Conductive polymers get closer to home.

Conductive polymers get closer to home

Easy-to-process polymers that conduct electricity are edging closer to largescale commercialization. Researchers envision many novel uses, including antistatic coatings for delicate electronic equipment, lightning protection for airplanes, spark-resistant clothing for people working near explosive fumes, and shilds to block electromagnetic radiation emitted from computers and TVs.

For years, processing and stability problems have limited conductive polymers to small-scale specialty applications. Two scientists now say they have modified a conducting polymer so that it appears free of such problems. "We have a very simple process here in a very simple polymer," says physicist Arthur J. Epstein of Ohio State University in Columbus, who did the work with chemistry graduate student Jiang Yue. Their report appears in the March 28 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY.

Polyaniline -- a molecular chain in which benzene rings alternate with nitrogen-centered amine groups -- serves as the starting material for the new conducting polymer. Epstein and Yue first convert this backbone into an insulating from and then chemically bond acidic sulfonate groups to half of its benzene rings. In a process known as doping, the sulfonate groups enhance polyalinine's conductivity by contributing negative charge to nearby nitrogen atoms, freeing other electrons in the molecule to travel down the chain. By processing the polymer so that millions of chains line up side by side, the Ohio team and others can make materials in which conduction electrons can almost always avoid dead-ends by hopping to adjacent chains. Epstein says the sulfonated polyaniline maintains its conductivity even when dissolved in water.

Other polymer researchers are taking different paths toward the same destination. Materials scientist Paul Smith of the University of California, Santa Barbara, says he prefers to dope the polyaniline by allowing chloride or other ions to diffuse into the polymer rather than going through the chemical step of bonding dopant molecules or atoms directly to polymer molecules. Epstein contends this "external" type of doping poses problems that his "self-doping" tactic circumvents. For instance, he says, external dopants can leach out of polymers exposed to heat or moisture. He and Smith concur, however, that their contrasting tactics provide healthy competition for hastening discoveries.

In either case, it will take industrial commitment to turn the gram-scale quantities made in basic research labs like Epstein's and Smith's into the kilogram quantities, needed for larger-scale commercialization. Hexcel Corp., a hightech materials company based in Dublin, Calif., took a step in that direction on Feb. 28 when it announced its intention to develop methods for the first large-scale production of polyaniline. A spokesman for Hexcel says the company already has produced batches in the several-kilogram range.