Poly(vinylidene chloride-co-vinyl acetate): comprehensive microstructure analysis by NMR spectroscopy

The microstructure analysis of poly(vinylidene chloride-co-vinyl acetate) was done using chemical shift modeling and 2D NMR spectroscopy. Chemical shift modeling was applied to analyze the compositional sensitive resonances of quaternary carbon of vinylidene chloride unit. Reactivity ratios determination was done from the diad and triad fractions. To resolve the complex ¹H and ¹³C{¹H} NMR spectra of copolymers, 2D ¹H/¹³C hetero-nuclear single quantum coherence (HSQC), ¹H/¹H total correlation spectroscopy (TOCSY) and hetero-nuclear multiple bond correlation (HMBC) experiments were conducted. The combination of 2D NMR experiments supported by chemical shift modeling enabled to assign the complex and overlapping proton and carbon-13 resonances unambiguously.     

Investigation of microstructure of the acrylonitrile‐styrene‐glycidyl methacrylate terpolymers by 1D and 2D NMR spectroscopy

Acrylonitrile‐styrene‐glycidyl methacrylate (N/S/G) terpolymers were prepared by bulk polymerization by using benzoyl peroxide as initiator and analyzed by NMR spectroscopy. The compositions of terpolymers were determined by quantitative ¹³C{¹H}‐NMR spectra and compared with those calculated by Goldfinger's equation by using comonomer reactivity ratios: r_NS = 0.04, r_SN = 0.40; r_NG = 0.22, r_GN = 1.37; r_SG = 0.44, r_GS = 0.53. The ¹³C{¹H}‐ and ¹H‐NMR spectra were overlapping and complex. The spectral assignments were done with the help of distortionless enhancement by polarization transfer and two‐dimensional ¹³C‐¹H heteronuclear single quantum correlation experiments. 2D total correlated spectroscopy was used to ascertain the various coupling between the protons. The methyl, methine, methylene, and oxymethylene carbon resonances showed compositional sensitivity. 2D nuclear Overhauser enhancement spectroscopy (NOESY) experiment was used to ascertain the spatial proton–proton couplings. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1779–1790, 2003     

One‐ and two‐dimensional nuclear magnetic resonance studies on the compositional sequence and the microstructure of acrylamide/acrylonitrile copolymers

Copolymers containing acrylamide (A) and acrylonitrile (B) units of different compositions were synthesized by free‐radical solution polymerization. The reactivity ratios were estimated by the Kelen Tudos and nonlinear error‐in‐variable methods. The triad sequence distribution in terms of A‐ and B‐centered triads were obtained from ¹³C{¹H}‐NMR spectroscopy. The complete spectral assignments in terms of compositional and configurational sequences of the overlapping carbon and proton spectra of these copolymers were done using distortionless enhancement by polarization transfer (DEPT), two‐dimensional proton‐detected heteronuclear correlation (inverse‐HETCOR), and total correlated spectroscopy (TOCSY) experiments. The Monte Carlo simulation was used to study the effect of the fractional conversion on the triad fractions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 55–67, 1999     

Microstructure analysis of poly(styrene‐co‐vinylidene chloride) copolymers by NMR spectroscopy

Poly(styrene‐co‐vinylidene chloride) (S/V) copolymers were prepared by free‐radical photopolymerization using uranyl nitrate as an initiator. The microstructure of the copolymer S/V was investigated by ¹H‐ and ¹³C{¹H}‐NMR, ¹H–¹³C‐heteronuclear shift quantum correlation (HSQC) NMR, and homonuclear total correlated spectroscopy (TOCSY). The ¹H‐NMR spectra of the copolymers is complex due to overlapping resonance signals of the various triad configurations. Assignments were made up to the triad and tetrad levels for the methylene and methine regions using two‐dimensional HSQC experiments. A ¹³C‐distortionless enhancement by polarization transfer (DEPT) spectrum was used to differentiate between the carbon resonance signals of methine and the methylene units. The geminal couplings in the methylene protons and vicinal coupling between the methine and methylene protons were detected from the TOCSY spectra. Monte Carlo simulations were used to investigate the effect of the degree of polymerization on the triad fractions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 544–554, 2001     

Application of high-resolution, two-dimensional 1H and 13C nuclear magnetic resonance techniques to the characterization of lipid oxidation products in autoxidized linoleoyl/linolenoylglycerols

Subjection of polyunsaturated fatty acid (PUFA)-rich culinary oils to standard frying episodes generates a range of lipid oxidation products (LOP), including saturated and α,β-unsaturated aldehydes which arise from the thermally induced fragmentation of conjugated hydroperoxydiene precursors. Since such LOP are damaging to human health, we have employed high-resolution, two-dimensional ¹H-¹H relayed coherence transfer, ¹H-¹H total correlation, ¹H-¹³C heteronuclear multiple quantum correlation, and ¹H-¹H J-resolved nuclear magnetic resonance (NMR) spectroscopic techniques to further elucidate the molecular structures of these components present in (i) a model linoleoylglycerol compound (1,3-dilinolein) allowed to autoxidize at ambient temperature and (ii) PUFA-rich culinary oils subjected to repeated frying episodes. The above techniques readily facilitate the resolution of selected vinylic and aldehydic resonances of LOP which appear as complex overlapping patterns in conventional one-dimensional spectra, particularly when employed in combination with solvent-induced spectral shift modifications. Hence, much useful multi-component information regarding the identity and/or classification of glycerol-bound conjugated hydroperoxydiene and hydroxydiene adducts, and saturated and α,β-unsaturated aldehydes, present in autoxidized PUFA matrices is provided by these NMR methods. Such molecular information is of much value to researchers investigating the deleterious health effects of LOP available in the diet.     

Two-dimensional n.m.r. analysis of aromatic fractions from a coal liquefaction solvent

Two-dimensional n.m.r. experiments correlating heteronuclear ¹H-¹³C and homonuclear ¹H-¹H spin-spin coupling have enabled various aliphatic groups to be identified unambiguously in complex mono- and diaromatic fractions from a coal liquefaction solvent. These groups include those that are generally difficult to identify by g.c.-m.s. such as five membered rings and CH₃ substituted in cyclic structures.     

Single-Step analysis of individual conjugated bile acids in human bile using 1H NMR spectroscopy

¹H and ¹³C NMR spectra of intact human bile were assigned using one-dimensional (¹H and ¹³C) and two-dimensional (¹H-¹H and ¹H-¹³C) experiments. Individual conjugated bile acids—glycocholic acid, glycodeoxycholic acid, glycochenodeoxycholic acid, taurocholic acid, taurodeoxycholic acid, and taurochenodeoxycholic acid—were identified. The bile acids were quantified accurately and individually in a single step by using distinct and characteristic amide signals. Making use of ¹³C NMR, the study also suggests a way to analyze unconjugated bile acids separately, if present. Chemical shift assignments and rapid single-step analysis of individual conjugated bile acids from intact bile presented herein may have immense utility in the study of bile acid metabolism and deeper understanding of hepatobiliary diseases.     

Microstructure determination of isobornyl methacrylate-styrene copolymer by NMR spectroscopy

An investigation of the microstructure of isobornyl methacrylate - styrene (I/S) copolymers prepared by the atom transfer radical polymerization (ATRP) using methyl-2-bromopropionate as an initiator and PMDETA copper complex as catalyst under nitrogen atmosphere at 70 °C has been done by two-dimensional NMR techniques. 2D- HSQC and TOCSY have been utilized to resolve the complex ¹H NMR spectrum and to establish the compositional and configurational sequences of isobornyl methacrylate-styrene (I/S) copolymers. 2D HSQC and TOCSY spectra showed compositional and configurational sensitivity of α-methyl carbon of I unit and methine proton of S unit and are assigned up to the triad level. The methylene carbon (C₁₀) also shows triad level of compositional sensitivity in 2D HSQC spectra. Heteronuclear multiple-bond correlation (HMBC) spectroscopy has been used to study carbonyl/quaternary carbon-proton coupling. The carbonyl and quaternary carbons showed compositional and configurational sensitivity upto the triad level. The values of reactivity ratios were determined by Kelen-Tudos (KT) and nonlinear error in variable method (RREVM) using copolymer composition data that were determined by ¹H NMR spectrum. Reactivity ratios of co-monomers in I/S copolymer, determined from a linear Kelen-Tudos method (KT) and non-linear Error-in-Variable Method (EVM), are r_I?=?0.39?±?0.09, r_S?=?0.44?±?0.08 and r_I?=?0.42, r_S?=?0.47, respectively.     

Segmental mobility in poly(isoprene) rubber studied by deuterium-carbon NMR correlation spectroscopy

Summary A HMQC based deuterium-carbon correlation method is used for the first time to study the segmental mobility in a fully deuterated poly(isoprene) (PI) rubber network. The isotropic J _CD couplings can be utilized for polarization transfer between ²H and ¹³C spins in a mobile solid polymer. This makes it possible to correlate the ²H resonances with the ¹³C chemical shifts of the attached carbon in a two-dimensional (2D) experiment, and thus allow the extraction of the individual ²H signals. The experimental data obtained from the 2D correlation spectrum indicates differences in the segmental mobility of the C-D vectors in perdeuterated PI. The conclusions are fully consistent with ²H and ¹³C T ₁ relaxation data. The results shown in this paper demonstrate the potential of ²H-¹³C NMR correlation spectroscopy in solid systems which produce overlapped 1D ²H spectra. Received: 11 December 2000/Revised version: 1 March 2001/Accepted: 1 March 2001     

Proof of ether-bridged condensation products in UF resins by 2D NMR spectroscopy

The existence of ether-bridged condensation products in urea-formaldehyde (UF) resins is still disputed in the literature as these products have never been isolated or fully characterized. Using ¹H-¹⁵N gradient heteronuclear single quantum correlation (gHSQC) experiment, ¹H-¹³C gHSQC experiment and ¹H-¹³C gradient heteronuclear multiple bond correlation (gHMBC) experiment a, methylolurea hemiformal compound (urea compound with oligomeric chains $-\rm{CH}_{2}\;{\rm O[CH}_{2}{\rm O]}{\mathrm {n}}{\rm H}$ and $n\geq 1$ ) and a symmetrical compound, most likely an ether-bridged condensation product, in a UF resin sample were characterized. The results were confirmed by 2D NMR ¹³C-¹³C gradient correlated spectroscopy (gCOSY) experiment using ¹³C labeled ureaformaldehyde samples. Spectroscopic chemical shifts of the proposed ether-bridged condensation product in ¹⁵N, ¹³C, ¹H NMR spectroscopy were assigned. Furthermore, individual peak assignments are provided for the methylolurea hemiformal moiety.     

Microstructure analysis of methyl acrylate/methyl methacrylate copolymers by two‐dimensional NMR spectroscopy

Methyl acrylate (A)/methyl methacrylate (B) copolymers of different compositions were synthesized in bulk at 50°C and the compositions were determined from ¹H NMR spectra. Reactivity ratios were optimized using the least square methodology. Compositional and configurational assignments were done using two‐dimensional (2D) Heteronuclear Single Quantum Correlation (HSQC) and Total Correlation Spectroscopy (TOCSY) experiments. Methylene proton and carbon resonances were assigned for compositional and configurational sensitivity at tetrad level. Carbon resonances of methine group of methyl acrylate were assigned for compositional sensitivity up to triad level with the help of 2D HSQC spectra. α‐Methyl group of methyl methacrylate was assigned up to triad level of compositional and configurational placements for carbon and proton resonances by 2D HSQC spectroscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1437–1445, 2006     

New copper(II) complexes of polyampholyte and polyelectrolyte polymers: Solid-state NMR, FTIR, XRPD and thermal analyses

Novel solid copper(II) complexes were obtained from the polyampholyte poly(EGDE-MAA-IM) and the polyelectrolyte poly(EGDE-MAA) polymers with copper salts at different concentration levels.The materials were characterized employing solid-state Nuclear Magnetic Resonance (NMR), Fourier Transform infrared (FTIR), X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and thermogravimetry (TG).The reticulation induced by MAA in these materials against the poly(EGDE-IM) gel was analyzed by DSC. The coordination behavior of the carboxylic acid of MAA, compared to that provided by the imidazole ring, was studied through solid-state ¹³C NMR and changes in the FTIR spectra. The non-homogenous character of the doped and undoped materials was analyzed by the glass transition temperature (T_g), 2D ¹H-¹³C WISE NMR and proton spin-lattice relaxation time in the rotating frame (T^H_1ρ). In particular, the T^H_1ρ and T^H₁ values in the complexes decreased with the Cu(II) concentration, showing the high sensitivity of both parameters to the presence of a paramagnetic ion. Finally, the thermogravimetric studies indicated that the presence of the imidazole ring was decisive for the stability of the Cu(II) complexes and for the undoped polymers.     

Synthesis and characterization of novel polyampholyte and polyelectrolyte polymers containing imidazole,triazole or pyrazole

Novel soluble and non-soluble polymers based on methacrylic acid, ethylene glycol diglycidyl ether and pyrazole, triazole or imidazole were obtained by a one-spot synthetic strategy. The new materials were characterized by spectroscopic techniques (FT-IR, and solution- and solid-state NMR). Evidence on the covalent binding of the different heterocycles to the non-soluble matrix was given by the unequivocal assignment of the ¹³C solid-state NMR spectra. Proton relaxation times in the rotating frame and two-dimensional wideline separation (¹H-¹³C WISE) NMR spectra were used to assess their molecular dynamics. The higher synthetic yield of polyampholytes bearing triazole or pyrazole correlated with a lower molecular motion and a higher cross-linking degree. The polyelectrolyte effect of these materials was exhaustively explored through the acid-base properties, swelling and zeta potential. The quaternization of heterocyclic residues, responsible for adsorptive properties, was studied taking into account that these materials are attractive for analytical, environmental and biotechnological processes.     

Structural analysis of cellulose triacetate polymorphs by two-dimensional solid-state C-C and H-C correlation NMR spectroscopies

For the elucidation of the crystal structures of the two crystalline allomorphs of cellulose triacetate (CTA), namely CTA I and CTA II, two-dimensional (2D) solid-state through-bond ¹³C-¹³C and ¹H-¹³C correlations NMR techniques applied to the two crystalline allomorphs of CTA. As a result, the ¹³C and ¹H chemical shifts of the glucopyranose ring of CTA I and CTA II were completely assigned by the 2D NMR spectra of these allomorphs. On the 2D ¹³C-¹³C correlation spectrum of CTA II, two sets of the ¹³C-¹³C correlations from C1 to C6 were observed. This indicated that the CP/MAS ¹³C NMR spectrum of CTA II can be characterized by its overlapping of the ¹³C subspectra of two kinds of 2,3,6-triacetyl-anhydroglucopyranose units and that there are two magnetically non-equivalent sites in the unit cell of CTA II. In the case of CTA I, the numbers of respective ¹³C and ¹H shifts of CTA I agreed with the those of the glucopyranose residue in the allomorph, strongly suggesting that the asymmetric unit of CTA I is only one glucose residue. In addition, conformational differences in the exocyclic C5-C6 bonds between CTA I and CTA II were strongly suggested by the notable differences in the ¹H and ¹³C chemical shifts at the C6 sites of these allomorphs.     

Characterization of unsaturated polyester and alkyd resins using one‐ and two‐dimensional NMR spectroscopy

One‐ (1D) and two‐dimensional (2D) ¹H‐ and ¹³C‐NMR spectroscopy was used to characterize polyester and alkyd resins used in the coatings industry. The wealth of chemical composition information of the ¹H‐ and ¹³C‐NMR 1D spectra of the resins is revealed through 2D NMR experiments that spread chemical shifts in two dimensions, thus facilitating the peak assignment of the various components of the resins. It is shown that the types of polyols, acids, and vegetable oils used to modify the resins can be efficiently traced by NMR spectroscopic techniques. Information on the quantitative composition of the resins and especially the abundance of unsaturated fatty acid double bonds, which influences resin dryability and hardness, can be easily extracted from the ¹H‐NMR spectra upon successful assignment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1881–1888, 2003     

Formation of the crystalline inclusion complex between γ-cyclodextrin and poly(N-acetylethylenimine)

Poly(N-acetylethylenimine) was found to form a crystalline inclusion complex with γ-cyclodextrin (CD). It did not form crystalline inclusion complexes with α-CD or β-CD. It is a hydrophilic, nitrogen atom-containing polymer that forms a crystalline inclusion complex with CD. FT-IR spectroscopy, thermogravimetry analysis, X-ray diffraction, ¹H NMR spectra and ¹³C CP/MAS NMR spectra were used to characterize the structure and property of the crystalline inclusion complex.     

One- and two-dimensional nuclear magnetic resonance studies on the compositional sequence and the microstructure of acrylonitrile–pentyl methacrylate copolymers

The chemical microstructure of acrylonitrile–pentyl methacrylate (A–P) copolymers prepared by photopolymerization using uranyl ion as the photo sensitizer is analyzed by ¹³C{¹H} nuclear magnetic resonance spectroscopy. The composition of the copolymers were determined by elemental analysis, and comonomer reactivity ratios were determined by the Kelen–Tudos (KT) and the error in variable (EVM) methods. The terminal model reactivity ratios obtained from the EVM method are r_A = 0.20 and r_P = 2.62. The complete spectral assignment of the overlapping proton and carbon spectra of these copolymers were done with the help of distortionless enhancement by polarization transfer and two-dimensional ¹H–¹³C heteronuclear shift correlation (inverse HETCOR) spectroscopy. The assignment of the various conformational and configurational sequences in the proton spectrum were made possible by two-dimensional correlated spectroscopy and total correlation spectroscopy experiments. Monte Carlo simulation was used to study the effect of the degree of polymerization on the triad fractions. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 69: 2507–2516, 1998     

High resolution 13C n.m.r. spectra of solid isotactic polypropylene

The high-resolution ¹³C n.m.r. spectra of three samples of solid isotactic polypropylene are reported. The spectra, obtained under conditions of proton dipolar-decoupling and fast magic-angle rotation and using cross-polarization, are of annealed and quenched samples of the α-crystalline form and of a sample of the β-crystalline form. Attention is drawn to the importance of knowing the proton relaxation characteristics in these experiments and some illustrative proton T_1? data are given. The ¹³C n.m.r. spectrum of the annealed sample of the α-crystalline form shows well-resolved splittings of the methyl and methylene resonances in a 2:1 intensity ratio. These splittings are interpreted in terms of the crystal structure of the α-form as suggested by X-ray diffraction. Quenching the α-form causes significant changes in the spectrum including a loss of resolution of the splittings obtained from the annealed sample. The β-form shows broad symmetrical resonances for the methyl and methylene carbons. The chemical shifts and other spectral features are discussed in the light of the proposed crystal structures and the effects likely to be produced by quenching.     

Comprehensive analysis of stereoregularity and sequence distribution in 2-N-carbazolylethyl acrylate and methyl methacrylate copolymers by 2D NMR spectroscopy and their thermal studies

A series of 2-N-carbazolylethyl acrylate (C) and methyl methacrylate (M) copolymers with varying compositions were prepared in toluene at 60 °C using AIBN as an initiator. The molar outfeed ratio (F_C) for various compositions was determined from ¹H NMR spectra. Reactivity ratios calculated using Kelen-Tudos (KT) and non-linear error in variable (RREVM) methods were found to be r_C=0.43±0.8 and r_M=2.78±0.52. Molecular weight distribution was determined by gel permeation chromatography (GPC). The methine carbon of C unit showed splitting up to the pentad level in ¹³C{¹H} NMR spectra and was found to be sensitive to the variation in C/M copolymer compositions. The backbone methylene and carbonyl carbons of both M and C unit along with α-methyl carbon of the M unit showed both compositional and configurational sensitivity. Distortionless enhancement by polarization transfer (DEPT) helped in differentiating the methylene carbon signals from the methine and methyl carbon resonances. 2D heteronuclear single quantum coherence (HSQC) and 2D total correlation spectroscopy (TOCSY) were used in tandem to deduce all spectral assignments. 2D heteronuclear multiple bond coherence (HMBC) played an important role in studying the stereoregularity of the carbonyl carbon. The trend in variation of glass transition temperature (T_g) of various C/M copolymer compositions was also studied.     

Study on β-cyclodextrin grafting with chitosan and slow release of its inclusion complex with radioactive iodine

β-CD-2-CTS was synthesized by β-cyclodextrin reacting with p-toluenesulfonyl chloride, then grafting with chitosan. The infrared spectra analysis and ¹³C NMR confirmed that β-cyclodextrin reacted with p-toluenesulfonyl chloride at the 2-position carbon atom in the substituted glucose unit of β-cyclodextrin and formed β-CD-2-OTs. In the ¹³C NMR of β-CD-2-OTs, the characteristic peak of the 2-postion carbon atom in the substituted glucose unit of β-cyclodextrin appeared at 78.43 ppm. β-CD-2-CTS was characterized with infrared spectra analysis and X-ray diffraction. In the infrared spectra of β-CD-2-CTS, the characteristic peak of α-pyanyl vibration of β-CD was at 848.6 cm⁻¹. The characteristic peak of β-pyanyl vibration of CTS was at 894.9 cm⁻¹. The X-ray diffraction analysis showed that the peak at 2θ = 20° decreased greatly in β-CD-2-CTS. The polymer inclusion complex of β-CD-2-CTS with iodine was prepared and its inclusion ability was studied. The experimental results showed that a nice bit of iodine was included with β-CD-2-CTS and formed a stable inclusion complex. After the subcutaneous implantation of the polymer inclusion complex of β-CD-2-CTS with ¹³¹I₂ in rats, ¹³¹I₂ exhibited the property of slow release. ¹³¹I₂ in the blood of rats decreased slowly. ¹³¹I₂ in the blood of rats maintained approximately half of maximum for 70 days later, and maintained much higher radioactivity in the organs of rats compared to the inclusion complex of β-CD with ¹³¹ I₂, too. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2414–2421, 2001