Assignment of finely resolved 13C NMR spectra of poly(vinyl acetate)

¹³C NMR spectra of two poly(vinyl acetate)s (PVAC) with different tacticities (r‐diad, 0.54 and 0.57) were measured, and their peak intensities were compared with the calculated ones. The methine carbon signals were assigned with pentads in the order of mmmm, mmmr + rmmr, rmrr + mmrr, rrrr, mmrm, rmrm, mrrr, mrrm from low field. The methylene carbon signals were assigned with tetrads (partly with hexads) as rmr, rrr(mrrrm, mrrrr, rrrrr), mmr + mrr, mrm and mmm from low field. Some assignments are different from those previously reported. The methyl carbon signals showed splittings which were partly assigned.     

The effects of overall composition and monomer sequence distribution on the infrared carbonyl stretching frequencies of ethylene–vinylacetate and styrene–vinylacetate copolymers

The vinyl acetate centered triad fractions of some free radically prepared ethylene–vinyl acetate and styrene–vinyl acetate copolymers have been determined from the patterns of vinyl acetate methine carbon peaks in their ¹³C nuclear magnetic resonance (NMR) spectra. The positions and shapes of the carbonyl bands in the infrared (IR) absorption spectra of the copolymers recorded in chloroform are shown to depend on the compositions of the copolymers and on the proportions of the various vinyl acetate centered triads. Infrared absorption measurements may thus be used in part to characterize the monomer sequence distributions of these copolymers.     

Nuclear magnetic resonance studies on microstructure of ethylene copolymers. VI. Carbon-13 spectra of ethylene–vinyl acetate copolymers

The 22.6-MHz Fourier-transform noise-decoupled ¹³C (carbon-13) NMR spectra of several ethylene–vinyl acetate (E–VA) copolymers were obtained. We found that triad information on monomer placement can be deduced from carbonyl resonances, triad and pentad information can be deduced from methine carbon resonances, and triad information is available from the methylene carbon resonances. The random comonomer distributions in E–VA polymerizations were demonstrated up to pentad placements. In addition, the use of model-compound data in the analysis of copolymer spectra was shown.     

Grafting reactions of vinyl acetate onto poly[(vinyl alcohol)-co-(vinyl acetate)]

The grafting preference of vinyl acetate onto the methine carbon of poly(vinyl alcohol) (PVOH) versus the acetate group of poly(vinyl acetate) (PVAc) was determined as part of an attempt to prepare novel branched PVOH from partially hydrolyzed PVAc. The results showed long chain grafting on the acetate groups of the PVAc units rather than the methine carbons of the PVOH or PVAc units. Decreasing the monomer or initiator concentration decreased the molecular weight of the graft copolymer formed. Of the initiators studied, ammonium persulfate gave the largest increase in copolymer molecular weight. Both hydrolysis and reacetylation combined with gel permeation chromatography (GPC) and ¹³C-NMR of the fully hydrolyzed material were used to estimate the number and location of grafts. © 1996 John Wiley & Sons, Inc.     

One- and two-dimensional NMR studies of methyl acrylate/vinyl acetate/N-vinyl carbazole terpolymers

Terpolymers of methyl acrylate/vinyl acetate/N-vinyl carbazole (M/A/C) with different compositions were synthesized by solution polymerization using AIBN as an initiator. Composition of terpolymers was determined from quantitative ¹³C{¹H} NMR spectrum. Two-dimensional heteronuclear single quantum correlation (HSQC) and total correlated spectroscopy (TOCSY) were used to assign the methylene and methine carbon resonances by analyzing two and three bond order couplings. Various resonance signals were assigned to different compositional and configurational sequences with the help of one- and two-dimensional NMR spectra. Three and four bond order coupling between carbonyl carbon and other neighboring protons have been investigated with the help of 2D heteronuclear multiple bond correlation (HMBC) spectra. The complex and overlapped ¹H NMR spectrum of terpolymer was analyzed completely with the help of 2D HSQC and TOCSY spectra.     

Effect of solvent for vinyl acetate polymerization on microstructure of poly(vinyl alcohol)

The solution polymerization of vinyl acetate was carried out in several solvents at 0 to 100°C, using 2,2′-azobisisobutyronitrile as initiator. For the resulting poly(vinyl alcohol) (PVA), iodinecoloration, 1,2-glycol structure and tacticity were observed. The pentad tacticity of PVA was estimated from its methine carbon spectra by means of ¹³C-FTNMR spectrometer. Iodine-coloration ability of PVA varied markedly with the type of polymerization solvent and decreased in the following order: phenol > aq. phenol > methyl alcohol > ethyl acetate > DMSO, ethylene carbonate. The syndiotactic fraction in PVA also decreased with polymerization solvent in the same order as that of iodine coloration, while 1,2-glycol content of PVA was not almost affected by polymerization solvent except for phenol and aq. phenol. In solution polymerization performed, effect of polymerization temperature on tacticity was less than that of solvent.     

Sequence analysis of ethylene sulphide-propylene sulphide copolymers by carbon-13 nuclear magnetic resonance

Ethylene sulphide-propylene sulphide copolymers, prepared with anionic type catalysts, have been investigated by ¹³C NMR. The peaks have been assigned both in terms of diad and triad monomer sequences and in terms of tacticity. It has been shown that the propylene sulphide monomer units were directionally oriented and the tacticity was approximately random. We have also determined the effect of methyl substitution in various positions on the chemical shift of the main chain carbon atoms.     

Characterization of copolymers of vinyl acetate with ethyl α-cyanocinnamate

Alternating and random copolymers of ethyl α-cyanocinnamate and vinyl acetate were studied. Infrared, ¹H, and ¹³C spectra of the copolymers are discussed by comparison with a model compounds, poly(vinyl acetate), and various copolymers. The decomposition temperature and T_g of copolymers of various composition, studied by TMA and DSC, increase both with increasing content of ethyl α-cyanocinnamate.     

13C-NMR study of chlorinated ethylene–vinyl acetate copolymers

¹³C-NMR has been used to analyze the microstructures of a series of experimental chlorinated ethylene–vinyl acetate copolymers (15–56% CI). Previously established line assignments for EVA copolymers and substituent effect parameters for chlorine have enabled us to tentatively assign partial structures up to five carbon atoms in length. The ¹³C-NMR analyses of a commercial vinyl chloride–vinyl acetate copolymer, a commercial vinyl chloride–vinyl acetate–ethylene terpolymer, and a commercial chlorinated polyethylene support the structural assignments. Data obtained for the experimental resins indicate that the acetate groups influence the way in which chlorine is added to the polymer chain. furthermore, the data indicate the acetate groups undergo little, if any, chlorination.     

Carbon-13 NMR relaxation and transitions in polymers

High-resolution proton-decoupled carbon-13 nuclear magnetic resonance relaxation parameters have been obtained as a function of temperature for a set of completely amorphous polymers, semicrystalline polymers, and a series of ethylene–vinyl acetate copolymers. With these samples the nature of the glass temperature, other postulated amorphous transitions, and the β transition were investigated. For the completely amorphous polymers, the average correlation times depend on temperature according to the Williams–Landel–Ferry relation. Spectral collapse occurs at temperatures whose ratio to T_g is in the range 1.2–1.4 and corresponds to a correlation time of about 10^?7s. The loss of resolvable spectra is demonstrated to be a consequence of experimental methods and is not due to the occurrence of another amorphous transition. Both the methylene and methine carbons can be resolved for the ethylenevinyl acetate copolymers. Although the correlation time for the methylene carbon is continuous and resolvable through the β transition region, the methine branch-point resonance is lost. The implication of these results to the molecular nature of the β transition is discussed.     

13C nuclear magnetic resonance studies on the stereochemical configurations of 2,4-dimethoxypentane and poly(alkyl vinyl ethers)

¹³C nuclear magnetic resonance (CMR) spectra were obtained for 2,4-dimethoxypentane, which is a model compound of poly(methyl vinyl ether), and the effects of the solvent and temperature on the chemical shifts were investigated. CMR spectra of poly-(alkyl vinyl ethers) were also determined and analyzed. The diad tacticities were obtained from β-methylene carbon resonances of poly(methyl vinyl ether), poly(ethyl vinyl ether), and poly(isobutyl vinyl ether), but not from those of poly(isopropyl vinyl ether) and poly(tert-butyl vinyl ether). The methoxyl carbon resonance of poly(methyl vinyl ether) and the ethoxyl methylene carbon resonance of poly(ethyl vinyl ether) showed splittings corresponding to pentad and triad sequences, respectively. The α-methine and quaternary carbon resonances of poly(tert-butyl vinyl ether) showed splittings corresponding to pentad and triad sequences, respectively.     

Donor-Acceptor Complexes in Copolymerization. IV. Alternating Tendency in Free Radical Copolymerization. NMR Analyses of Alternating and Random Copolymers

An NMR investigation was carried out on variable composition, random and equimolar, alternating copolymers of acrylonitrile (A) with styrene (S), isoprene (I), and butadiene (B). The NMR spectra of the SA copolymers contained peaks at 3 τ (aromatic ring protons), 7.2-7.5 τ (CH protons of A), and 8.1 -8.5 τ (CH and CH₂ protons of S and CH₂ protons of A). All NM R peaks of the alternating SA copolymer were shifted to the higher field due to the shielding effect of S. The NMR spectra of the IA copolymers contained peaks at 4.72-4.91 τ (?CH protons of I), 7.27-7.4 τ (CH protons of A), 7.71-7.93 τ (CH₂ protons of I), and 8.35 τ (CH₃ protons of I and CH₂ protons of A). The peaks at 4.72 τ (?CH) and 7.72 τ (CH₂) were assigned to I in the I-A diad and the peaks at 4.91 τ (?CH) and 7.93 τ (CH₂) were assigned to I in the I-I diad. The NMR spectra of the BA copolymers contained peaks at 4.4-4.6 τ (?CH protons of B), 7.2-7.5 τ (CH protons of A), 7.71-7.97 T (CH₂ protons of B), and 8.0-8.4 τ (CH₂ protons of A). The peaks at 4.42 τ (?CH) and 7.71 τ (CH₂) were assigned to B in the B-A diad and the peaks at 4.6 τ (?CH) and 7.9 τ(CH₂) were assigned to B in the B-B diad. The alternating structure of the copolymers prepared through metal halide-activated complexes was confirmed by NMR analysis. The random copolymers prepared by free radical initiation contain a high concentration of alternating sequences, as anticipated from the values of r₁ and r₂ where r₁(S, I, and B) is 6-10 times higher than r₂ (A).     

Microstructure of glycidylmethacrylate/vinyl acetate copolymers by two‐dimensional nuclear magnetic resonance spectroscopy

Glycidylmethacrylate/vinyl acetate copolymers were prepared by solution polymerization with benzene as a solvent and benzoyl peroxide as an initiator. Copolymer compositions were determined from ¹H NMR spectra, and comonomer reactivity ratios were determined by the Kelen–Tudos (KT) method and the nonlinear least‐squares error‐in‐variable method (EVM). The reactivity ratios obtained from KT and EVM were r_G = 37.4 ± 12.0 and r_V = 0.036 ± 0.019 and r_G = 35.2 and r_V = 0.03, respectively. Complete spectral assignments of ¹³C and ¹H NMR spectra were done with the help of distortionless enhancement by polarization transfer and two‐dimensional ¹³C–¹H heteronuclear single quantum coherence and total correlation spectroscopy. The methyl, methine, and methylene carbon resonance showed both stereochemical and compositional sensitivity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4051–4060, 2001     

13C-{1H} NMR spectra of episulphide copolymers

Ethylene sulphide-isobutylene sulphide and propylene sulphide-isobutylene sulphide copolymers have been prepared using anionic catalysts and investigated by ¹³C-{¹H} NMR spectroscopy. The carbon-13 NMR spectra are assigned in terms of diad and triad sequences. There is discussion of the effects of mono- or dimethyl substitution in the α, β, γ or δ positions on the chemical shift of the main chain carbon atoms. It has also been shown that for isobutylene sulphide, as for propylene sulphide, under the influence of an anionic catalyst, there is a normal ring opening only at the primary carbon atom.     

The effect of copolymerization on transition temperatures of polymeric materials

The relationship between transition temperatures and copolymer composition was studied by DSC. Three types of copolymers were studied: styrene-acrylonitrile (SAN), vinyl chloride-vinyl acetate (VC-VA), and ethylene vinyl acetate (EVA). SAN's and VC-VA's are amorphous copolymers, whereas EVA's are semi-crystalline copolymers. The variation of the glass transitions and the crystalline melting are discussed in this study.     

Reactivity ratios and microstructure determination of vinyl acetate–alkyl acrylate copolymers by NMR spectroscopy

(Vinyl acetate)/(ethyl acrylate) (V/E) and (vinyl acetate)/(butyl acrylate) (V/B) copolymers were prepared by free radical solution polymerization. ¹H-NMR spectra of copolymers were used for calculation of copolymer composition. The copolymer composition data were used for determining reactivity ratios for the copolymerization of vinyl acetate with ethyl acrylate and butyl acrylate by Kelen-Tudos (KT) and nonlinear Error in Variables methods (EVM). The reactivity ratios obtained are r_v = 0.03 ± 0.03, r_E = 4.68 ± 1.70 (KT method); r_v = 0.03 ± 0.01, r_E = 4.60 ± 0.65 (EV method) for (V/E) copolymers and r_v ? 0.03 ± 0.01, r_B ? 6.67 ± 2.17 (KT method); r_v = 0.03 ± 0.01, r_B = 7.43 ± 0.71 (EV method) for (V/B) copolymers. Microstructure was obtained in terms of the distribution of V- and E-centered triads and V- and B-centered triads for (V/E) and (V/B) copolymers respectively. Homonuclear ¹H 2D-COSY NMR spectra were also recorded to ascertain the existence of coupling between protons in (V/E) as well as (V/B) copolymers. © 1995 John Wiley & Sons, Inc.     

Reactivity differences between isolated and vicinal vinyl acetate functions in high pressure ethylene/vinyl acetate copolymers

Three ethylene/vinyl acetate copolymers (3.5, 12.0 and 18.8 mol% VA; average melt index 8.5 g/10 min) were transformed into ethylene/vinyl alcohol copolymers and ethylene/vinyl alcohol/vinyl acetate terpolymers by homogeneous saponification. The reaction rate increased with mol% VA. This feature originated in the reactivity differences beteen vicinal and isolated VA functions. Simultaneous steric and polarity effects caused the reaction rate differences. ¹H-NMR, i.r., dielectric measurements and additional saponification reactions confirmed the difference of reactivity.     

NMR Determination of the Microstructure of Polyvinyl Chloride Sulfone). II. 13C-(1H) Spectra

The ¹³C-(¹H) NMR spectra of poly(vinyl chloride sulfone)s with macroscopic compositions corresponding to the ratio vinyl chloride (V):SO₂(S) = n from ca. 1 to 4 have been analyzed in terms of comonomer sequences and configurational placements. In the copolymer with n ? 1, methylene and methine carbons in SVS sequences were resolved and were sensitive to “across SO₂” tacticity. No SVS sequences were observed in the copolymer with n = 2.0, confirming that it had a regular SVVS structure, which also showed a high “internal” stereosequence regularity. It was not possible to discriminate the methylene or methine carbon atoms in S(V)_n S sequences with n ≥ 2.     

On the assignment of the carbon-13 NMR spectrum of bilirubin

An individual assignment of certain peaks in the proton and ¹³C NMR spectra of bilirubin and of bilirubin dimethyl ester is described. The assignment was achieved through the spectra of vinylneoxanthobilirubinic acid and by off-resonance decoupled ¹³C spectra of bilirubin dimethyl ester. The signals due to the endo and exo vinyl groups were separately assigned. This assignment allows a rational interpretation of previously obtained spin-lattice relaxation times of the vinyl carbon peaks. The two vinyl groups are found to differ considerably in their motional correlation time.     

Molecular architecture and physicochemical properties of some vinyl alcohol-vinyl acetate copolymers

Two series of vinyl alcohol-vinyl acetate copolymers were prepared by homogeneous and heterogeneous acetylation of the same precursor poly(vinyl alcohol). Their intramolecular monomer distributions were analyzed by IR spectrometry, calorimetry, and differential thermal analysis. The results show a more blocky distribution for the heterogeneously prepared copolymers. The properties of these (co)polymers in dilute aqueous solution were determined by means of viscometry. Whereas the copolymer-solvent interaction parameter of the homogeneously acetylated, random copolymers hardly varied with acetate content, a definite minimum was found for the blocky copolymers at about 7 mole% vinyl acetate. These findings were attributed to the incompatibility of dissimilar sequences, which sharply decreases with decreasing vinyl acetate sequence length. Up to about 17 mole% vinyl acetate content, the solvent quality for the copolymers is at least as good as for poly(vinyl alcohol). In addition, the dilute solution properties of the samples were established in water saturated with 1-butanol. For copolymers with up to about 17 mole% vinyl acetate, at 25°C this mixture is a better solvent than water. The highest increase in solvent quality was found for the homopolymer, whereas the increase diminished with acetate content, irrespective of the intramolecular vinyl acetate distribution. These findings are explained in terms of preferential adsorption of 1-butanol onto the (co)polymer backbone due to hydrophobic interactions and prevention of this process by the bulky acetate groups.