Hydrogels and methods for their production

Abstract

Forming graft copolymers in water using labeling of water soluble polymers with photoinitiators. The water soluble polymers can form environmentally responsive hydrophobically stimulated cages, which respond to pH, salt concentration, and/or the addition of water miscible solvents to the aqueous solutions. When the cage is “closed,” irradiation leads to radicals that cannot escape from the cage and therefore don't cause substantial polymerization of water soluble monomers in the same solution. When the cage is open via change of pH, salt concentration and/or solvent composition, the photochemically produced free radicals become exposed and cause polymerization. Under certain conditions, only graft copolymers will be formed. These graft copolymers can form a physical hydrogel in which the crosslinks are reversible. Consequently, the gel and sol states are likewise reversible. These hydrogels and graft copolymers may also be formed by a variation of the invention in which the photoinitiator groups are covalently linked to water soluble polymers that do not form cages. In this case, water soluble monomers capable of free radical polymerization in the aqueous solution form grafts to the water soluble polymer allowing formation of physical hydrogels. The physical hydrogels formed in either case show properties responsive to pH, salt and/or solvent composition, so that the hydrogels may be rendered to a powder by addition of methanol or other non-solvents and these powders can reform the gels.

Dependencies are inferred from the claim text.