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The solubility parameters of pure poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(2-hydroxyethyl methacrylate/itaconic acid) [P(HEMA/IA)] hydrogels were determined by 20 solvents with various solubility parameters in swelling experiments. The solubility parameter of pure PHEMA was 26.93 Ϯ 0.46 (MPa) 1/2 . The effect of mole percentages of itaconic acid (IA) in P(HEMA/IA) hydrogels on the solubility parameter was investigated. The measured values were compared to literature and solubility values theoretically determined by group contribution values of van Krevelen and Hoy. The incorporation of IA into the hydrogel system slightly increased the solubility parameter.

Hydrogels with various ionic group contents were prepared from acrylamide and crotonic acid (CrA) monomers with 0 -12.9 mol % CrA in aqueous solutions by radiation-induced polymerization and gelation with ␥ rays from a 60 Co source. The volume swelling ratio of the poly(acrylamide/crotonic acid) hydrogels was investigated as a function of the pH and ionic strength of the swelling medium and the type of counterion in the swelling medium. The volume swelling ratio increased with an increase in pH and a decrease in the ionic strength. The volume swelling ratio of these hydrogels was evaluated with an equation, based on the Flory-Huggins thermodynamic theory, the James-Guth phantom network theory, and the Donnan theory of swelling of weakly charged ionic gels, that was modified here for the determination of the molecular weight between crosslinks (M c ) and the polymer-solvent interaction parameter (). The modified equation described very well the swelling behavior of the charged polymeric network. The same equation also provided the simultaneous measurement of these parameters for the systems investigated.

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The thermal behavior of poly(2-hydroxyethyl methacrylate) [PHEMA] homopolymer and poly(2-hydroxyethyl methacrylate-co-itaconic acid) [P(HEMA/IA)] copolymeric networks synthesized using a radiationinduced polymerization technique was investigated by differential scanning calorimetry, thermogravimetric analysis, and Fourier transform infrared spectroscopy. The glasstransition temperature (T g ) of the PHEMA homopolymer was found to be 878C. On the other hand, the T g of the P(HEMA/IA) networks increased from 888C to 1178C with an increasing amount of IA in the network system. The thermal degradation reaction mechanism of the P(HEMA/ IA) networks was determined to be different from the PHEMA homopolymer, as confirmed by thermogravimetric analysis. It was observed that the initial thermal degradation temperature of these copolymeric networks increased from 2718C to 3008C with IA content.