Structural characterization of 1,2-polybutadiene by 13C n.m.r. spectroscopy: 1. Signal assignment in hydrogenated polybutadienes

The configurational sequences of 1,2-unit in a series of hydrogenated syndiotactic 1,2-polybutadienes were investigated in relation to the sequence distribution of 1,2- and 1,4-units. The signals at 10.20–10.94 ppm were assigned to the methyl carbons in the isolated 1,2-unit, the 1,2-1,2 dyad sequence flanked by 1,4-unit, and the 1,2-1,2-1,2 triad sequence, in order of increasing magnetic field. The splittings due to the configurational sequences were observed in the signals, reflecting the dyad and triad sequences of the 1,2-unit, which were assigned by considering the relative intensity of the signals and also the chemical shifts of model polymers.     

Hydrogenation of low‐molar‐mass,OH‐telechelic polybutadienes. II. Nuclear magnetic resonance and infrared spectrometric determination of hydroxyl end groups before and after hydrogenation by diimide

¹H nuclear magnetic resonance (¹H‐NMR), ¹³C‐NMR, and infrared spectroscopies were used to determine concentrations (c_OH, in mmol/g) of the secondary hydroxyl end groups in the low‐molar‐mass, OH‐telechelic polybutadienes, and their hydrogenated analogs. Mean OH‐functionality (f_OH ≤ 2), that is, an average number of OH groups per one polymer chain, was calculated from c_OH for each sample and each method, and the results were compared with those obtained by a conventional acetic anhydride titration method. It has been found that with molar masses of the samples studied (2310 to 3410 g/mol), the differences between individual spectrometric methods are usually not higher than approximately 10%, which corresponds to an expected relative experimental error. Certain differences in f_OH between individual methods are discussed. No systematic change of f_OH after virtually total hydrogenation of the olefinic double bonds of the polymeric substrate by diimide was observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3214–3224, 1999     

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.     

13C n.m.r. study of the structure of poly(aspartic acid)

From hydrolysis of the product of thermal polycondensation of aspartic acid, poly(succinimide), under various conditions, a series of samples of thermal poly(aspartic acid) was obtained. These polymers differed by molecular mass and, from n.m.r. spectral evidence, by the contents of α and β peptide bonds, depending mostly on the pH of hydrolsysis. The contents of α and β bonds found were further confirmed by analysis of the n.m.r. spectra of the complex of poly(aspartic acid) with Co(II). Also, spectra of poly(aspartic acid) obtained by debenzylation of poly(β-benzyl-l-aspartate) described in our previous work were analyzed in greater detail. A comparison of racemic and optically pure polymers has shown that the n.m.r. spectra are only slightly affected by stereoregularity, and that stereoregularity is not the cause of the splitting of the various carbon bonds. Analysis of the complicated structure of the spectra, mainly of the carbonyl group, leads us to the conclusion that the distribution of the α and β bonds is random in all the polymers studied.     

H n.m.r. study on the sequence length of polysulphide linkages in the copolymer of chloroprene and sulphur

The sulphur rank distribution and the structures of chloroprene units in the chloroprene-sulphur copolymer have been investigated in detail by proton nuclear magnetic resonance spectroscopy (¹H n.m.r.). Two factors, the sulphur rank and the structures of chloroprene units, which complicate the spectrum, were elucidated by modification of the copolymer structure through partial and full reductions of the polysulphide linkages. The populations of the chloroprene units with different structures adjacent to the sulphur units were found to be different from those of the homosequence. It was found that the major sulphur unit in the copolymer is octasulphide, the next disulphide and the least common are the other polysulphides composed of 3–7 sulphur atoms. No evidence of monosulphide was found.     

13C Nuclear Magnetic Resonance Studies of Phenol-Formaldehyde Resins and Related Model Compounds 2 - Analysis of Sequence Structure in Resins

The paper reports ¹³C nuclear magnetic resonance spectra of novolac resins and the variation of the composition of the reaction mixture during the in situ preparation of resin. It is observed that in the initial stages of the reaction ortho substitution occurs; however the hemiacetal rather than the methylol derivative is observed. These methylol substituted intermediates are highly unstable and a better appreciation of the relative rates of structure formation can be obtained from an analysis of the methylene bridge region, para-para Bridges are the first to appear, the next are the ortho-para and finally the ortho-ortho linkages are observed. Analysis of the relative intensities of ortho and para bridge carbon atoms allows identification of the isomeric composition of the final resin. The proportion of each isomer depends on the catalyst used in synthesis of the resin.     

Structural characterization of Saudi Arabian medium crude oil by n.m.r. spectroscopy

Saudi Arabian medium crude oil has been characterized by ¹H and ¹³C n.m.r. spectroscopy. Several structural parameters such as the percentage of aliphatic carbons, aromatic carbons, n-alkanes, naphthenes, branched alkanes and chain length of paraffinic chains were calculated. The aromatic carbons were further classified as those attached to a hydrogen, methyl or alkyl group, or bridgehead carbons.     

Anionic polymerization of isoprene by the complexes oligoisoprenyllithium/tertiary polyamines in cyclohexane: 3. Structural study of the polymers by 1H n.m.r. at 100 MHz

The microstructure of polyisoprene prepared anionically in the presence of catalytic amounts of N,N,N′,N′-tetramethylethylenediamine (TMEDA) and pentamethyldiethylenetriamine (PMDT) has been studied as a function of $\text{r =}\text{[}\text{TMEDA}\text{]}\text{[}\text{living ends}\text{]}$ and $\text{r =}\text{[}\text{PMDT}\text{]}\text{[}\text{living ends}\text{]}$. No significant effect is observed for r ? 0.5. The structure varies drastically for r > 0.5. The 4,3 addition increases mainly at the expense of the cis4,1 addition and a plateau is reached for r ? 1.0. The results are discussed on the basis of the nature of the living species.     

Structural characterization of Saudi Arabian heavy crude oil by n.m.r. spectroscopy

Saudi Arabian heavy crude oil was separated into six fractions, including five distillate fractions (<93, 93–204, 204–260, 260–343 and 343–454 °C) and a >454 °C distillation residue. Each fraction was analysed by ¹H and ¹³C n.m.r. spectroscopy, and combined gained information from these analyses provided reliable average structural parameters. These included estimation of aliphatic and aromatic content, average paraffinic chain length, and estimation of hydrogen, methyl and alkyl bearing aromatic carbons for each of the six fractions. The extent of branching in paraffinic chains and amount of aromatic bridgehead carbons were also calculated.     

红外和核磁共振法鉴定聚醚型聚酯的组成结构

利用红外吸收光谱及核磁共振波谱仪的一维和二维技术对一种未知聚合物试样进行鉴定。由核磁共振二维技术分析得出聚醚酯的序列结构及其分布。结果表明:该未知聚合物试样为聚醚酯弹性体,由对苯二甲酸、间苯二甲酸、新戊二醇、乙二醇、聚四氢呋喃醚共聚而成。     

1H n.m.r. spectroscopy of the complexation of polybutadienyllithium by N,N,N′,N′-tetramethylethylenediamine

Partially deuterated oligomeric butadienyllithium was prepared both by capping a d-6 chain with d-4 monomer (1,1,3,4-tetra-deuterobutadiene) and by direct oligomerization of the d-4 monomer. The initiator, sec-butyllithium, was used at low concentration to minimize the level of vinyl addition and the N,N,N′,N′-tetramethylethylenediamine (TMEDA) was added only after polymerization was complete. The introduction of TMEDA causes the γ proton resonances of the allylic carbanion to move upfield and the β resonances downfield, corresponding to an increase in the extent of charge delocalization. With ratios of TMEDA: Li below 1:1 the carbanions having the cis conformation are complexed preferentially.     

Structural characterization of non-reductively ethylated coal by 13C and 1H n.m.r.

A major portion of some coals can be solubilized by non-reductive ethylation. A part of the solubilized portion of a bituminous highly caking coal was studied by ¹H and ¹³C nuclear magnetic resonance techniques. It was demonstrated that important structural information can be obtained by this method for the original insoluble material in coal. It was found that, in the investigated coal, about 40% of the aromatic carbon atoms are protonated and that 6–10% of total carbon atoms existed in original coal as active sites that were amenable to ethylation.     

Molecular motion of syndiotactic poly(α-methylstyrene) in solution studied by carbon-13 n.m.r. relaxation measurements

The carbon-13 n.m.r. spin-lattice relaxation times, nuclear Overhauser enhancement factor (NOE), and line widths have been measured for a syndiotactic poly(α-methylstyrene) in solutions in toluene-d₈ and o-dichlorobenzene-d₄ as a function of temperature from 40° to 163δC. The single correlation time model of relaxation is inadequate to explain the data of spin-lattice relaxation time and NOE. But, within experimental error, these relaxation data in two solvents over a full temperature range can be interpreted in terms of either the Cole-Cole or the log-χ² distributions of correlation times, or a conformational jump model proposed by Monnerie et al. The internal rotation of the methyl group is relatively rapid, while that of the phenyl ring is slow and practically overshadowed by the backbone segmental reorientation over the temperature range examined. The solvent dependence of relaxation data was discussed.     

High resolution solid state 13C n.m.r. of butadiene grafted polypropylene

¹H dipolar decoupled ¹³C n.m.r. experiments with the aid of the magic angle spinning technique have been used to determine the graft content and the isomer content of the polybutadiene grafts in a graft copolymer with isotactic polypropylene.     

Configurational structures of lactic acid stereocopolymers as determined by 13C{1H} n.m.r.

Investigations are made of the ¹³C{¹H} n.m.r. spectra of a series of poly(lactic acid) stereocopolymers obtained by different means, i.e. ring-opening polymerization of l-, rac- and meso-lactides initiated by powdered Zn, or copolymerization of l- and rac-lactides in different proportions, or condensation polymerization of rac-lactic acid. Resonances arising from the stereosensitivity of the carbonyl carbon atoms have been resolved using the resolution enhancement technique. The fine structures thus obtained are discussed in terms of configurational sequences. Comparison is made of the peak intensities with theoretical stereosequence distributions obtained when assuming single and pair additions of repeating units according to the Bernoullian statistics. Neither of the models for triad, tetrad and pentad stereosequences agrees with the area of the experimental lines. It is shown that redistribution of stereosequences in poly(lactic acid) occurs because of transesterification at the ester bonds in the melt. The final stereosequence distribution in the polymers obtained by ring-opening polymerization of lactides is discussed in relation to the pair-addition mechanism and to the redistribution due to transesterification reactions.     

The tacticity of poly(tri-n-butyl tin methacrylate) determined by 13C n.m.r.

The tacticities of poly(tri-n-butyl tin methacrylate)s prepared with radical initiators at various temperatures have been measured by ¹³C n.m.r. As expected, the polymers are predominantly syndiotactic and this syndiotacticity decreases with an increase in temperature. The activation parameters governing the tacticity are similar to those published for poly(methyl methacrylate) but differ somewhat from values published for poly(trimethyl tin methacrylate).     

N.m.r. study of cellulose-water systems: Water proton spin-lattice relaxation in the rotating reference frame

A pulsed n.m.r. study of relaxation in the rotating reference frame was performed on cellulose samples with moisture contents (MC) ranging from 20.5% to 218%. The dependence of the spin-lattice relaxation time (T_1ρ) in the rotating frame on temperature in a sample hydrated to approximately the fibre saturation point (FSP) indicates that in this case water exists in two different environments or phases. The first phase consists of a small number of water molecules (<1% of adsorbed water molecules in sample) tightly bonded to cellulose whereas the second phase consists of the remaining adsorbed water molecules which are more loosely attached. At room temperature exchange occurs between these phases at an intermediate exchange rate. For samples with MC >FSP a third water phase was identified. From the dependence of T_1ρ on the rotating field strength information about water molecule dynamics was deduced.     

Quantitative valuation of composition in vinylformal,vinylacetate and vinylalcohol ter-copolymers by1H- and13C-n.m.r. spectroscopy

The¹³C-n.m.r. signals were assigned to the composing structural groups of the copolymers. The composition of the copolymers was determined by¹³C n.m.r. using the NOE extinction technique. The analyzed samples were synthesized under normal and relatively mild reaction conditions. Despite this and purification methods that avoided elevated temperatures, it was not possible to find hemiformal groups in any amount. Therefore it is possible to analyze these copolymers composed of formal, vinylacetate and vinylalcohol structural groups in a relatively easy way by means¹H n.m.r.     

Carbon-13 nuclear magnetic resonance study of ethylene-1-octene and ethylene-4-methyl-1-pentene copolymers

Detailed assignments of ¹³C n.m.r. signals of ethylene-1-octene and ethylene-4-methyl-1-pentene copolymers, members of the linear low-density polyethylene (LLDPE) family, are presented. The equations relating signal intensities to the monomer sequences are given. Using these equations, the characterization of these copolymers by the triad monomer sequences is possible. From the analysis by the triad sequence, it is suggested that these 1-olefins have a tendency to be present isolated in the copolymer chain.     

Local composition heterogeneities occurring during crystallization in PVF2/PMMA blends as studied by high-resolution solid-state 13C n.m.r.

High-resolution solid-state ¹³C n.m.r. has been used to study the amorphous phase of PVF₂/PMMA blends. The decrease of the carbon magnetization as a function of the contact duration in a cross-polarization sequence was analysed in terms of the local composition heterogeneities occurring during PVF₂ crystallization. The influence of the composition and thermal history of the samples is discussed.