THE STRUCTURE OF CROSS-LINKED POLY(GLYCERYL METHACRYLATE) HYDROGEL NETWORKS

Poly(glyceryl methacrylate) hydrogels with different degrees of hydration (75-98% H) and cross-linking densities (X = 0.005-0.05 mol tetraethylene glycol dimethacrylate/mol glyceryl methacrylate) have been prepared by solution polymerization. Cross-linking densities of the fully swollen hydrogels were analyzed using a modified Flory equation. Poly (glyceryl methacrylate) gels polymerized with no added cross-linker were found to be highly cross-linked, the degree of cross-linking depending upon monomer dilution at polymerization. Modeling studies indicated that entanglement of polymer chains explained the highly cross-linked nature of these materials. Gels polymerized with tetraethylene glycol dimethacrylate exhibited higher cross-link densities than did gels polymerized with no added cross-linker. However, for gels polymerized with cross-linker, but at different initial dilutions, cross-linking densities varied depending upon initial concentration, indicating that entanglement contributed appreciably to cross-linking. These hydrogels may be regarded as highly swollen entangled networks, contrary to previous views. Correlation of these findings with those from earlier studies on the ultrafiltration behavior of the poly (glyceryl methacrylate) hydrogels suggested that the packing density of polymer fibers in the matrix may be more predictive of ultrafiltration behavior than is mesh size.