Effect of various crosslinkers on properties of 2-hydroxyethyl methacrylate/E-51-demethacrylate polymeric hydrogels

Five series of polymeric hydrogels based on 2-hydroxyethyl methacrylate (HEMA) of 90 wt% and a macromolecular crosslinker - E-51 dimethacrylate (E-51-DMA) of 10 wt% were prepared by bulk copolymerization, crosslinked with N, N′-methylene-bisacrylamide (MBA), divinyl benzene (DVB), ethylene dimethacrylate (EDMA), 1, 1, 1-triacryloxymethyl propane (TAP) and 2, 2, 2-triacryloxymethyl ethanol (TAE), respectively. The effect of the species and content of crosslinkers on swelling properties, Young's modulus, effective crosslinking density (v_e) and polymer-water interaction parameter (χ) were studied, and crosslinking efficiencies of various crosslinkers were also compared. As the amounts of crosslinkers increased, a large number of crosslinks will be generated within hydrogels, so the equilibrium water content (EWC) decreased, in contrast, the volume fraction of polymer in hydrogels (φ₂) increased. As a result, the enhancement of effective crosslink density (v_e) concerning network structures and interaction parameter (χ) that represents thermodynamic interaction between water and polymers could be observed. The crosslinking efficiencies of five adoptive crosslinkers in E-51-DMA10/HEMA90 hydrogel systems were fitted from the relationships between effective crosslink density and theoretical crosslink density, and their order was as follows DVB > EDMA > TAE > MBA ≈ TAP. The changing magnitudes for these above-mentioned parameters may be attributed to the nature of crosslinkers and their crosslinking efficiencies.