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.

Sorption isotherms and heats of immersion of water in poly(2-hydroxyethyl methacrylate) (PHEMA) and in poly[2-(2-hydroxyethoxy)ethyl methacrylate] (PHEOEMA) were determined at 25 "C and the Gibbs energy, enthalpy and entropy of mixing were calculated from the data.The results confirm that the physical state of the polymer plays a decisive role in the thermodynamics of sorption. At the temperature of measurement, pure PHEMA is in the glassy state and after sorption of a certain amount of water it passes into the viscoelastic state. Similar to other cases of mixing of a glassy polymer with a low-molecular weight liquid, the entropy and enthalpy changes are negative, with contributions due to the difference between the physical states of both pure components predominating in them. The thermodynamics of liquid mixtures can be used only for PHEOEMA which at 25 "C is in the viscoelastic state. The mixing of water (especially of the first additions) with PHEOEMA is exothermal, being at the same time connected with a negative residual entropy, the effect of which predominates at 25 OC. As a result, the affinity of water to the polymer, expressed through a change in the Gibbs energy, is comparatively weak. This is why in this system no strongly bound water is involved, even if the A H and AS values indicate some sort of increase in ordering during mixing. a) Part 1 : cf. l).