inverting quaternary carbons. Comparison of this spectrum with the normal spectrum permitted accurate assignment of quaternary and methine carbons. The solid-state carbon-13 CP/MAS NMR was used to examinein situ lignin and the isolated MSL. The¹³C-CP/MAS spectrum ofin situ lignin shows that cellulose and hemicellulose resonances dominate with little evidence ot the aromatic structure of lignin. the¹³C-CP/MAS of MSL shows reduced carbohydrate resonances and increased aromatic resonances. The extent of modification to the barley straw was estimated and results indicate the presence oflignin-carbohydrate complexes. Detailed information on the nature of the linkages between lignin components and between lignin and carbohydrate components has been obtained from these spectra.     

The 13C-NMR solid state spectroscopy of various classes of coals

The ¹³C-NMR spectra of various classes of coal obtained in the solid state show two resonances, one of which is assigned to aromatic carbon and the other to aliphatic carbon. The resonances are very broad with the high field resonance centered at about 7 ppm below tetramethylsilane and a low field resonance centered at about 140 ppm below tetramethysilane. Based on our previous solid state ¹³C-NMR studies of graphite and diamond, the high field resonance is typical of a sp³ carbon whereas the low fields resonance is assigned to a sp² carbon whereas the low fields resonance is assigned to a sp² carbon. It is found that the antracitic coals have more aromatic (sp²) carbons than the bituminous, subbituminous and lignite coals. The analytical implications of this technique are briefly discussed.     

13C-NMR of ABS in the solid state. Characterization and relaxation studies

¹³C-NMR spectra of bulk acrylonitrile-butadiene-styrene (ABS) resin are reported. The styrene-co-acrylonitrile (SAN) carbons can be observed selectively by using high-power proton decoupling, cross polarization, and magic angle spinning (MAS). The polybutadiene (PBd) carbons can be observed selectively by using low-power proton decoupling, with or without MAS. Methods and conditions for using ¹³C-NMR to quantify the amount of PBd in solid ABS resins are developed. The ¹³C-NMR results and results from iodine monochloride titrations for PBd content are in good agreement. Resonances of PBd in ABS in the solid state are assigned on the basis of triad sequences of cis, trans, and vinyl-1,2 geometric isomers of butadiene. Computational methods are set forth for measuring directly from the ¹³C-NMR spectra the percent of cis, trans, and vinyl-1,2 isomers in PBd in the ABS resin. The NMR measurement of PBd microstructure appears to be preferable to infrared (IR) determinations. Relaxation parameters (T₁ and NOE) are reported for PBd in bulk ABS as a function of temperature and are analyzed in terms of a distribution of rotational correlation times. These relaxation parameters are similar to those of nongrafted PBd and indicate that the local motions in grafted and nongrafted PBd are similar.     

Characterization of propylene-ethylene block copolymers using solid state 13C-NMR spectroscopy

Commercial block copolymers of propylene with ethylene (PEBC) are multiphase systems comprising block and random copolymers as well as small amounts of homopolymers. At present, no satisfactory method exists for characterizing the “blocky” structure of these copolymers. This article aims to fulfill this need. Accordingly, the block and random copolymers of propylene with ethylene have been investigated using ¹³C CP/MAS NMR with high-power dipolar decoupling. Comparisons have been made between the spectra of block and random copolymers and it is shown possible to distinguish between them by means of an additional signal, appearing at 32.5δ, in block copolymers (attributable to block junctions). © 1992 John Wiley & Sons, Inc.     

Nylon 6 structure in solid state as studied by high-resolution 13C-NMR spectroscopy

High resolution ¹³C-NMR spectra of nylon 6 samples crystallized under various conditions and of a drawn sample were measured at room temperature by the cross polarization/magic angle spinning (CP/MAS) and pulse saturation transfer/magic angle spinning techniques. Additionally, ¹³C-NMR spectra of the drawn sample were measured at temperatures from 20 to 100°C by the CP/MAS technique and at 20 and 100°C by the low-power decoupling/magic angle spinning technique. The nylon 6 structure in the solid-state is discussed on the basis of these results. The solid-state ¹³C chemical shift data are used for reference in a study of conformation in solution.     

High-resolution solid-state 13C-NMR spectroscopy of cellulose nitrates

Solid-state ¹³C-NMR spectroscopy has been used to investigate the structure of cellulose nitrates prepared from cotton linters. The solid-state technique has the advantage that the entire range of substitution can be studied, which is not possible at present by solution methods. The spectra change progressively with increasing degree of substitution (DOS = 3 for cellulose trinitrate), and can be used to quantify the extent of substitution at C6, C2, and C3. Progressive nitration leads to elimination of the original C6 resonances of native cellulose by DOS = 1.39. The first nitration of C6 occurs in the amorphous regions, and this is complete by DOS = 0.50. Substitution at C6 is accompanied by decrystallization, as indicated by the decrease in the resonance assigned to crystalline C4, which also disappears at DOS = 1.39. A new resonance assigned to C1 appears at DOS = 0.28 at 101 ppm; the original C1 resonance for cellulose declines steadily and disappears by DOS = 2.65. This change is assigned to nitration of C2, based on the published solution spectra. Finally, development of intensity at 82 ppm at DOS = 1.83 is assigned to the effect of nitration at C3. There is no indication of any rearrangement of the unsubstituted regions analogous to those that occur on Mercerization of native cellulose.     

High resolution 13C-NMR spectroscopy of sodium carboxy methyl cellulose

Results of NMR studies on intact sodium carboxy methyl cellulose (SCMC) are presented. Similar studies in the literature are all on partially depolymerized SCMC. The degree of substitution and the relative distribution of substituents at OH-2, OH-3, and OH-6 of anhydro D -glucose residue in intact SCMC were determined by high resolution ¹³C-NMR spectroscopy (125 MHz). It is observed that the degree of substitution at OH-6 is almost equal to that at OH-3. In two SCMC samples, which are widely different in molecular weight and degree of substitution (ds), the relative reactivity order of the hydroxyl groups was found to be OH-2 > OH-6 ? OH-3. The NMR assignments were based on calculated shifts of carbons of anhydroglucose moiety in an oligosaccharide due to substitution.     

13C-NMR spectral studies on the distribution of substituents in water-soluble cellulose acetate

The degree of substitution (DS) and distribution of O-acetyl groups of water-soluble cellulose acetate (CA) were investigated by ¹³C-NMR. For this purpose, three different series of CA samples with low DS were prepared by respective homogeneous reaction, i.e., (1) deacetylation of cellulose triacetate (CTA) in acetic acid—water solution (D-series), (2) reaction of CTA with hydrazine (H-series), and (3) acetylation of cellulose with acetic anhydride in a 10% LiCl-dimethylacetamide solution (A-series). It was found that (i) water-soluble CA can be obtained only from D-series products, (ii) the DS value of water-soluble CA ranges from 0.5 to 1.1, (iii) the D-series products exhibit little difference between the relative DS values at C-2, C-3 and C-6 hydroxyl groups, and (iv) the relative DS at C-6 hydroxyl groups is very high compared to those at C-2 and C-3 hydroxyl groups in H- and A-series products. Aqueous solution of water-soluble CA (D-series sample) showed no gel—sol transition, even when the temperature was raised to 95°C. X-ray diffraction observations revealed that the water-soluble D-series samples were essentially noncrystalline, but the water-insoluble A-series samples were crystalline. It was also found that the relative ease of acetylation is C-6 > C-2 > C-3.     

Measuring the crystallinity index of cellulose by solid state 13C nuclear magnetic resonance

The crystallinity index of cellulose is an important parameter to establish because of the effect this property has on the utilization of cellulose as a material and as a feedstock for biofuels production. However, it has been found that the crystallinity index varies significantly depending on the choice of instrument and data analysis technique applied to the measurement. We introduce in this study a simple and straightforward method to evaluate the crystallinity index of cellulose. This novel method was developed using solid state ¹³C NMR and subtraction of the spectrum of a standard amorphous cellulose. The crystallinity indexes of twelve different celluloses were measured and the values from this method were compared with the values obtained by other existing methods, including methods based on X-ray diffraction. An interesting observation was that the hydration of the celluloses increased their crystallinity indexes by about 5%, suggesting that addition of water increased cellulose order for all the cellulose samples studied.     

Facile characterization of polymer-supported reagents using cross polarization magic angle spinning method in solid state 13C-NMR

Polymer-supported (PS) reagents can be easily characterized using a cross polarization magic angle spinning method in solid state (13)C-NMR. The technique was applied to the characterization of PS-dimethylimidazolidinone, analogue to potential heterogeneous dehydrating agent.     

13C-NMR study of cresyl benzoates

The proton-decoupled ¹³C FT—NMR spectra of para-, meta- and ortho-cresyl benzoates have been recorded and the observed signals have been assigned following the substituent additivity rule. The important features of diagnostic value of these spectra are discussed.     

1H and 13C-NMR data of hydroxyflavone derivatives

Many hydroxyflavone derivatives have been found in nature and shown to have many biological functions. Because their function is changed by the position and number of hydroxyl group, their structural identification is a fundamental and necessary step for understanding their functions. In the present study, the complete 1H and 13C NMR spectral assignments were presented for 6 hydroxyflavones, and NMR data of additional 14 hydroxyflavone derivatives were compared with those of the 6 hydroxyflavones. In addition, the partially incorrect NMR data of two of the dihydroxyflavones whose NMR data were previously reported were corrected.     

Identification of hardeners in solid epoxy resins by high-resolution 13C-NMR

CPMAS ¹³C-NMR spectra at 75 MHz with spinning side band suppression are presented for a series of epoxy resins cured with a variety of commercially important hardeners. The hardeners can be readily identified from the spectra; the high-field is important for distinguishing between related amine hardeners.     

A comparative CP/MAS 13C-NMR study of cellulose structure in spruce wood and kraft pulp

CP/MAS ¹³C-NMR spectroscopy in combination with spectral fitting was used to study the supermolecular structure of the cellulose fibril in spruce wood and spruce kraft pulp. During pulping, structures contributing to inaccessible surfaces in the wood cellulose are converted to the cellulose I allomorph, that is, the degree of order is increased. This increase is also accompanied by a conversion of cellulose I to cellulose I. Cellulose from wood composed of different cell types, that is, compression wood, juvenile wood, earlywood, latewood and normal wood exhibited a similar supermolecular structure. Assignments were made for signals from hemicellulose which contribute significantly to the spectral C-4 region (80–86 ppm) in kraft pulp spectra but substantially less to the corresponding region in wood spectra.     

Thermal study of four irradiated imidazoline derivatives in solid state

Four imidazoline derivatives: antazoline (AN), naphazoline (NN), tymazoline (TM), xylometazoline (XM), in the form of hydrochlorides in solid phase have been subjected to high energy e-beam irradiation from an accelerator (~10 MeV) at a dose varied from 25 to 200 kGy. The effects of the irradiation have been assessed by DSC, X-ray diffraction, FTIR, EPR and TLC. The standard sterilisation dose of 25 kGy has been found to produce changes in the properties of one derivative (XM), two other ones (AN and TM) have been found sensitive to doses >100 kGy, whereas NN has been resistant to irradiation in the whole range studied (25–200 kGy). EPR results indicated that the changes taking place in the therapeutic substances studied are related to radical formation. The irradiation induced changes in colour, a decrease or increase in the melting point, changes in the XRD pattern, small changes in the shape of FTIR peaks and the presence of radiolysis products. The XM compounds cannot be sterilised by irradiation because of the radiation induced changes in its physico-chemical properties.     

Molten state reactivity of difunctional cyanates: Thermal and spectroscopic studies by liquid and solid CP-MAS 13C-NMR

Using differential scanning calorimetry, we have investigated three difunctional cyanate monomers differing by their central group: bisphenol A dicyanate (BADCy), bisphenol E dicyanate (BEDCy), and hexafluorinated bisphenol A dicyanate (BAFDCy), to determine the effect of the central group on the molten state reactivity of heat-treated cyanates. To identify the different phenomena occurring during the heat cycle, which was followed by differential scanning calorimetry, ¹³C-NMR (liquid and solid) was undertaken. This technique was used to characterize the major products and side products formed. Using ¹³C-NMR and HPLC, we were able to detect the formation of compounds with a triazine ring at one chain end and a hydroxyl function at the other. The presence of the latter depended on the purity of the initial monomers. In light of the purity parameter, inherent in the synthesis of the products, we propose an order of reactivity, at molten state, of the polymerization of the three cyanate monomers in the temperature range of 180–300°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1245–1254 1997