Spectra polypropylene

It will be apparent from the above discussion that a satisfactory set of assignments has not yet been achieved for the polypropylene spectrum. In most cases this is because the basic nature of the mode is unknown. Studies on partially and fully deuterated polypropylenes would answer these questions, and will clearly have to be undertaken in order for the final results to be more certain. When this has been done it should then be possible to evaluate more meaningfully the significance of the deviations between the observed and calculated I Ie ratios. As we have noted, these ratios are determined by the structure, if we make simple assumptions about the group transition moment directions. The deviations imply that either these assumptions are not valid or that the structure requires... 

The FT-IR-ATR absorption spectrum of the control polypropylene (untreated) is shown in Figure 1. It is a typical polypropylene spectrum with absorption bands due to asymmetric and symmetric stretching of CH3 and CH2 groups around 2900 cm-1. The absorption bands at 1460 nd at 1380 cm-1 represent the asymmetric and symmetric bending of CH3 respectively. Absorption bands at 2878 cm-- - (CH3 stretching) and at 841 cm-- (Methylene rocking modes) suggest that the polypropylene membrane is of the isotactic form. 

Molecular secondary ions under rare gas primary ion bombardment are used for compound Identification and to obtain structural and chemical information. Each compound gives rise to a characteristic fragmentation pattern ("fingerprint spectrum") under a given set of analytical conditions which can permit sample identification by comparison with the mass spectra of known compounds. For instance. Fig. 20 illustrates that the fingerprint spectra of two closely-related polymers are sufficiently different to permit distinction to be drawn. In particular, the polypropylene spectrum is distinguished by the relatively intense CcHg+ ion at m/e = 69. If the... 

Fig. 4.19. Difference spectra characteristic of the amorphous phase of quenched isotactic polypropylene (spectrum a) and of the ordered phase of the annealed sample (spectrum b). (Reproduced with permission from Ref. [19] 1977 Butterworth-Heinemann, Ltd.).

Figure 6 Vibrational spectra of polymers, (a) Transmission infrared spectrum of polyethylene (b) electron-induced loss spectrum of polyethylene (c) transmission infrared spectrum of polypropylene. ...

Upon photolysis of polypropylene hydroperoxide (PP—OOH) a major absorption at 1726 and 1718 cm has been observed in the IR spectrum, which is attributed to the carbonyl groups. Sometimes the macroradical having free radical site reacts with a neighboring newly born hydroperoxide causing the formation of a macroalkoxy radical [116]. 

Figure 5. (a) The ( A, SO,) anion symmetric streching mode of polypropylene glycol)- LiCF,SO, for 0 M ratios of 2000 1 and 6 1. Solid symbols represent experimental data after subtraction of the spectrum corre-ponding to the pure polymer. Solid curves represent a three-component fit. Broken curves represent the individual fitted components, (b) Relative Raman intensities of the fitted profiles for the ( Aj, SO,) anion mode for this system, plotted against square root of the salt concentration, solvated ions ion pairs , triple ions, (c) The molar conductivity of the same system at 293 K. Adapted from A. Ferry, P. Jacobsson, L. M. Torell, Electrnchim. Acta 1995, 40, 2369 and F. M. Gray, Solid State Ionics 1990, 40/41, 637. 

Fig. 21.11. Mass spectra of the unknown off-flavor compound after spectral subtraction from the co-eluting peak and the matching spectrum from the NIST library. (Redrawn/redrawn from J. Chromatogr., 351, R.A. Sanders, and T.R. Morsch, Ion profiling approach to detailed mixture comparison. Application to a polypropylene off-odor problem, 525-531, Copyright (1986) with permission from Elsevier.)...

Crystallinity. Is one of the key factors influencing properties. You can think of crystallinity in terms of how well a polymer fits in an imaginary pipe, as in Figure 22-6. Linear, straight chains are highly crystalline and fit very well. Bulky groups, coiled chains, and branched chains are not able to line up to fit in the pipe. They are amorphous, the opposite of crystalline. In a spectrum from totally amorphous, to almost totally crystalline, there is methyl methacrylate, polypropylene, low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and nylon. 

Thermal stability. The presence of side chains, cross-linking, and benzene rings in the polymer s "backbone increase the melting temperatures. For example, a spectrum of polymers with increasing melting temperatures would be polyethylene, polypropylene, polystyrene, nylon, and polyimide. 

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... 

Under analogous conditions the spectrum of syndiotactic polypropylene is clearly distinguishable from that of the isotactic polymer but it, also, suffers from the same limitations. In both polymers it is difficult to determine the degree of stereoregularity with any accuracy. 

Interpretation of the spectrum has been accomplished very neatly by two different methods. Stehling and Knox (105) examined samples of both isotactic and syndiotactic polypropylenes that had been slightly epimeiized by a radical... 

Figure 7. Methyl region of 50.3 MHz C NMR spectrum of atactic polypropylene ran at 100°C.

A deeper understanding of the NMR spectrum of polypropylene was obtained through the use of hemiisotactic polypropylene, 58, already mentioned (101). The strictly limited number of sequences (see Tables 2 and 5) greatly simplifies the spectrum, eliminating the major part of peak overlapping, especially in the methyl region furthermore, its high solubility permits the use of... 

Figure. 18. CP-MAS C NMR spectrum of crystalline syndiotactic polypropylene in the helical conformation. From (243) Copyright Chem. Soc., London.

As an example chosen in the macromolecular field the C NMR spectrum of syndiotactic polypropylene might be mentioned In solution (averaged random coil conformation, molecular model corresponding to 7) it presents three signals in the crystal state, where a chiral rigid conformation exists [(2/1)2 helix], it shows four signals (Figure 17). 

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