Network parameters study of novel P(HEMA-co-NEVER) copolymeric hydrogels

A series of hydrogels based on macromonomer novolac epoxy vinyl ester resin (NEVER) and hydrophilic-2-hydroxyethyl methacrylate (HEMA) were synthesized by bulk copolymerization. The effects of NEVER content and temperature on network parameters such as effective crosslink density (v_e), molar mass between crosslinks (M_c) and polymer-water interaction parameter (x) of hydrogels were studied on the basis of swelling and tensile properties. The increase of NEVER content can enhance hydrophobic bonding within hydrogel, leading to the decrease in equilibrium water content (EWC) and the increase in volume fraction of polymer in hydrogel (Φ₂) and tensile strength, Young's modulus, v_e and x values of hydrogels also increases and M_c decreases. When the temperature is increased from 273 K to 343 K, the hydrogel H/N7 undergoes decreasing in EWC and increasing in Φ₂ and X values. The thermodynamic analysis indicated that the swelling process is an exothermic process.