Thermally stable polymers show promise in electrical uses Polyaromatic heterocycles are a new class of high-molecular-weight poly mers with outstanding thermal stabili ties and electrical properties, Japan's Dr. Naoya Yoda told the Fourth Bi ennial Polymer Symposium at the University of Massachusetts. The Toyo Rayon Co. chemist tells C&EN that thermally stable polymers based on amino-carboxylic acids and related compounds have commercial promise. Toyo Rayon is producing de velopment quantities of new types of these high-temperature polymers for electrical uses. As a class, the plastics based on aromatic amino-carboxylic acids and related compounds have properties similar to Du Pont's polyimides. Interest in thermally stable polyaro matic heterocycles has generated a variety of new synthetic approaches to cyclopolycondensations. These con densations produce fully aromatic or pseudo-aromatic polymers, the Har vard-educated chemist and former postdoctoral coworker of Dr. Carl S. Marvel at the University of Arizona (who pioneered the field of high-tem perature aromatic heterocyclic poly mers) explained to the symposium, sponsored by the ACS Division of Polymer Chemistry. Tetrafunctional compounds containing diamino and dicarboxyl groups and their related com pounds are potentially important mon omers for the synthesis of a series of new high-temperature polymers such as polybenzoxazinones, polyquinazolinediones, polyquinazolones, poly (Schiff-base), polyindolones, and polyisoindoloquinazolinediones, Dr. Yoda adds. The cyclopolycondensation reaction variables have been studied in detail by Dr. Yoda and coworkers at Toyo Rayon's basic research laboratories in Kamakura, Japan. The techniques studied include low-temperature solu tion methods, polyphosphoric acid so lution polymerization, and melt poly merization processes. In solution pol ymerizations, an aprotic polar solvent such as N-methyl pyrrolidone is use ful for conducting the polymerization. Water and other competing nucleophiles must be absent if high molecu lar weight is to be obtained, Dr. Yoda adds. Polyaromatic heterocycles of high molecular weight are amorphous, rigid, and tough plastics with high glass transition temperatures. They can be cast into film or spun into fiber. Polybenzoxazinone, for example, is quite stable. The plastic shows a 16% weight loss at 340° C. (at a heating rate of 6° C. per minute); at 450° C. 14 C&EN JULY 8, 1968
thermal degradation begins. At 700° C. there is a 3 3 % weight loss. At 250° C , the life of a polybenzoxazi none film extrapolates to 10 years. The density of the polymer is 1.3 grams per cubic centimeter and it is stable in acids and bases.
Laser used in measuring rates of ultrafast chemical reactions A laser beam is superior to an ultra sonic wave probe for determining the rates of very fast chemical reactions, a team at the University of California's Lawrence Radiation Laboratory in Livermore, Calif., finds. By measur ing the quasi-elastic scattering of laser light by salt solutions, it may be possi ble to analyze reactions that occur within 10~12 second, Dr. Yin Yeh told the 150 delegates who attended the first Debye Memorial Symposium on Laser Scattering at Cornell Univer sity. The ACS Division of Physical Chemistry and the American Physical Society's Division of Chemical Physics cosponsored the conference. The laser technique can be applied to a variety of ultrafast chemical reac tions, such as those involving proton transfer. It should enable biochemists, for example, to gain new insight into the mechanistic detail of enzyme-ini tiated processes, Dr. Yeh points out. He and coworkers Dr. Norris Keeler and Edward J. Britton have studied the quasi-elastic scattering of a laser beam brought about by ionization-deionization shifts that occur in salt solu tions. Even when the solutions are at equilibrium, as far as temperature,
pressure, and concentration are con cerned, they are never entirely free from minute local fluctuations. The return to equilibrium of these spon taneous fluctuations involves a relaxa tion time that's characteristic for the kinetics of the system. Key to the technique that the U.C. physicists devised is the Doppler broadening of laser light's wave length caused by localized fluctuations in the solutions through which the light passes. The degree of wave-length stretch is a measure of the rate of the chemical reaction. Dr. Yeh and Dr. Keeler use a lowpower, continuous-beam, helium-neon laser with a single frequency wave length of 6328 A. They pass the light through the salt solution and into a pressure-scanning Fabrey-Perot inter ferometer that analyzes the Doppler broadening of the beam that emerges from the solution. A chart recording gives a direct reading of the rate at which the ionization-deionization re action takes place in the solution. The "purity" of laser light is such that it's possible to detect a spread of its wave length down to the order of one part in 10 million Α., Dr. Yeh says. Moreover, the laser's spectral line width is essentially independent of all thermodynamic parameters of the reaction system. Also, the laser beam causes no perturbation in the system through which it passes. Working with solutions of zinc sul fate and similar salts, Dr. Yeh and Dr. Keeler have verified reaction data ac quired by ultrasonic probe. They have measured reaction rates down to 10~9 second. They now plan to push this limit back to 10 - 1 2 second.
Lawrence Radiation team and laser apparatus Quasi-elastic scattering
