Aliphatic C-H absorption

Polymer Structure. The reaction studied here is summarized in Equation 21. As shown in the experimental section, it is possible to prepare these polymers at various degrees of substitution. As the degree of substitution increases, the ratios of the infrared C=0/0H absorption peaks and the phenyl/aliphatic C-H absorption peaks increase in a linear manner (Table I). (It would be possible to determine the degree of substitution from such calibrated curves.) At the same time, the intensity of the OH band in the NMR spectra diminishes while a strong set of peaks due to the phenyl group forms. Elemental nitrogen analysis values for the modified polymers agree closely with the calculated values. In addition, the infrared spectra show the necessary carbamate N-H bands. These factors enable us to have confidence that the polymer structure is as shown in Equation 21. 

C—H Stretching Vibrations Tertiary C—H Groups Absorption resulting from this vibrational mode is very weak and is usually lost in other aliphatic C—H absorption. Absorption in hydrocarbons occurs near 2890 cm-1. 

This requirement has been met with soluble, pre-imidized polyimides. It has been found that secondary amines react quite readily with such polyimides in polar solvents such as N-methylpyrrolidinone or dimethylacetamide The reaction was done initially with morpholine for a series of available pre-imidized polymers (see Table I). The reaction was easily followed by infra-red spectroscopy (IR) (see Figure 2), the imide carbonyl absorptions at 1780 and 1723 cm 1 being replaced by amide carbonyls at 1645 cm1. In addition, the aliphatic C-H absorptions at 2880 cm 1 were noted. 

Two weak absorptions near 2850 and 2750 cm on right side of the aliphatic C—H absorptions. 

The subject of Figs. 4-6 involves another difficult topic the examination of carbonaceous materials. In order to obtain carbons prepared under controlled conditions, the pyrolysis of cellulose was studied. Fig. 4 shows just three of many spectra of pyrolysis sequences. The numerous changes in the spectra, e.g., the decline of aliphatic C-H stretching absorptions just... 

Figure 8.34 Strong, sharp absorption at 1700 cm 1 indicating a carbonyl group. No other significant patterns except the C-H pattern on the low side of 3000 cm . It is an aliphatic aldehyde or ketone. Figure 8.35 A benzene ring is indicated because of the band on the high side of 3000 cm-1 and the series of weak peaks between 1700 and 2000 cm . Aliphatic C-H bonds are also indicated (absorption bands on the low side of 3000 cm-1). Possibly ethylbenzene, or a similar structure.

For each alkylated extract, there was an absorption at 1700 cm which was absent in the untreated extract. This absorption may be attributed to esters that form from alkylation of carboxylic acids. This interpretation is consistent with the NMR analysis described below. For each O-alkylated extract, there was an increase in the intensity of the C-H absorption bands at 2800-3000 cm consistent with the introduction of aliphatic carbon. 

Formation of an amide is also indicated in the reaction of PCTFE with Cr(CO)6 and the primary amine, benzylamine. The infrared absorption spectrum shows an N-H stretch centered at 3400 cm, aromatic C-H stretches at 3063 and 3030 cm1, aliphatic C-H stretches at 2933 and 2876 cm1, a broad amide I/amide II band ranging from 1680-1580 cm1, and a C-N stretch at 1454 cm1. The C-Cl stretch at 970 cm1 also shows a significant decrease in... 

Photostabilization with Ultraviolet Absorbers. Absorption of ultraviolet light in the region 2900-3900 A. (290-390 m/x) results in the yellowing and loss in physical-mechanical properties of most polymers containing aliphatic C—H bonds. This degradation is usually a combination of ultraviolet absorption and oxidative attack (21). 

A regression analysis applied to a series of coals, chars, and tars with widely differing ratios of aliphatic-to-aromatic hydrogen has been used to calibrate the aliphatic and aromatic C-H absorption intensities. 

The absorption bands at 2920 and 2860 cm are evident in the spectra of most humic substances, usually superimposed on the shoulder of the broad O—H stretching band. They are generally more pronounced in humic acids than in fulvic acids. These bands are attributed to the asymmetric and symmetric stretching vibrations, respectively, of aliphatic C—H bonds in methyl and/or methylene units (Theng et al., 1966). This assignment is consistent with the observed increase in absorbance of these bands upon methylation of the humic substance (Wagner and Stevenson, 1965 Wershaw et al., 1981). 

The characteristic absorption bands in these spectra are almost the same and in agreement with the expected copolymeric structures (m = 1) [18]. However, the relative intensities of bands at 2880 and 2940 cm (aliphatic C—H bond) and 1250 cm (Si—Me bond) increase and those of 3040 and 3060 cm (aromatic C—H bond) decrease as m is increased. Obviously, this shows that the amount of [—Si(Me)2—] in the copolymer increases as m is increased. The X-ray diffraction powder patterns show that these copolymers are amorphous. The copolymers began to soften gradually from about 100°C. Differential thermal gravimetric analyses show that the copolysilanes began to decompose slowly at 280-300°C under nitrogen atmosphere. 

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