Chemistry.

In the past, glue has proved the weak link in steel structures bonded by adhesives. But when scientists use a new class of polymers to prime the steel first, bonding improves by up to 50 percent, says Morton H. Litt, a polymer chemist at Case Western Reserve University in Cleveland.

He and Case Western Reserve colleague Toshio Kadowaki made these polymers from two kinds of starting units, or monomers. They used two to 22 monomers of one and 10 of another. The Cleveland researchers modified the first monomers by adding two hydrogen and oxygen side groups -- called hydroxyl groups -- to the ends of the units' side chains. When the researchers coat steel with this polymer, hydroxyl groups bind strongly to the iron in the oxide layer that covers the steel surface. The parts of the polymer that stick up, away from the steel, then link tightly with adhesive coats placed over the primer, Litt explains.

The polymer comes with a high price tag, but it takes a layer just one molecule or so thick to prime a surface. The polymer would also make paint stick better, he adds.

Litt helped develope this class of polymers almost 30 years ago. The backbones of the final polymers consist of carbon atoms, but a nitrogen occurs every third position. That makes them different from--and more versatile than--most polymers, Litt says. "I think this particular class of polymers will eventually find many uses."

New odorless disinfectant 

It's hard to imagine a swimming pool without that acrid chlorine odor. But a new disinfectant developed to protect eggs against bacteria may one day keep pools odor-free as well as microbe-free. S. Davis Worley, an organic chemist at Auburn (Ala.) University, has been developing N-halamine compounds since 1980. He and his colleagues now have six new ones that not only kill bacteria and algae, but also are nontoxic, inexpensive and do not break down in water or corrode containers, Worley says.

Typically, poultry processors clean eggs by washing them in water and chlorine. The chlorine kills bacteria on the shells, but it also escapes into the air, requiring technicians to keep adding more, he says.

N-halamines also contain chlorine. They consist of five-member rings that include one or two nitrogen atoms. But the nitrogen locks chlorine to the molecule, so it cannot escape. Thus the compound remains active for long periods, Worley explains.

He envisions spraying these disinfectants onto eggs to kill bacteria on the shells or, for longer-lasting protection against infection, coating them with a mixture of mineral oil and N-halamine. In addition, he thinks these compounds will prove cost-effective and useful as swimming pool and household disinfectants.

A new way to build a better polymer

The aerospace and electronics industries depend on polyimides because these polymers possess exceptional strength and remain stable at high temperatures. However, chemists find polyimides difficult to process.

"What makes them very desirable is also the same thing that gets you into trouble," says Laren M. Tolbert of the Georgia Institute of Technology in Atlanta. To get around this shortcoming, Tolbert and his colleague Zhanqi He have developed versatile new starting materials for making polyimides.

Polyimides consist of rings of atoms linked in series. Instead of making their polyimide from compounds that already contain these rings, Tolbert and He start with precursors that form the rings as they come together. "We're creating the ring as part of the cross-linking," Tolbert explains.

Previously, materials scientists tended to use polyimides primarily for high-strength fibers, finding that these insoluble polymers work less well as coatings. However, researchers may now have an easier time using polyimides as coatings. They can spread a surface with the new precursors, then cause the polyimide to form in place by heating the material, Tolbert says. So far, the new polyimides withstand high temperatures as well as those made the traditional way, he adds.

Color chemistry in a bottle

Almost anyone can make a red rose white, then red again, by exposing it to a few common chemicals. In the past, teachers performed this magic by bleaching flowers with sulfur dioxide gas from a cylinder. But the need for a cyliner and the possibility that gas might escape into the classroom caused many to shy away from this experiment, says Dawn Hygaard, a chemistry student at Moorhead (Minn.) State University. So when asked to give a chemistry lecture to her son's fourthgrade class, she decided to revise the procedure. "We made it safer by making the gas within a reaction vessel," Nygaard says.

She and a professor, Dennis Mathiason, placed sodium sulfite in a quart jar with vinegar, suspended a rose inside, then sealed the jar and put it in warm water for 15 minutes. The sodium sulfite and vinegar react to form the decolorizing gas, and the rose grows pale after about five minutes, says Nygaard. She can bring back the color by dipping the rose in phosphoric acid or hydrochloric acid.

"The experiment has been set up so we can do it classes where they don't have [special] chemicals and where safety is more of an issue," says Mathiason.

The experiment works because some flower pigments change color as the acidity of their surroundings changes. Nygaard also made purple irises and orange gladioli turn white. But while blue bachelor's buttons also turned white in the jar, they became dark pink, not blue, when she dipped them in acid.

Antimosquito fragrances

One day the human nose may be unable to tell as insect repellent from a perfume. A survey of 2,000 compounds commonly used as scents or flavors reveals that several dozen appear as unappealing to mosquitoes and houseflies as they are appealing to people. "For the first time, we showed that fragrance chemicals, which everybody is using, could be used to control things like houseflies and mosquitoes," says Braja D. Mookhergee, a natural products chemist at International Flavors & Fragrances, Inc., in Union Beach, N.J.

The researchers assessed the insects' preferences using a device called an olfactometer, built by Jerry F. Butler, an entomologist at the University of Florida in Gainesville. For the tests, Butler places about 100 insects in the device's central chamber. The chamber contains 10 or so openings, each with a different compound. The device then electronically measures how often the insects visit each opening. The insects avoided jasmonate, which occurs naturally in tea and several flower oils. Nor did they like the chemicals beta and alpha damascone, even though other compounds with a similar rose-apple odor attract insects, Mookhergee reports.

One needs much higher concentrations of these compounds than commonly found in foods and cosmetic products to make them effective repellents, says Mookhergee. But many of these substances are still pleasing to smell, even at high concentrations, he adds. During the next two years, his company plans to develop mixtures of these compounds for possible use in air freshener sprays or odor strips that double as fly and mosquito deterrents.