Cellulose specific rotation

Chromatography of a benzene solution of the low melting stilbene ozonide (mp 92°C) on finely divided cellulose-2 1/2-acetate, however, yielded fractions of the ozonide with specific rotation at 360 nm of -j-8.94° and —20.45°, respectively (5). This isomer, therefore, is the trans compound. Under the same conditions, the higher melting ozonide (mp 100°C) gave no fraction with optical activity, in agreement with its cis configuration. 

Optical Rotatory Power Measurement. Cellulose solutions were placed between microscope cover slips separated by a Parafilm spacer (thickness 0.127 mm). Optical rotatory measurements of the solutions were made with a Perkin-Elmer 241 polarimeter using a sodium light source (598 nm) and a mercury light source (356,436,546, and 578 nm). The specific rotation at a given wavelength of light [0] was calculated from the observed rotation 0 by... 

Figure 13. Specific rotation dependence at 25 C on solvent composition and on storage time cellulose concentration, 12g/100ml DP, 210 1 hour ( ), 24 hours (o), 213 hours (n).

The cellulose solution containing water (25.0/73.0/2.0) showed a more rapid increase in negative specific rotation with storage time compared with the solution prepared from solvent containing no water (25.5/74.5) (Figure 15). ... 

Lacroix et al. compared an HPLC with a H NMR method for quantification of the R-enantiomer in S-timolol maleate, a -blocking substance (Figure 6-7) [17]. For satisfactory resolution, the HPLC required the expensive cellulose tris-3,5-dimethylphenylcarbamate column (Chiracel OD-H), a mobile phase of 0.2% dimethylamine and 4% isopropano in hexane and H NMR (400-MHz) R-TFAE as a CSA in CDCIj. The resonance of the tert-butyl group between 1.0 and 1.1 ppm was used to measure the ee. With both methods, 0.2- 4.0% of the R-enantiomer in S-timolol could be determined precisely. Additionally, both methods (HPLC and NMR) were found to be superior to specific rotation, which is used in the USP XXIII for determination of optical purity. This superiority of NMR and HPLC methods over optical rotation has often been reported [2],... 

For a specific polymer, critical concentrations and temperatures depend on the solvent. In Fig. 15.42b the concentration condition has already been illustrated on the basis of solution viscosity. Much work has been reported on PpPTA in sulphuric acid and of PpPBA in dimethylacetamide/lithium chloride. Besides, Boerstoel (1998), Boerstoel et al. (2001) and Northolt et al. (2001) studied liquid crystalline solutions of cellulose in phosphoric acid. In Fig. 16.27 a simple example of the phase behaviour of PpPTA in sulphuric acid (see also Chap. 19) is shown (Dobb, 1985). In this figure it is indicated that a direct transition from mesophase to isotropic liquid may exist. This is not necessarily true, however, as it has been found that in some solutions the nematic mesophase and isotropic phase coexist in equilibrium (Collyer, 1996). Such behaviour was found by Aharoni (1980) for a 50/50 copolymer of //-hexyl and n-propylisocyanate in toluene and shown in Fig. 16.28. Clearing temperatures for PpPTA (Twaron or Kevlar , PIPD (or M5), PABI and cellulose in their respective solvents are illustrated in Fig. 16.29. The rigidity of the polymer chains increases in the order of cellulose, PpPTA, PIPD. The very rigid PIPD has a LC phase already at very low concentrations. Even cellulose, which, in principle, is able to freely rotate around the ether bond, forms a LC phase at relatively low concentrations. 

Specific inter- and intramolecular bonding are not necessary for ordered structures to persist in dilute solution. Ordered structures, that lead to highly asymmetric molecules, can be perpetuated by severe steric repulsions of substituents or an inherent restraint to rotations about single bonds. Such structures are known, even among synthetic macromolecules, and they form liquid-crystal systems. Some examples are polymeric aramides, poly(N-alkyl isocyanates) and some cellulose derivatives. 

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