Effect of Crosslinking Density and Dilution during Polymerization on the Stress-Strain and Viscoelastic Behaviour of (2-Hydroxyethyl Methacrylate) Networks in Dry and Swollen States filled with SiO2

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Abstract
Linear viscoelastic and stress-strain behaviour of poly(2-hydroxyethyl methacrylate) PHEMA networks filled with SiO2 and prepared by crosslinking copolymerization has been investigated. The main attention was devoted to the effect of the volume concentration of the filler within the range v f = 0 –0.194, concentration of the crosslinking agent (ethylene dimethacrylate) within the concentration range c = 0.13 – 7.84 %, and water present during polymerization with the volume fraction of water ranging from 0.0 to 0.75. It was established that an increasing concentration of the filler had as its consequence a rapid increase in the modulus in the rubberlike region; this effect is more pronounced than in the case of natural rubber filled with active fillers. The effect of the filler decreases with swelling, which is in accordance with the assumption that the polymer-water interactions are stronger than the polymer-filler interactions. The presence of water during polymerization also leads to a decrease in the effect of SiO2 in both dry and swollen systems. With increasing concentration of the filler, the retardation spectra are shifted toward longer times, and their slopes in the main transition region become smaller; this effect, however, is not pronounced on the whole. Whereas the concentration of the crosslinking agent affects the viscoelastic behaviour most, the water content during polymerization has no effect at all.

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