Sung Keun Yang

US Patent:

6559223, May 6, 2003

Filed:

Feb 22, 2001

Appl. No.:

09/790739

Inventors:

Mark M. Green - New York NY
Sung Yun Yang - Cambridge MA

Assignee:

Polytechnic University - Brooklyn NY

International Classification:

B01J 1300

US Classification:

524831, 516 99, 522 9, 522 33, 522175, 522183, 522904, 522905, 524916, 5253294, 525936

Abstract:

Forming graft copolymers in water using labeling of water soluble polymers with photoinitiators. Water soluble polymers can form environmentally responsive hydrophobically stimulated cages. The cages, which contain initiating radicals after irradiation, may be âopenedâ or âclosedâ by changes in environmental conditions. When the cage is closed, the radicals are trapped inside and thus do not cause substantial polymerization of water soluble monomers in the same solution. When the cage is closed, the radicals escape and cause polymerization. In another variation, hydrogels and graft copolymers are formed by covalently linking phototoinitiator groups to water soluble polymers that do not form cages. Thus, monomers may form grafts to the 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 non-solvents and these powders can reform the gels.

US Patent:

20020161107, Oct 31, 2002

Filed:

Feb 22, 2001

Appl. No.:

09/790740

Inventors:

Mark Green - New York NY, US
Sung Yang - Cambridge MA, US

Assignee:

Polytechnic University

International Classification:

C08K003/00

US Classification:

524/802000, 522/003000

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.