Degree of substitution determinations

DE) amd from Polysciences, Inc. (Waurrlngton, PA). Tadsle I summarizes the saunple designations, nomlnaa degree of substitution, and actual degree of substitution (determined by potentlometrlc titration). 

Degree of substitution determined by H-NMR spectroscopy after perpropionylation [39]. 

Methyl cellulose n. A cellulose ether in which some of the cellulosic -OH groups have been replaced by -OCH3. The degree of substitution determines properties and uses as thickeners and emulsifiers. Commercially, a granular, white, flakey material, which acts as a water-soluble thickener and stabilizer used in water-based paints. 

The data in Table I indicate that the chromophores in the model compounds are very sensitive to environment. The solvent has a great effect on the wavelengths of maximum absorption and emission both when the chromophores are in the model systems and attached to the polymer chains. If the small bathochromic shift determined in dilute solutions which occurs when the chromophore is attached to a polymer is ignored, it is then possible to estimate the degree of reaction of the corresponding aldehydes with the parent polymer. The degree of substitution determined in this... 

Sodium carboxymethyl cellulose [9004-32-4] (CMC) and hydroxyethyl cellulose [9004-62-0] (HEC) are the ceUulosics most widely used in drilling fluids (43). CMC is manufactured by carboxymethylation of cellulose which changes the water-insoluble cellulose into the water-soluble CMC (44). Hydroxyethyl cellulose and carboxymethyl hydroxyethyl cellulose (CMHEC) are made by a similar process. The viscosity grade of the material is determined by the degree of substitution and the molecular weight of the finished product. 

Determining the degree of substitution using standard proton nmr refles on the integral ratio between the ceUulosic ring protons ( i 5.0-2.96) and the ester alkyl protons ( i 1.26 for butyryl and propionyl and i 2.06 for acetyl methyl groups). This simple procedure is used extensively to determine the extent of esterification and is currently the fastest, easiest way for determining the DS of mixed cellulose esters. 

Therefore a fully substituted derivative would have a degree of substitution of 3.0 whilst a cellulosic material in which on average 1.8 hydroxyl groups per glucose unit had been replaced would have a degree of substitution of 1.8. Commercial derivatives usually have a degree of substitution of less than 3.0, the actual value chosen being determined by the end-use. 

Whereas mechanical properties are largely determined by chain length, the softening point, hardness, water absorption and solubility are rather more determined by the degree of substitution (see Figure 22.6). 

The degrees of substitution have been determined by elemental analysis of the remaining Cl and C contents and by 1H NMR according to the integration of the different peaks observed. The 1H-NMR spectra have been recorded at 60 MHz in( CD3COCD3 at 27°C ... 

The 1H NMR spectra have been used by dos Santos et al.30 in determination of the degree of substitution (DS) in chitosan Schiff bases. The DS was found from the ratio between integrations of signals... 

Zhao, H., and Heindel, N.D. (1991) Determination of degree of substitution of formyl groups in polyaldehyde dextran. Pharm. Res. 8, 400M02. 

Polymer Solubility. The modified polymers were soluble in DMSO, dimethylacetamide, dimethylformamide and formic acid. They were insoluble in water, methanol and xylene. Above about 57% degree of substitution, the polymers were also soluble in butyrolactone and acetic acid. Solubility parameters were determined for each polymer by the titration procedure as described in the literature (65). The polymer was dissolved in DMSO and titrated with xylene for the low end of the solubility parameter and a second DMSO solution was titrated with water for the high end of the solubility parameter range. These solubility parameters and some other solubility data are summarized in Table II. 

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. 

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