Homogeneous Poly(acrylamide) Hydrogels Made by Large Size, Flexible Dimethacrylate Cross-Linkers

Homogeneous poly(acrylamide) (PAAm) hydrogels with a relatively high cross-link density was obtained by increasing the distance between the vinyl groups of the cross-linker molecule. The cross-linkers were denoted by DMA-x, where DMA denotes the two methacrylate moieties and x is the number of ethylene glycol units in the molecule, which was varied between 1 and 14. Free-radical cross-linking copolymerization of acrylamide monomer and DMA-x cross-linker was carried in an aqueous solution at 25°C in the presence of ammonium persulfate redox initiator system. Gelation reactions were also carried out in light scattering vials. After a reaction time of 1 day, the scattered light intensities of gels were recorded at various scattering angles. A different behavior was observed if the effective cross-link density Ve was taken as the independent parameter. A clear correlation was found between the size and the efficiency of the cross-linkers and the spatial gel inhomogeneity.