Dynamic mechanical properties of poly(2‐hydroxyethyl methacrylate) hydrogels

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Abstract
Homogeneous and heterogeneous poly(2‐hydroxyethyl methacrylate) hydrogels were prepared by copolymerization of 2‐hydroxyethyl methacrylate and small amounts of ethylene glycol dimethacrylate in the presence of water; concentrations of water (V1) in the polymerization mixture and the volume fractions of water (v1) of the gels swollen to equilibrium were 40, 50, 60, 70% by volume, and 0.475, 0.541, 0.669, 0.778, respectively. From the homogeneous (clear) hydrogel (V1 = 40%) preparation, four hydrogels were prepared with v1 = 0.434, 0.418, 0.378, 0.326. Tensile dynamic moduli were measured in the frequency range from 0.006 to 0.6 cps and the temperature range from 0 to 40°C. In these cases, the influence of swelling on the shape of the relaxation spectra and on the monomeric unit friction coefficient was studied. The dependence of the friction coefficient on water concentration was interpreted in terms of free volume. In the heterogeneous (opaque) gel preparations (V1 = 50, 60, 70%), the effect of the aqueous phase in the system on the mechanical behavior was described by a modification of the blending law of Ninomiya. For the systems with V1 = 60% and 70% the shapes of the storage and loss moduli in the main transition region and the friction coefficient were similar to those of the homogeneous gel with V1 = 40%, except for the decrease in absolute value of the storage moduli. For the system with V1 = 50% the shape of the relaxation spectrum changes appreciably and the wedge distribution does not hold.

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