Studies on swelling, tensile properties and network parameters of HEMA/St copolymeric hydrogels

Five series of hydrogels based on the rigid hydrophobic monomer styrene (St) and the hydrophilic monomer 2-hydroxyethyl methacrylate (HEMA) crosslinked with ethylene dimethacrylate (EDMA) or divinyl benzene (DVB) were synthesized by bulk polymerization. Effects of St content and the type and content of crosslinker on swelling behaviors, tensile properties, effective crosslink density (v_e), molar mass between cross-links (M_C) and polymer-water interaction parameter (χ) of hydrogels were studied. It has been shown that the increase of styrene or crosslinker content in polymerization would lead to changes of swelling behavior, network structure and polymer-water interaction in hydrogels, viz. the decrease of equilibrium water content (w₁) and M_C values, and the increase of volume fraction of polymer in hydrogel (ψ₂), v_e and χ values. These changes represent macroscopically the increase of tensile strength and Young's modulus of the hydrogels. EDMA and DVB have similar crosslinking efficiency in the HEMA70/St30 system.