Non-hydrolyzable, hydrophilic, heterocyclic cross-linking agents for cross-linking vinyl comonomers are provided. The cross-linked copolymers form optically transparent, high water content, and high refractive index hydrogels having long-term stability which are useful as intraocular lenses and superabsorbents. The cross-linkers are selected from 4,6-divinylpyrimidine, 2,5-divinylpyrazine, 1,4-divinylimidazole and 1,5-divinylimidazole.
WATER MISCIBLE NON-HYDROLYZABLE CROSS-LINKERS AND HIGH REFRACTIVE INDEX HYDROGELS PREPARED THEREWITH