Conformation cellulose derivatives

Finally it may be remarked that the dynamic viscoelastic properties of plasticized cellulose derivatives seem to give no evidence of any unusual temperature dependence of the chain conformations. Thus, Landel and Ferry (162, 163, 164) successfully applied the method of reduced variables [see, for example, Ferry (6)] to various concentrated solutions of cellulosic polymers, and found that the temperature reduction factors were quite similar to those for other flexible polymers such as poly(isobutylene). 

The cellulose derivatives E4M, E50LV, and F4M have shown different behavior at the air-water interface. E4M displayed the highest adsorption efficiency and surface activity, as could be determined from tensiometry and ir-A isotherms. E4M was found to adsorb fastest at the interface. The high hysteresis shown by E4M implies that it forms monolayers where molecules can be more compacted after compression and yet keep the acquired spatial conformation. 

The conformational distortions give rise to some flexibility of the molecules of cellulose derivatives. Tanner and Berry (1974) measured the mean square end-to-end distance of diacetate cellulose in trifluoroacetic acid... 

For all cellulose derivatives tested, a reduction of the zeta potential of the suspensions with increased polymer concentration is observed (Table 20). The effect of the molecular mass differs depending on the derivative concerned. For HEC and HPC, the amount adsorbed and the area per molecule decreased as the molecular mass increased, indicating a flatter adsorption conformation. For HPMC, the adsorption increased as the macromolecular chains became longer. Adsorption was maximum for the more hydrophobic HPC. 

Cellulose derivatives pack as sheet-like structures, for example, cellulose triacetate or butyrate as well as some ethers, e.g., trimethyl cellulose. Regio-selective derivatives of these mentioned esters or ethers placed at C2 and C3 with various other groups at C6 may belong to the same conformation class, that is, their conformation is determined by the substituent at positions 2 and 3. Many cellulose derivatives crystallize as rod-like helices of various kinds, e.g., 3/2,8/5, and these structures are also found in solvent built-in crystals. It should be mentioned that several cases are known where a change in conformation occurs if a polar solvent is built into the interstitial spaces between the polysaccharide chains. The sheet-like cellulose triacetate conformation converts to a rod-like 8/5 helix with nitromethane present. 

It should be emphasized that the compensation of the twist and changes in the pitch for statistically trisubstituted LC deriva-tive/solvent system, e.g., 3C1-CTC-CTC/ TRIMM, occur when no full turn of the conformational helix with one kind of substituent group most probably exists. At present, a suitable explanation cannot be provided for this behavior of lyotropic LC cellulose derivatives. 

The enthalpies of dilution of aqueous solutions of sodium chondroitin 4-and 6-sulphates have been reported. Chondroitin sulphate in aqueous solution may behave in such a way that the polyanion has a stretched conformation with disaccharide lengths of approximately 12.6 A at infinite dilution and a conformation similar to that of the solid state at moderate concentration. The decrease in viscosity of chondroitin 4-sulphate and hyaluronic acid in acid and neutral solutions resembles that of cellulose derivatives in both magnitude and sign. A new polymorph of sodium chondroitin 4-sulphate has been crystallized from an ethanolic aqueous solution at low pH. The unit ceU of the new polymorph is rectangular with dimensions in A of a = 16.0, b = 24.1, and c = 26.0. 

A number of cellulose derivates in various solvents was examined by Sakuraba and Lee, who also studied polychloroprene, polyvinylacetate and polystyrene in bemjene. In these cases the molecular weights were unknown, but it was shown by the following simple argument that the results obtained conform to equation (12). If the concentration is c grzmslcm, the solution contains... 

As regards the validity of Staudinger s viscosity rule, opinions are still at variance It is beyond all doubt that a number of cellulose derivatives conform closely... 

Chain conformations of a-and P-llnked glycan derivatives have been studied through CD. The studies suggested that a-llnked amylose tricarbanilate adopted a helical conformation, whereas the p-linked cellulose derivative did not. The CD spectra of these derivatives is shown in Figure 9.7. Frequent use of CD has been made to study not only the conformation of other polysaccharides but also their association in certain polysaccharide gels like alginate and pectin. 

Evidence for the involvement of salt links in the stabilization of bakers yeast jS-o-fructofuranosidase has been obtained from studies of immobilization of the enzyme on cellulose, derivatives of Sephadex and insolubilized con-canavalin A, and modification with citraconic anhydride, methyl acetimidate, or ethylene diamine. The general stability to such treatments was offered as the evidence, since modification of either amino- or carboxy-groups would result in loss of conformational stability, unless the stabilizing salt linkages were present. 

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