SynopsisWater sorbence by saponified polyacrylonitrile-grafted polysaccharides was studied in relation to practical end uses. Graft copolymers prepared from wheat flour, corn flour, cotton wool, and rayon fibers swelled to a gel, exhibiting a 10-to 20-fold increase in sorbency over the starting materials. A further enhanced water capacity was obtained when homopolymer was not removed. Soaking the wheat flour copolymer in salts or dilute mineral acid nullified the enhanced water sorbence, which could be reversible restored by neutralization of acrylic acid functions with alkali. Swelling the copolymer in aqueous D-glucose did not impair its water capacity. The mechanism of swelling t o a gel appears to involve electrolyte osmotic pressure generated by a Donnan equilibrium. Grafting starch elevated its heat of water vaporization above that of pure water, and increased its capacity to absorb water from ethanol-water vapor at 40° above that of native starch. At higher temperatures, however, the dehydrating capacity decreased to that of native flour.

SynopsisThe endwise depolymerization (unzipping reaction) of hydrolyzed cotton cellulose ( x = 200) in water under a nitrogen atmosphere was followed a t 98OC at several alkalinities in the pH range of 8.0-10.5. The observed apparent first-order rate constant k l was invariable at low alkalinity (kl = ko), while above pH 8.5, kl increased with pH. The data conform with the expressionwhere [SH] denotes substrate concentration. The specific hydroxide ion catalysis is considered to involve ionization of the anomeric hydroxyl group at the reducing chain end that leads to elimination of the glucosidic oxygen atom bearing the polymer chain from C4 of the terminal D-glucose residue. In this initiation process, the glucosidic oxygen is eliminated as an anion so that rapid propagation of the unzipping along the polymer chain may occur. Thus, entire chains will depolymerize. The kinetic chain length Y is defined as the ratio k~: k t , where kt is the pseudofirst-order rate constant for chain terminations, and a value of Y -100 D-glucose residues was found at all the alkalinities investigated.

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(Amylodextrin) * 1,4-Glycans such as starch and cellulose depolymerize in hot alkaline solution from the reducing chain ends with sequential release of the monosaccharide residues as soluble saccharinate degradation products. The mechanism of this peeling or unzipping process involves a Lobry de Bruyn-Alberda van Ekenstein isomerization of the terminal D-glucose to an anionic 2,3-enediol residue, which undergoes a beta-alkoxy-carbonyl elimination of the shortened polysaccharide chain from C-4. Thus the reducing chain terminus is regenerated, bearing an anionic anomeric oxygen atom that facilitates propagation of the depolymerization along the molecular chain.2Measurements of the spectrophotometric properties of the iodine complex with amyloses after peeling did not detect a change in chain length.3 We therefore examined the molecular weight of the amylosic residues remaining after the alkali-catalyzed decomposition by measuring the viscosity of dilute aqueous solutions during capillary flow.After degrading amylose anaerobically in decimolar sodium hydroxide solutions for 3 hr a t 98°C to approximately one-half of the initial amount, the residual polymer was reprecipitated from the neutralized reaction mixture with acetone. The values obtained for the limiting viscosity number (intrinsic viscosity) (Table I) indicate that the average molecular weight of the amylose is reduced to 41% of its value when treated at 0.2% initial concentration and to 229' a t 0.5% concentration. This dramatic decrease may be accounted for a priori in several ways:

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