Comparison of the configuration of β‐1,4 linked hexosans and wood xylan pentosans by means of the eizner‐ptitsyn viscosity equations

Abstract

The Porod‐Kratky persistence lengths, monomer and polymer radii, and Flory coefficients of a number of β0–1,4 linked hexosans have been compared to each other and to the β‐1,4 linked xylan pentosans of wood by applying the Eizner‐Ptitsyn viscosity equations to intrinsic viscosity and molecular weight analyses from a number of sources. The analyses were made on fractions of cellulose acetate, cellulose nitrate, cellulose caproate, the diethylacetamide derivative of cellulose xanthate, cellulose in cadoxene and in the alkaline ferric tartrate solvent, FeTNa, the galactomannan triacetate of guar, and the glucomannan triacetate of orchid salep tuber. Xylans from spruce and birch, polystyrene, and a branched dextran were also investigated. The persistence lengths of the hexosan derivatives, except the cellulose trinitrate, were remarkably similar and were found to vary from 48 A. for the cellulose caproate determined under theta conditions to 58 A. for the galactomannan triacetate. The persistence lengths of cellulose in the two complexing solvents (72 A.) were nearly identical, confirming that these solvents do not increase the solution dimensions of cellulose greatly. The configuration of the polymers were ranked on a common graph by plotting the log of the polymer radii to contour length ratios vs. the log of the contour length. The investigation shows that the 0–1,4 linked hexosans have a common configuration which is independent of the length of the derivative side group or of single α‐1,6 linked side groups, as in the galactomannan. The configuration of the hexosans is also independent of whether the main chain is composed of glucose or mannose, or a mixture of these sugars. The greater rigidity of the hexosans, in comparison to the pentosans, is explained in the former by hindrance between the C2 group of the one sugar with the C6 group of the next, which is absent in the pentosan that has no C6. Analogy is made to the hindered racemization in substituted biphenyls to explain the great rigidity of cellulose trinitrate, whose persistence length is 132 A.

Conformational analysis of xylan chains

“…In addition, the predicted value is lower than those estimated for cellulose and mannan of about 100 Å , as observed experimentally. 35 As suggested by the conformational analysis of the dimers, lack of the hydroxymethyl group increases the accessible conformational space of the glycosidic Table 2. Helical, structural and energetic parameters of the helical conformations of native and substituted xylan build from the geometries of the proposed crystal structures of xylan and from the geometries of the energy minima of the disaccharides reported in Table 1 Helix bonds, the corresponding polymer has a worm-like appearance.…”

Neutral polymer slow mode and its rheological correlate

“…HPC is a β‐1,4‐linked propyl‐substituted neutral polysaccharide. Its chains are relatively stiff, with a persistence length of approximately 100 Å 1–3. Aqueous HPC has a liquid–liquid crystal phase transition, but only at concentrations far above those studied here.…”

5. Polyoses (Hemicelluloses)

“…Additionally the xylan chains are more flexible than hexosan chains because of the lack of a CH20H-group (C6) (Swenson et al 1965;Wikström 1968). Additionally the xylan chains are more flexible than hexosan chains because of the lack of a CH20H-group (C6) (Swenson et al 1965;Wikström 1968).…”