Effect of crosslinkers on photocopolymerization ofN-vinylpyrrolidone and methacrylates to give hydrogels

N-Vinylpyrrolidone (NVP) and methacrylates are frequently copolymerized to give hydrogels useful as contact lenses. However, the nature of their copolymerization was not well understood. In this study, the effect of a crosslinker on the photocopolymerization of NVP and 2-hydroxyethyl methacrylate (HEMA) was discussed. It was found that crosslinkers with a vinyl carbonate group can copolymerize with NVP better than those containing an allyl group, which, in turn, are better than those containing a methacrylate group. A crosslinker with a vinyl carbonate and a methacrylate group can copolymerize NVP and HEMA the best in terms of giving hydrogels with the highest water content, followed by a crosslinker with a combination of allyl and methacrylate groups. Crosslinkers with only methacrylate or vinyl carbonate groups gave hydrogels either too fragile or too stiff to be useful.