13C-Nuclear Magnetic Resonance Analysis of Some Essentially Random Copolymers of Methyl Methacrylate and Butadiene

20 MHz ¹³C-NMR (nuclear magnetic resonance) spectroscopy has been used to determine the relative concentrations of certain methacrylate and butadiene containing monomer sequence fractions in some essentially random free-radical copolymers of methyl methacrylate and butadiene. Several of the results are in good agreement with those obtained in an earlier ¹H-NMR study and confirm, within experimental error, that the copolymeriza-tion obeys first-order Markov statistics. The patterns of olefinic carbon resonances reveal that the progressive introduction of methacrylate units into the polymers slightly increases the trans-1,4- to cis-1,4 ratios of the butadiene units relative to that found for a pure polybutadiene prepared under similar conditions.     

Microstructures of a Hydrogenated Styrene-Butadiene Copolymer by 13C NMR

Abstract

The microstructure and sequence distribution of a styrene-ethylenebutene-1 copolymer obtained by quantitative hydrogenation of emulsion styrene-butadiene rubber (SBR) was determined using ¹³C NMR. The results show that the polymer has 82% (CH₂)_>6 units arising due to BBB', SBB and BBB triads (B = hydrogenated 1,4 butadiene, B' = butene-1 and S = styrene). The presence of long crystallizable methylene sequences results in a melting endotherm at 45°C for the hydrogenated SBR.     

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.     

Monomer distributions and number-average sequence lengths in hydrogenated butadiene–styrene copolymers from carbon-13 nuclear magnetic resonance

Monomer distributions and number-average sequence lengths are determined from ¹³C nuclear magnetic resonance (NMR) data for 1,4- and 1,2-butadiene additions and styrene additions in a series of four hydrogenated butadiene–styrene copolymers. The monomer distribution is expressed in terms of the six unique days from which it is possible to calculate the number-average sequence length of each monomer type. Carbon-13 NMR spectral assignments are given and the techniques for making the assignments are discussed. The method presented could, in principle, be applied to any copolymer or terpolymer. Limitations that are encountered in the analysis of hydrogenated butadiene–styrene copolymers high in 1,2 additions are discussed.     

Synthese de ligands de type amino-diphosphinites; etude en RMN 13C et 31P. Application a la dimerisation du butadiene par les complexes du nickel

The new chiral aminodiphosphinite ligands are readily prepared from chiral amino acids. These compounds were characterized by ¹³C and ³¹P NMR spectroscopy and their behaviour as homogeneous catalysts was investigated in the linear dimerization of butadiene.     

13C-Chemische verschiebungen und substituenteneffekte in polycyclisch konjugierten π-elektronensystemen mit fünf- und siebengliedrigen ringen1

In order to study the substituent influence on the ¹³C chemical shifts in polycyclic conjugated π-electron systems with five and seven membered rings we have studied the aceheptylene system with markedly alternating bond length— in contrast to azulene investigated earlier—as well as 5-azaazulene as a hetero-analogue of azulene. The substituent induced ¹³C chemical shifts Δδ_c observed in the monomethylazulenes, monomethylaceheptylenes and in 5-azaazulene are correlated with the atom-atom polarizibilities π_ij of the corresponding unsubstituted compound. For 5-aza-azulene it was further tested, if the ¹³C chemical shifts could be predicted using the ¹³C chemical shifts of 4-substituted derivatives (RCN, Cl, OEt) and the correlations given in the literature for the substituent induced ¹³C chemical shifts in the system benzene/butadiene. The results show that the influence of the π-electrons is markedly overshadowed in the methylazulenes and -aceheptylenes by other effects, but is clearly discernible in 5-azaazulene as a derivative of azulene; so the data can be used to predict the ¹³C chemical shifts of other azaazulenes.     

13C13C spin coupling constants in phenanthrene derivatives

The synthesis of six 1-X- (X = OH, OCH₃, OCOCH₃, CH₃, CHO and CN) phenanthrene derivatives with a ¹³C label at C-1 is described. An analysis of the ¹³C¹³C spin coupling constants shows the importance of π-interaction for the coupling constant transmission. Small ¹³C¹³C spin coupling constants over 6 bonds are reported.     

Comparison of methods of calculation of 13C-NMR chemical shifts of diene polymers with applications to isomerized natural rubber

Natural rubber was isomerized by two methods that involved either dehydrobromination of hydrobrominated natural rubber or heating natural rubber with butadiene sulfone. The ¹³C-NMR spectra of the methylene region of isomerized natural rubber was interpreted in terms of dyad arrangements for which assignments were made by calculating chemical shifts according to three different published methods. One method [Gronski, Murayama, Cantow, and Miyamoto, Polymer, 17 , 358 (1976)] gave the best overall agreement with the experimental chemical shifts; another [Sato, Ono, and Tanaka, Polymer, 18 , 580 (1977)] was better for C-1 and C-3 methylene carbon atoms; and still another [Khatchaturov, Dolinsky, Prozenko, Abramenko, and Kormer, Polymer 18 , 871 (1977)] gave results which deviated considerably from the other methods. From ¹³C-NMR intensity measurements it was shown that the elimination of HBr from hydrobrominated natural rubber occurred by a random process. Contrary to literature reports, it was found that the sulphur dioxide catalyzed isomerization of natural rubber was accompanied by a significant amount of double bond migration; a possible reaction scheme was proposed.     

Comprehensive 1H and 13C NMR assignment of 13 protobassic acid saponins

This study aimed to carry out complete ¹H and ¹³C NMR assignment of 13 protobassic acid saponins, including arganins A–C ( 1 – 3 ) and F ( 4 ), butyrosides B–D ( 5 – 7 ), tieghemelin ( 8 ), 3′-O-glucosyl-arganin C ( 9 ), Mi-saponins A–C ( 10 – 12 ), and mimusopsin ( 13 ), recorded in methanol-d₄. This was accomplished by the analysis of high-resolution one-dimensional (1D) NMR (¹H and ¹³C), two-dimensional (2D) NMR (¹H–¹H COSY, HSQC, and HMBC), and selectively excited 1D TOCSY spectra. Before this study, ¹H and ¹³C NMR data of arganins A–C ( 1 – 3 ) and F ( 4 ) were partially assigned. Our effort leads to their complete assignment, especially the glycon residue, and revises some reported data. Some revisions of the ¹H and ¹³C NMR data in the glycon part of butyroside C ( 6 ), tieghemelin ( 8 ), Mi-saponin A ( 10 ), and mimusopsin ( 13 ) were made. Those data of butyrosides B and D ( 5 & 7 ) and Mi-saponin B ( 11 ), which had not been recorded in methanol-d₄, are provided. In addition, the ¹H and ¹³C NMR data of Mi-saponin C ( 12 ) are reported for the first time. These data, being recorded in methanol-d₄, should be more friendly for use as a reference for identifying the related triterpenoid saponins.     

Substituent effects on 13C?13C coupling constants and chemical shifts in 13C labelled polycyclic aromatic hydroxy compounds

The effects of an hydroxy substituent on ¹³C? ¹³C coupling constants and ¹³C chemical shifts have been measured in 1-hydroxynaphthalene-2-¹³C and 1-hydroxypyrene-1-¹³C. The changes observed in the ¹³C? ¹³C couplings show the effect of a substituent attached directly to the labelled carbon or to a carbon ortho to this. In both situations the effect is a decrease in the numerical magnitude of most of the long range ¹³C? ¹³C coupling constants.     

13C-13C spin-spin coupling constants in the spectra of monosubstituted pyridines

The ¹³C- {¹H} NMR spectra of pyridine and a number of monosubstituted pyridines for compounds with the natural percentage of the ¹³C isotope were analyzed. The direct, geminal, and vicinal ¹³C-¹³C spin-spin coupling constants (SSCC) were determined. Linear relationships that link the ¹³C-¹³C SSCC in the spectra of monosubstituted pyridines and benzenes were obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1383–1385, October, 1985.     

13C-NMR-spektren und dynamisches verhalten von olefin- sonitril-eisendicarbonyl-komplexen.

The ¹³C NMR spectra of the isonitrile complexes olen fe(CO)₂CNR (R = Me, EMe₃; E = Si, Ge, Sn) with butadiene, penta- 1,3-diene, cyclohexa-1,3-diene, 2,3-dimethylbutadiene, cyclohepta-1,3-diene as olefiinic ligands indicate the fluctional behavior of these compounds in solution. At low temperature there is a conformative preference in all cases so that one CO group occupies the apical position of a square pyramid whereas the isonitrile ligand together with a CO and the olefin part are in the basal positions. Depending on te various olefin ligands and the CNR groups the pseudorotation process is dicussed on the basis of /gDG/DG values for the CO/CNR ligand exchange.     

Influence of polar modifiers on microstructure of polybutadiene obtained by anionic polymerization. Part 4: Acid-base polar modifiers forming σ-μ complexes: Amine-alkoxide,amine-ether-alkoxide,and ether-alkoxide

The influence of acid-base polar modifiers (σ-μ complex): amine-alkoxide, amine-ether-alkoxide, and ether-alkoxide complexes on microstructure of polybutadiene obtained by anionic polymerization was studied. The content of butadiene isomeric structures was determined based on FT-IR-ATR, ¹H, and ¹³C NMR data analyses. The results obtained indicated a very similar influence of all types of polar modifiers forming σ-μ complex on polymer microstructure leading to high vinyl polybutadiene with nearly equal ratios of cis-1,4 and trans-1,4 butadiene isomeric structures.     

Application of biosynthetic 13C-enrichment using [1-13C]-, [2-13C]- and [1,2-13C2]-acetate as precursor for 13C NMR spectral assignment of higher plant metabolites. The assignments of some bryonolic acid derivatives

The ¹³C NMR spectra of some derivatives of bryonolic acid (1) (D:C-friedoolean-8-en-3β-ol-29-oic acid) were assigned by means of ¹³C-enrichment, lanthanide-induced shifts (LIS) and comparison of chemical shift data between derivatives. The ¹³C-enriched species of 1, i.e., 1a, 1b and 1c were biosynthesized by Luffa cylindrica (Cucurbitaceae) callus fed with [1-¹³C]-, [2-¹³C]- or [1,2-¹³C₂]-acetate, respectively. Methyl acetylbryonolates 2, 2a, 2b and 2c, methyl bryonolates 3, 3a, 3b and 3c, methyl bryononates 4 and 4a, diacetyl-3β,29-diols (3,29-diacetyl-D:C-friedoolean-8-en-β,29-diol) 5, 5a, 5b and 5c, and 3-acetyl-3β,29-diols 6, 6a and 6b were prepared from 1, 1a, 1b and 1c, and their ¹³C NMR spectra were recorded. The ¹³C concentration of the ¹³C-enriched species was high enough to exhibit the satellite peaks clearly, and the analysed data were very useful for this study. Thus, total assignments for 2, 3, 4, 5 and 6 were established. It was found that conversion of the methoxycarbonyl group at C-29 into an acetoxymethyl group caused complex changes in the chemical shifts of the C, D- and E-ring carbons and those of the methyl carbons linked to these rings.     

Direct measurement of 1J(13C13C) in coordinated double bonds

¹J(¹³C¹³C) has been determined in naturally abundant samples of η¹,η² -alkenyl-η⁵ -cyclopentadienylnickel complexes; for the coordinated double bonds ¹J(CC) lies between the value for free ethylene and cyclopropane, and therefore gives direct insight into the relevant bonding situation.     

13C-13C spin-spin coupling constants in six-membered ring azaaromatic compounds

The ¹³C-{¹H} NMR spectra of monomethyl substituted diazines, protonated at the picoline and 2-methylopyrimidine nitrogen atoms, have been analyzed, along with that of pyridine N-oxide and its 2-methyl derivatives protonated at the oxygen atom. Direct and vicinal ¹³C-¹³C spin-spin coupling constants (SSCC) have been measured. It was found that the ¹³C-¹³C SSCC in diazines follow additivity rules which are based on consideration of the number and mutual orientation or distribution of nitrogen atoms in the ring. It has also been demonstrated that increased direct ¹J_CC values involving methyl group carbon atoms in -positions to nitrogen atoms in the aromatic ring are due to effects associated with unshared electron pairs.Translated from Khimiya Geterotsiklieheskikh Soedinenii, No. 9, pp. 1243–1250, September, 1988.     

13C,13C coupling constants of conjugated dienes

One bond ¹³C,¹³C- and ¹³C,¹H-coupling constants have been measured for some 1,2-dimethylene-cycloalkanes, as well as for 2,3-dimethylbuta-1,3-diene and methylenecyclobutane. The results for 2,3-dimethylbuta-1,3-diene confirm the findings for buta-1,3-diene, i.e. that J(C-1, C-2) is smaller for the diene than for the correspondingly substituted monoene. No differences have been found between the ¹J(CC) exocyclic coupling constants of the dimethylene and monomethylene cycloalkanes.     

Influence of polar modifiers on microstructure of polybutadiene obtained by anionic polymerization. Part 3: Lewis acid alkoxide (μ) and Lewis base amine,amine-ether,and ether mixed-type (σ+μ) polar modifiers

The influence of mixtures of sodium mentholate (SMT) as a Lewis acid polar modifier and different Lewis base polar modifiers (amines, amine-ethers, ethers) on the microstructure of polybutadiene obtained by anionic polymerization was studied and compared to the influence of the same polar modifiers used separately. Detailed characterization of the polybutadienes in terms of the content and distribution of butadiene isomeric repeating units was performed by ¹³C NMR and supported by FT-IR-ATR and ¹H NMR data analysis. The results obtained indicated that the use of a mixture of Lewis acid and Lewis base in most cases enhanced formation of 1,2 butadiene structures in comparison to the Lewis bases used separately. However, application of a mixture of SMT and DTP resulted in lower vinyl content than when DTP was applied alone. It is worthwhile to note that the combination of a Lewis acid (SMT) and one of Lewis bases tested (DMEAEE) enabled obtaining very high vinyl polybutadiene (88% ¹H NMR, 96% ¹³C NMR).     

The structural dependence of 13C, 13C coupling constants in cyclopropanes

The smallest one-bond carbon—carbon coupling constants of cyclopropane derivatives have been measured for [1-¹³C]cyclopropane-1,1-dicarboxylic acid and cyclopropanecarboxylic acid. The ¹³C, ¹³C coupling constants of cyclopropylcarbinol have also been determined. The dependence of ¹J(CC) of the three-membered ring on different substituents and hybridization effects is evaluated. The carbon—carbon coupling constant of the unsubstituted cyclopropane is discussed on the basis of self-consistent perturbation theory (SCPT) and s character calculations (localized bond orbitals), and the results are compared with the experimental finding. It is shown that the ¹J (CC) can be interpreted by assuming a dual-pathway coupling mechanism.     

Copolymerization of 1,3-butadiene and styrene with a neodymium catalyst

Homo- and copolymerization of butadiene and styrene in the presence of the catalyst system Nd(octanoate)₃/CCl₄/Al(iBu)₃ (iBu: isobutyl) were investigated at 60°C in heptane as solvent. The initiating catalyst system is very effective in the polymerization of butadiene. However, the presented copolymerization of butadiene and styrene is only practicable when using a special addition order of the catalyst components and a prescribed ageing phase. Copolymers obtained from various monomer feed ratios were characterized by ¹H and ¹³C NMR spectroscopy and gel-permeation chromatography (GPC). The copolymer characteristics especially microstructure, molar mass and molar-mass distribution (MMD) are strongly dependent on the composition of the monomer mixture.