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Methylene bands, amorphous

Fig. 7. The infrared spectra of bile acids. (A) Cholanic acid, crystallized from a melt. (B) Lithocholic acid, Nujol mull. (C) Deoxycholic acid, Nujol mull—glassy amorphous melt. Asterisks indicate Nujol bands superimposed on methyl and methylene bands of lithocholic and deoxycholic acid. Fig. 7. The infrared spectra of bile acids. (A) Cholanic acid, crystallized from a melt. (B) Lithocholic acid, Nujol mull. (C) Deoxycholic acid, Nujol mull—glassy amorphous melt. Asterisks indicate Nujol bands superimposed on methyl and methylene bands of lithocholic and deoxycholic acid.
The band at 1303 cm"1 is reported to be one of the bands characterising the amorphous phase in PE. It follows that crosslinking causes a decrease in crystallinity. The band at 1411 cm 1 which is evidence for the occurrence of crosslinking due to the methylene... [Pg.177]

The absorption bands of interest in the IR spectrum of PE are in the region 1425-600 cm Crystalline and amorphous phases contribute to vibrations observed within these limits (62). Amorphous methylene wagging vibrations are observed at 1369, 1353, and 1303 cmThe broad peak at 1078 cm has been assigned to the C-S stretching vibration of the amorphous phase. [Pg.108]

The 725 cm" rocking mode doublet is presented in Figure 3. The peaks at 731 and 720 cm for this sample are approximately 15 times the intensity of the amorphous wagging modes. The 720 cm limiting frequency is assigned to long trans sequences in the amorphous and crystalline phases. For these samples, most of the methylene structures are in the crystal, and the band is associated with this phase predomi-... [Pg.108]

The amorphous methylene wagging bands show a temperature behavior which is more amenable to discussion. The 1352 cm" band has been calculated to result from the deformation of the methylene isolated by the GG conformation (55,56). The intensity of this band increased at elevated temperatures relative to the other amorphous wagging modes as a consequence of the higher energy of its conformation (55,56). This was also observed in the present work for the slow-crystallized sample. However, increases for the rapidly quenched systems only occurred after... [Pg.135]

A method has been developed which utilises a suggestion by Neilson and Holland [14], They associated the amorphous phase absorption of polyethylene at 1368 cm (7.31 pm) and 1304 cm (7.69 pm) with the trans-trans conformation of the polymer chain about the methylene group. Therefore the intensities of these two absorptions are proportional to one another. By placing an annealed film (approximately 254-381 pm) of high-density polyethylene in the reference beam of a double beam spectrometer and a thin, quenched film of the sample in the sample beam, most of the interference at 1368 cm (7.31 pm) can be removed. The method has the advantage that it is not necessary to have complete compensation for the 1368 cm (7.31 pm) band because... [Pg.354]

Polyethylene (PE) is the most-studied example of rotational isomerism. The crystalline domains are made up of the all-trans conformer structure. Bands that are characteristic of rotamers in the amorphous phase are also present. The most intense of the amorphous absorptions are the methylene wagging modes at 1303, 1353 and 1369 cm . The TG conformation is correlated with the bands observed at 1303 and 1369 cm . The 1353-cm absorption band is assigned to the wagging of the GG structure. When PE is heated through its melting point, the concentration of the TG and GG conformations increases. However, the concentration of the TG conformation increases well below the melting point, and this increase indicates the formation of localized conformational defects in the crystalline polymer. [Pg.168]

The band at 1378 cm is due to the methyl capped branches. Unfortunately, the methyl band at 1378 cm is badly overlapped by three interfering bands at 1304, 1352 and 1368 cm" that result from amorphous methylenes. The interference band at 1368 cm" is particularly strong. By using the spectrum of a linear polymethylene standard, it is possible to obtain a difference spectrum that isolates the 1378-cm band of the methyl branch for measurement of its absorbance. [Pg.172]


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Amorphous bands

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