Carbon distribution nuclear magnetic resonance

Carbon-13 nuclear magnetic resonance was used to determine the molecular structure of four copolymers of vinyl chloride and vinylidene chloride. The spectra were used to determine both monomer composition and sequence distribution. Good agreement was found between the chlorine analysis determined from wet analysis and the chlorine analysis determined by the C nmr method. The number average sequence length for vinylidene chloride measured from the spectra fit first order Markovian statistics rather than Bernoullian. The chemical shifts in these copolymers as well as their changes in areas as a function of monomer composition enable these copolymers to serve as model... 

Schaefer J (1971) High-resolution pulsed carbon-13 nuclear magnetic resonance analysis of the monomer distribution in acrylonitrile-styrene copolymers. Macromolecules 4 107-10. 

Carbon 13 nuclear magnetic resonance can be used quantitatively in analyses of polymers to measure conveniently comonomer concentrations, average sequence lengths, run numbers and comonomer triad distributions. 

Carman,C.J., Wilkes,C.E. Monomer sequence distribution in ethylene-propylene elastomers. I. Measurement by carbon-13 nuclear magnetic resonance spectroscopy. Rubber Chem. Technol. 44,781-804 (1971). 

Carbon-13 nuclear magnetic resonance (NMR) spectroscopy represents the only direct method to analyze the polymer regio- and stereostructure (isotacticity level). The structural information derived from this technique is not limited to diads (sequence of two monomer imits) but generally includes triads or pentads and, in some cases, nonad or undecad levels have been reached, as well. Nevertheless, it is important to keep in mind that these values are only mean values referring to the whole polymer sample and, in some cases, they are not sufficient to discriminate samples with a different distribution of defects (see later). 

Carbon-13 nuclear magnetic resonance NMR) is important in imder-standing more detailed structural information in the backbone of the polyethylene sample. For example, l.T.DPE is produced commercially with either 1 -butene, 1 -hexene or 1 -octene as the comonomer. Copolymers with a low content of 1-olefin contain only isolated branches, however copolymers containing higher levels of comonomer (e.g., 2-20 mol%) contain a wide variety of complex sequence distributions making C NMR a particularly important characterization tool. Information into the sequence distribution of the comonomer in ethylene/1-olefin pentads provides data to determine the reactivity constants K, k, k and k, where e represents ethylene and h represents 1-hexene. 

Carbon-13 nuclear magnetic resonance (NMR) is the most useful method of assessing tacticity. By C-13 NMR it is possible to assess the different sequential distributions of adjacent configurational units that are called dyads, triads, tetrads and pentads. The two possible dyads are shown in Fig. 1.5. A chain with 100% meso dyads is perfectly isotactic whereas a chain with 100% racemic dyads is perfectly syndiotactic. A chain with a 50/50 distribution of meso and racemic dyads is atactic. 

One has seen that the number of individual components in a hydrocarbon cut increases rapidly with its boiling point. It is thereby out of the question to resolve such a cut to its individual components instead of the analysis by family given by mass spectrometry, one may prefer a distribution by type of carbon. This can be done by infrared absorption spectrometry which also has other applications in the petroleum industry. Another distribution is possible which describes a cut in tei ns of a set of structural patterns using nuclear magnetic resonance of hydrogen (or carbon) this can thus describe the average molecule in the fraction under study. 

Since about 1960 nuclear magnetic resonance (NMR) spectroscopy has become an important tool for the study of chain configuration, sequence distribution and microstructure of polymers. Its use started from early broad-line studies of the one-set of molecular motion in solid polymers and passed through the solution studies of proton NMR, to the application of the more difficult but more powerful carbon-13 NMR methods to both liquids and solids. 

Nuclear magnetic resonance spectroscopy of dilute polymer solutions is utilized routinely for analysis of tacticlty, of copolymer sequence distribution, and of polymerization mechanisms. The dynamics of polymer motion in dilute solution has been investigated also by protoni - and by carbon-13 NMR spectroscopy. To a lesser extent the solvent dynamics in the presence of polymer has been studied.Little systematic work has been carried out on the dynamics of both solvent and polymer in the same systan. 

When using the thermal process for the production of SCT pitch, the temperature and time are important process parameters. The higher the temperature used, the higher is the aromaticity and condensation of the aromatic rings. The average carbon and proton distributions (determined by Nuclear Magnetic Resonance Spectroscopy) of SCT pitches prepared by thermal process at 390°C and 430°C are presented in Table III. 

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