Infrared spectroscopy carboxyl groups, determination

Methods for determining carboxyl end-groups and hydroxyl end-groups in polyesters have been described in detail (77). Estimation of carboxyl end-groups by hydrazinolysis has been described by Zahn et al. (78). These authors also describe methods for analysis of comonomers in polyesters. Infrared spectroscopy has also been used for measuring end-group concentrations (108). DP determinations can be made from viscosity measurements in o-chlorophenol (109) or in phenoltetrachloro-ethane solution (50 50) (110). At times it may be sufficient to express results simply as relative viscosities (101). 

Fourier transform infrared (FTIR) spectroscopy is the most popular method for determining the imidization process in the solid state and identifying specific substituents on the macromolecular backbone (e.g., CN, SO3H, CO, SO2).131 A method for calculating the diermal imidization extent based on FTIR data has been reported by Pride.132 Raman spectroscopy was used on the model study of PMDA-ODA condensation, and the possible formation of an inline bond by reaction of an amino group with an imide carboxyle was evidenced.133... 

Vibrational spectroscopy is the method of choice for the characterizing functional groups in complex organic molecules. Infrared transmission spectroscopy has been used on dried humics pressed into KBr pellets to determine the relative carboxylate content of humic materials (14-16). However, interferences arise from the presence of water bands and possible alterations of the samples under the high pressures used to form the pellets. Diffuse-reflectance techniques can avoid some of the difficulties associated with the KBr pressed-pellet method (9,17-18). To obtain a spectrum analogous to an absorption spectrum, the data are transformed from reflectance units to Kebulka-Munk (K-M) units. However, K-M units are related to... 

Yates group [67] used IR spectroscopy, temperature-programmed desorption, and mass spectrometry to study Xe adsorption on purified and cut SWNTs. The nanotubes were cut by subjecting them to a mixture of sulfuric and nitric acid treatment, followed by sonication with sulfuric acid and peroxide. Infrared (IR) measurements determined the presence of carboxylic acid and quinone groups on the treated tubes. Mass spectrometry of treated tubes heated under vacuum determined the evolution of different groups from the tubes as the temperature increased (CH4, CO, H2, and CO2). 

The most important metal-containing heat stabilizers in PVC can also be identified through IR-spectroscopy (see Section 8.2). Characteristic absorption bands for the salts of carboxylic acids are the bands of the ionized carboxy group in the region from 1590 to 1490 cm and from 1410 to 1370 cm Since the exact position of the absorption bands depends mainly on the metal counterions of the carboxy group, the IR-spectra provide a first identification of these metals. Tin stabilizers also show characteristic bands in these regions of the IR-spectrum. To determine the spectra, one uses pressed pellets made by finely grinding the sample material with potassium bromide. The identification of the metal becomes even more certain if an FT-IR (Fourier Transform/Infrared) instrument is available. With such an instrument, it is possible to subtract the spectrum of an additive-free... 

Infrared (IR) spectroscopy is probably the quickest and cheapest of the spectroscopic techniques in determining the functional groups of the sample. The samples can be soUds, liquids, or gases and can be measured in solution or as neat liquids mulled with KBr or mineral oil. Comparison of IR spectra of substances of known structure has led to many correlations between wavelength (or frequency) of IR absorption and features of molecular structure. Certain structural features can easily be established. For example, in an organic compound that contains only C, H and O, the oxygen can only be present as C=0,0—H, or C—O—C or a combination of these, such as the ester or carboxylic acid group. 

Childs and Hardcastle [99] cocrystallized piroxicam with 23 different carboxylic acids by crystallization from solution and also by grinding, affording in total 50 unique piroxicam acid cocrystals. Where possible, the structure of cocrystals was determined from diffraction experiments (eight cocrystals), while the entire collection of cocrystals was additionally characterized by PXRD, infrared (IR) spectroscopy, and Raman spectroscopy. The structural study showed that the piroxicam is indeed present in both tautomeric forms in obtained cocrystals, as nonionized and zwitterionic form, and showed unique synthons for each tautomeric form (Scheme 13.16). These tautomeric forms were evident in Raman spectra, where the zwitterionic forms have a characteristic peak at 1410cm . The Raman spectroscopy further divided nonionized piroxicam cocrystals into two classes. This division was ascribed to different hydrogen bond interactions with the amide N-H group, which was also confirmed by structural investigations. 

So far it has been assumed, without any proof, that sulfonic groups in SPPO are attached to aromatic rings. In principle, sulfonic groups could also be attached to methyl groups as in case of other modified PPO polymers, for example, carboxylated PPO or methyl ester carboxylated PPO [22]. Acid-base and conductimetric titrations do not allow distinguishing between aryl and methyl substituted PPO. On the other hand, proton nuclear magnetic resonance ( H NMR) and infrared (IR) spectroscopy provide more information on the structure of SPPO. These techniques can also be used for determination of the DS of SPPO. 

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