Abstract:The specific isobaric heat capacities of poly (methylmethacrylates) (PMMA) having various tacticities were measured by the DSC method within a broad range of temperatures including the glass transition. Glasses with uniform thermal history were used in the measurements and the data were treated by employing a procedure which provided the "thermodynamic" Tg independent of the experimental conditions. The semiquantitative validity of Boyer's empirical relation Tg• Ac~ = const, was confirmed; also it was found that within the limits of experimental accuracy the cp, g values at 298 K and c~,z values at 400 K are independent of the tacticity of the sample.Using the data thus measured and linearized equations representing the dependence of Tg on the content of iso-, syndio-and heterotriads, the Tg values of pure isotactic PMMA and pure syndiotactic PMMA were found to be respectively 315 K and 397 K.

An equation derived from the Flory-Huggins relation with the concentration-dependent interaction parameters gij and the ternary parameter gT was used in the correlation of reported data on the preferential sorption in macromolecular coils. A linear plot was suggested, assuming that the dependence of gT on the composition of the mixed solvent resembles that of g,,, i. e. gT(ul) = ugglz(ul). Linear correlation could be carried out in 19 ternary systems out of 22, and the correlation constants were used to calculate the difference of interaction parameters g,, -(V, / V2) gz3 and the proportionality constant ug. For most systems, ug is positive and smaller than unity; for systems containing chloroform it approaches zero. The difference between the interaction parameters gij and the interaction parameters xij is discussed.A comparison between the difference g,, -(V, / V,) g,, obtained by a linear correlation of data on preferential sorption with the values calculated using data on the respective binary systems was possible only for the system benzene/cyclohexane/polystyrene; the fit was very good. It is shown how the individual parameters of the Flory-Huggins equation affect the occurrence, position and type of inversion in preferential sorption. 0025-1 16X/82/12 301 9-22/$03.O0

The heat capacities of water swollen poly[2-(2-hydroxyethoxy)ethyl methacrylate] were determined in a DSC-2 calorimeter within the temperature range 220-350K for concentrations from 0 to 1,2g of water per 1 g of the polymer. At temperatures above 0°C the partial specific heat capacity of water in gel is concentration independent and equal to the specific heat capacity of pure liquid water.It seems, therefore, that water does not form stable icelike structures near polymer chains. To analyze phase transformations of water in gel below O"C, general thermodynamic equations were derived and used as a basis for suggesting criteria which allow to decide whether in a given experiment the phase transformation proceeded in an equilibrium way. In measurements below the melting point of ice the conditions for an equilibrium process consist in the preceding heating of the frozen sample to a temperature close to the melting point, followed by cooling to 220K. The assessed composition dependence of the melting point depression is consistent with the dependence of activity on concentration obtained from measurements of water vapour sorption at 35°C. Analysis of data on the heat capacity below 0°C led to the conclusion that at a water content of 0,4g/g and lower, or at temperatures below 250 K the crystallization of water from gel was inhibited by kinetic factors originating probably in the reduced diffusivity of water in gel, due to the reduced, mobility of polymer chains. Hence, non-freezing water need not be identical with "strongly bound" water; in the study of water structure in polymers based on heat capacities, preference should be given to data obtained at usual and elevated temperatures.

No abstract

An equation for the total sorption potential Y derived from the modified Flory-Huggins equation and containing concentration-dependent interaction parameters, including the ternary parameter ,yT, was used to correlate reported data on intrinsic viscosities in mixed solvents. Similarly to the evaluation of data on preferential sorption, the assumption of proportionality between the ternary parameter and the interaction parameter of components of the mixed solvent, g,, , was successfully applied to the case of total sorption. The assumption proved to be useful in the treatment of 12 ternary systems, if the single-liquid approximation was employed. The calculated proportionality constant between the ternary parameter and g,, has properties similar to that evaluated from the data on preferential sorption. The conditions of occurrence of a maximum or minimum in the dependence of total sorption on composition are discussed.