Patents by Inventor Alice C. Chang

Alice C. Chang has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Copolyimides prepared from ODPA, BTDA and 3,4'-ODA
    Patent number: 5502157
    Abstract: A copolyimide was prepared by reacting 3,4'-oxydianiline (3,4'-ODA) with a dianhydride blend comprising, based on the total amount of the dianhydride blend, about 67 to 80 mole percent of 4,4'-oxydiphthalic anhydride (ODPA) and about 20 to 33 mole percent of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). The copolyimide may be endcapped with up to about 10 mole percent of a monofunctional aromatic anhydride and has unbalanced stoichiometry such that a molar deficit in the dianhydride blend is compensated with twice the molar amount of the monofunctional aromatic anhydride. The copolyimide was used to prepare composites, films and adhesives. The film and adhesive properties were significantly better than those of LaRC.TM.-IA.
    Type: Grant
    Filed: August 31, 1994
    Date of Patent: March 26, 1996
    Assignee: The United States of America as represented by the Administrator of the National Aeronautics and Space Administration
    Inventors: Alice C. Chang, Terry L. St. Clair
  • Solvent resistant copolyimide
    Patent number: 5478916
    Abstract: A solvent resistant copolyimide was prepared by reacting 4,4'-oxydiphthalic anhydride with a diaimine blend comprising, based on the total amount of the diamine blend, about 75 to 90 mole percent of 3,4'-oxydianiline and about 10 to 25 mole percent p-phenylene diamine. The solvent resistant copolyimide had a higher glass transition temperature when cured at 350.degree. , 371.degree. and 400.degree. C. than LaRC.TM.-IA. The composite prepared from the copolyimide had similar mechanical properties to LaRC.TM.-IA. Films prepared from the copolyimide were resistant to immediate breakage when exposed to solvents such as dimethylacetamide and chloroform. The adhesive properties of the copolyimide were maintained even after testing at 23.degree., 150.degree., 177.degree. and 204.degree. C.
    Type: Grant
    Filed: September 1, 1994
    Date of Patent: December 26, 1995
    Assignee: The United States of America as represented by the Administrator of the National Aeronautics and Space Administration
    Inventors: Alice C. Chang, Terry L. St. Clair
  • Direct process for preparing semi-crystalline polyimides
    Patent number: 5464928
    Abstract: The invention is a direct process for preparing semi-crystalline polyimides. This process comprises the steps of: providing a polar aprotic solvent, adding a dianhydride and a diamine to the solvent to form a mixture, stirring the mixture at ambient temperature, and adding glacial acetic acid to the mixture to provide a ratio of polar aprotic solvent to glacial acetic acid which ranges from about 90 to 10 to about 75 to 25 by volume to form a solution. The solution was heated to a range from about 110.degree. C. to about 140.degree. C. to form a polyimide precipitate. The polyimide precipitate was recovered as a semi-crystalline polyimide powder.
    Type: Grant
    Filed: September 1, 1994
    Date of Patent: November 7, 1995
    Assignee: The United States of America as represented by the United States National Aeronautics and Space Administration
    Inventors: Alice C. Chang, Terry L. St. Clair