List of high-temperature polymers grows ^CHICAGO
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compounds to the growing list of high-temperature polymers. In research at Wright State University, Dayton, Ohio, Charles E. Browning has synthesized three new polyimides which are stable to 500° to 600° C. Dr. H. Wayne Hill, Jr., and James T. Edmonds, Jr., of Phillips Petroleum Co., Bartlesville, Okla., have come up with a new process producing arylene sulfide polymers, compounds stable to about 500° C. and serviceable to about 300° C. Details of both were presented to the Division of Organic Coatings and Plastics Chemistry. Polyimides, prepared by reacting dianhydrides with diamines, typically have good resistance to thermal and oxidative degradation. They are used in protective coatings and films and, more recently, have found application in high-temperature structural composites and adhesives. Because of their good mechanical properties, they are particularly useful as structural materials. Starting material for the new polyimides synthesized by Mr. Browning was a new monomer: 2,3, 6, 7 - anthraquinonetetracarboxylic dianhydride ( ATCD A ). Other monomers were 2,6-diaminoanthraquinone (DAA), ??i-phenylenediamine (m-PDA), and 1,8,4,5-naphthalenetetracarboxylic dianhydride (NTDA). Three polymers. Three polyimides were synthesized by reacting ATCDA with DAA, ATCDA with m-PDA, and NTDA with DAA. Then Mr. Browning determined the properties of these compounds and how they undergo thermal and oxidative degradation. Thermogravimetric analyses in air and helium show, he said at a symposium on new high-temperature polymer systems, that these polyimides (which are powders) don't lose any significant weight below 450° C. in air or 550° C. in helium. To study the mechanism of degradation, he then made films of the polyimides—with the exception of the one obtained from reacting NTDA with DAA. A film of that polymer couldn't be prepared because only lowmolecular-weight polyimide powders were obtained from the various reactions tried, he explains. Films of the two polyimides were strong. However, the film of the polyimide produced from ATCDA and DAA was brittle, while the other film was flexible. The brittle film showed a weight retention of 35% after 30 hours at 400° C. in oxygen. Two polyimides gave the same gas-
eous degradation products: carbon dioxide, carbon monoxide, and hydrogen cyanide. The investigation suggests that oxidative attack takes place preferentially at the electron-rich amine-benzenoid portion of the polymers. As for thermal degradation, two mechanisms probably occur, one involving the cleavage of C-C and C-N bonds to give char and carbon monoxide, the other involving the decomposition of the imide to a nitrilebearing species with simultaneous evolution of carbon dioxide. The nitrile would be the hydrogen cyanide source, Mr. Browning says. Polyphenylene sulfide. Until the development of the new process by Phillips Petroleum to make arylene sulfide polymers, these compounds were essentially lab curiosities. The problem was technical difficulties in manufacturing them. Phillips is now offering these polymers, polyphenylene sulfides, in development amounts. Polyphenylene sulfide is a crystalline polymer with a symmetrical, rigid backbone chain consisting of para-
substituted benzene rings connected by a single sulfur atom between the rings, Dr. Hill said at the symposium. The polymer melts at 288° C. (550° F ) , resists attack from a variety of chemicals, and is nonflammable. There are no known organic solvents for the polymer below about 200° C. and thermogravimetric analysis in helium or air indicates no appreciable weight loss below 500° C. In addition, the polymer has good retention of mechanical properties at high temperatures. Coatings formulated from the polymer can be applied on metal surfaces at room temperature or up to about 400° C. Currently they are being evaluated for corrosion resistance on valves, pumps, pipes, tanks, and other industrial equipment used in chemical plants and oil refineries. The polymer also can be injection molded to hard, strong, stiff objects that retain their mechanical properties to 300° C , Dr. Hill points out. Potential applications include mechanical seals for pumps, piston rings, and other equipment.
H. Wayne Hill, Jr. (left), and James Edmonds, Jr., examine new polymer applications SEPT. 28, 1970 C & E N
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