Spectra, polymer, interpretation

NMR spectrum of polyvinylidene fluoride as indicating the presence of about 10% of head-to-head units. It is difficult to believe, however, that "head-to-head units could occur in polytrifluorochloroethylene with the frequency which would thus be required. Such an explanation would also necessitate the assumption that the polytrifluorochloroethylene chain is either nearly completely isotactic or syndiotactic, for otherwise a large multiplicity of peaks arising from chain irregularity would be expected to appear, and the polymer spectrum would be more complex than is observed. There is no question as to the correct interpretation of the CFa resonance in the racemic and meso model compounds, and we believe that a corresponding interpretation of the polymer spectrum is by far the more plausible. However, a study of head-to-head model compounds would be required to establish this point with certainty. 

We will start by surveying the parameters that are used to describe the magnetic interactions within the nitroxide label, as well as the parameters used to characterize its motion. Because of the significant number of parameters that may be required to describe the rotational dynamics, the best means of extracting information about probe structure, orientation, and dynamics is to fit a calculated ESR spectrum to the experimental one by least-squares minimization of the model parameters. The chapter describes some of the least-squares methods that have been successfully applied to this type of analysis and concludes with some illustrative examples. Specific applications to spin-labeled polymers and interpretation of the ESR parameters obtained by this analysis are described in greater detail in Chapter 6. 

We shall discuss the interpretation of these results a little later. Let us first consider the interpretation of the atactic polymer spectrum (Fig. 3). This polymer was... 

The photoelectron spectra of pyridazine have been interpreted on the basis of many-body Green s function calculations both for the outer and the inner valence region. The calculations confirm that ionization of the first n-electron occurs at lower energy than of the first TT-electron (79MI21201). A large number of bands in the photoelectron spectrum of 3,6-diphenylpyridazine in stretched polymer sheets have been assigned to transitions predicted... 

The mass spectrum of polymeric sulfur S, prepared from either liquid sulfur or by extraction of commercial flowers of sulfur , has been measured and interpreted in terms of Ss, Sy, and Ss molecules leaving the polymer on heating and depolymerization [203]. This result is in agreement with depolymerization studies in solution which also show Ss and Sy as the major thermal degradation products [174]. 

Many biologically important sugars are derivatives having a chromophoric group that absorbs within the range of commercial instrumentation. Not only is the c.d. spectrum of such molecules easier to measure, but the interpretation of the spectrum is simplified, because only the chromophore is involved. Many laboratories have concentrated on the c.d. of such monomers and their polymers, and the results will be discussed. 

As in many other aspects of polymer stereochemistry, polypropylene also plays a central role in NMR spectroscopy. Since 1962 numerous articles have dealt with the interpretation of its proton spectrum (125-128) the state of knowledge at the end of that decade has been well described by Woodbrey (117). The difficulty in this study stems fiom two factors The narrow frequency range comprising the entire spectmm and the large homonuclear coupling between CH2, CH, and CH3 protons. The whole spectrum is within a range of <1.5... 

Following irradiation at low temperatures, the ESR spectrum of polymers shows changes in radical structure, ascribed to the movement of electrons and radicals to other and more stable sites. The behavior of many dried biological macromolecules is similar although a detailed interpretation may be more difficult. 

We therefore studied the effect of temperature and of concentration on the position of the hydroxyl peak in simple alcohols (methanol, ethanol, etc.) in the pure state, and in carbon tetrachloride or chloroform solutions. Some of the results of this work have already been reported [1]. A plot of peak position against concentration gives curves such as that in Fig. la. Interpretation of this type of curve from the N.M.R. data alone is impossible. It is clear that several different species (monomer, dimer, polymers) are contributing their effect, but because of the averaging phenomenon only a single OH peak, representing the weighted mean of all these species, is observed. We have now used infrared spectral data to clarify the situation. A careful examination of the infrared spectrum of all normal aliphatic alcohols... 

The first example to appear on dichroism in the Raman spectrum of oriented polymers concerned fibres and films of isotactic polypropylene (17). Unfortunately it was not possible to interpret the results because... 

Spectra have been recorded of the following polymers Poly isobutylene. Schaufele has reported a spectrum of a non-turbid specimen of this material complete with depolarization data (18). Bands at Av - 2919 and 720 cm 1 are clearly polarized and must result from symmetrical modes. Schaufele was also able to show that the short chain hydrocarbon CH3(CH2)12CH3 could be examined satisfactorily but the results were very much sharpened by cooling to liquid air temperatures. Polyisoprene and Polybutadiene. Both of these in the cis form have also been examined at Southampton very recently. The trans isomers gave no spectra due to fluorescence but no interpretation has been attempted as yet. Spectra are shown in Fig. 7 and 8. 

Primary alkyl isocyanides are known not to comply simply to homopolymerization. It was recently reported that polyisocyanides prepared with nickel(II) compounds varied in color from yellow to black (22,23). The latter occurred at preparative temperatures in excess of 25° C, or when polymer non-solvents or acids were used. Further, the addition of acids to solutions or suspensions of the yellow polymers also led to black compounds. The NMR spectrum of a soluble polymer sample (i.e. MVPO = 1100) of black poly(ethyl isocyanide) shows methylene resonance shifts to values as occur in nitriles, which were interpreted as giving evidence of rearrangement to a polycyanide... 

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