Finally, the gel fractions of samples crosslinked at 120 -200 °C were determined after extensive extraction of the sol fraction (Figure ). All samples showed a decrease of sol fraction with an increase of crosslinking temperature leveling off at 12 % for samples obtained at 200 °C with 20 wt. % polyperoxide. At lower crosslinking temperature, significantly higher sol fractions were determined. Interestingly, samples crosslinked with P[PM-co-BA-co-MA] at 160 °C show a somewhat higher sol fraction for 20 wt.% crosslinker compared to 15 wt.% (Figure , green vs. black columns). Hydrogels obtained at 120 °C and 20 wt. % of P[PM-co-MA] show higher sol fractions than the samples prepared with P[PM-co-BA-co-MA]. For 15 wt.%, the situation was reversed. At this point, we cannot explain these trends. In most cases, heating time does not have significant influence on the sol fraction. Only at 120 °C, gel fraction increases notably with incubation time. To investigate the viscoelastic properties of hydrogels, rheological measurements of the hydrated samples were performed (Figure ). Since samples crosslinked at 120 °C were too weak to handle properly, only hydrogels crosslinked at 160 -200 °C and crosslinker concentrations of 15 and 20 wt. % were studied. As G'˃˃G" for all samples and all measurement parameters, all samples can be characterized as hydrogels . The G' and G" values were relatively independent of the frequency behavior with deviations only becoming apparent at or above 100 rad/s. As can be expected, an increase in crosslinker concentration and temperature (and therefore degree of crosslinking) resulted in an increase of G'. Chemical composition of the polyperoxide does not have significant influence on the viscoelastic properties of the obtained hydrogels (Figure ). The visual appearance of a sample obtained after 40 min incubation at 160 °C shows a rough surface and air bubbles inside the investigated samples (Figure ). Such a highly porous and irregular structure was typical for all investigated hydrogels. It must be noted that such heterogeneities may have a significant influence on the rheological measurements. Therefore, that the numerical values should be considered with great care.