547.458.81 Dilute solutions of water-soluble cellulose esters and also solutions of model compounds -glucose and cellobiose -have been investigated. It has been shown that a definite influence on optical rotatory dispersion is exerted by the conformational difference of the pyranose rings of cellulose arising when the hydroxy groups in the macromolecule are partially replaced by functional groups of different natures.Optical activity characterizing features of the spatial structure of simple molecules was known even during the last century from the work of J. Biot, L. Pasteur, J. H. Van't-Hoff, A. M. Butlerov, and others. It is also known that features of the spatial structure of molecules determine various properties of a substance and play a major role in processes of synthesis.This question has been little studied as applied to cellulose and its derivatives. In the dissertation [1], which gathers together practically all the material on the optical activity of cellulose and celhilose acetate, there is no information on the connection of optical activity with the conditions of synthesis, the properties of the polymer, and the quality of the products. There are no clear ideas on the role of the functional groups of celhilose esters in the optical activities of their solutions.In order to elucidate the causes of the change in the optical activity of cellulose derivatives On the replacement of certain functional groups by others in the pyranose rings of the cellulose macromolecule, we have studied by the method of optical rotatory dispersion (ORD) dilute solutions of cellulose acetates (CAs) with different degrees of substitution, cellulose aminoacetate, and cellulose acetophthalate, and also solutions of model compounds -t~-ghicose and cellobiose.In this connection, we investigated solutions in acetic acid of CAs with various degrees of substitution obtained by the successive saponification of cellulose triacetate at temperatures of 59 and 20°C.The results of the optical rotatory dispersion investigations are given in Table 1, from which it can be seen that CAs with the same qualitative and quantitative compositions of the macromolecules can have negative or positive values of the ORD, depending on the conditions of synthesis. For solutions of CAs obtained at a low saponification temperature -20°C -a transition is observed from the negative to the positive region of optical rotatory dispersion. It can also be seen from Table 1 that the samples containing 54-56% of bound acetic acid obtained at 20°C were dextrorotatory, while those obtained at 59°C were levorotatory.In order to elucidate the factors causing CAs to change from levorotatory to dextrorotatory in the process of saponification, we studied model compounds of one functional composition -glucose and cellobiose -in acetic acid (Table 2). A difference in the optical activities of substances with one functional composition can be explained by a change in the conformational state of the pyranose rings and by rotational isomerism. However, rotational isomeris...

The phenomenon of an increase in the hydrophilic properties of such a polyhydroxy compound as cellulose on a limited substitution of its hydroxy groups by other radicals is due to the existence of a system of strong hydrogen bonds blocking the interaction of cellulose with water but breaking down on partial substitution. However, hydrophilicity is connected not only with the" substitution itself but also with the properties of the substituting radical [1, 2]. It was therefore desirable to study the sorption properties and the thermodynamics of the interaction of mixed cellulose esters with water.We have investigated a water-soluble cellulose acetate (WSCA) with a degree of substitution Fac = 0.72; a watersoluble cellulose acetophthalate (WCAP) with Fac = 0.72, Fph t = 0.08, OH group content 2.2; a water-soluble acetomaleate (WCAM) with Fae = 0.71, Fma I = 0.06, OH group content 2.2, and a water-soluble cellulose aminoacetate (WCAA) with Fae = 0.65, Famin o = 0.51, OH group content 1.84. The degree of polymerization of all the specimens studied was -200.The sorption of water vapor was studied by means of a McBain spiral balance with a sensitivity of -1.3-10 -3 m/kg at 293 K and a residual pressure of 10-3-10 -4 Pa. When the equilibrium values of the amount of water sorbed had been reached, the equilibrium vapor pressure was measured and sorption isotherms were plotted. The heat of mixing was determined in a modernized DAK-I-IA calorimeter. Before the beginning of the experiments, the samples were dried to constant weight and were placed in the working cell of the microcalorimeter. After thermal equilibrium had become established the samples were brought into contact with water vapor. The heat effect was shown on the panel of the integrator and recorded in the form of curves in a diagram. Figure 1 shows isotherms of the sorption of water vapor for all the samples investigated. As has been shown in [3], the sigmoid form of the curves, with a convex initial section, is due to the simultaneous occurrence of two processes: physical adsorption in the pores of the polymer, and its swelling. It follows from Fig. I that mixed cellulose esters have a high sorption capacity in water and that the magnitude of the equilibrium sorption depends on the nature of the substituting radical, decreasing in the sequence WCAM > WCAP > WSCA > WCAA.The sorption isotherms were used to calculate the thermodynamic affinities of water for the mixed cellulose esters. The difference in the chemical potentials of 1 g of water in the phase of a swollen polymer, A/~I, and of pure water, A/~ ~ was calculated by means of the equation