Stanford News

2/17/97

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Elastic plastic moving from lab to industry

Robert Waymouth never dreamed that his chemistry experiments might point the way to a better, cheaper disposable diaper.

Waymouth, associate professor of chemistry, will describe that unanticipated commercial utility of his research on Feb. 17 at an American Association for the Advancement of Science symposium titled "Basic research: So what have you done for us lately?"

What Waymouth calls "off-the-wall" experiments led him and graduate student Geoffrey Coates to develop a process in which they can make polypropylene ­ ordinarily a stiff plastic ­ that can flex like a rubber band. In fact, the team's method permits them to make the polymer in a variety of forms ­ super-springy, somewhat stretchy or stiff as a board.

His experiment demonstrates that an investigator's small investment of time in a creative experiment sometimes can develop into something much larger ­ in his case, a commercial venture with Amoco Corp., Waymouth says.

Amoco, the exclusive worldwide licensee of his discovery, wants to use his stretchy polypropylene for a variety of products, ranging from those diapers to automotive dashboards. Officials at Amoco estimate that U.S. sales of rubbery polypropylene could reach $150 million five years after commercialization. The value of products made from the polymer could top $600 million per year.

"We weren't trying to make an elastic polymer ­ if we had been, we might have taken a much more conservative approach," Waymouth said.

A potential danger of doing purely product-oriented research is missing out on fundamental scientific discoveries, he said. "If you focus too narrowly on an application, you lose sight of how peculiar Mother Nature really is."

As Waymouth tells the tale, the finding was serendipitous. Coates performed the critical experiment that resulted in their discovery while working on another project for his thesis research. "Soon after," Waymouth said, "we realized that this discovery was more important than what we were trying to do."

That accidental discovery, which Stanford patented, has economic and environmental impact. In commercial production, rubbery polypropylene should cost one-third to one-quarter less to produce than other pliable plastics, Waymouth said.

Unlike rubber and most plastics, polypropylene can be melted and recycled. Using elastic polypropylene for automotive interiors such as dashboards and upholstery could make it easier to recycle nearly 100 percent of an automobile, he said.

The properties of ordinary hard polypropylene already make it big business. Thirteen billion pounds are sold each year, and it's everywhere ­ from toys to Tupperware to recycling bins.

Both industry and the government are supporting the commercialization of Waymouth's elastic plastic. Amoco has a $10 million grant from the National Institute of Standards and Technology of the Department of Commerce to expand the use of polypropylene.

But rubbery polypropylene also has piqued the interest of the scientific community. To make the stretchy polypropylene, Waymouth and Coates designed what they call an "oscillating catalyst," a novel strategy for making polymers.

"It's truly a cutting-edge approach to very difficult chemistry," said Roman Salij, development manager at Amoco Chemicals.

Catalysts ­ molecules that makes it easier for a chemical reaction to occur ­ ordinarily permit only one type of reaction, leading to a single type of product.

Waymouth and Coates' catalyst is fundamentally different: The molecule oscillates ­ actually changing shape during the reaction.

That capability can affect polypropylene, which is a polymer ­ a long chain molecule synthesized from a large number of identical chemical units, called monomers. Depending on its shape, the oscillating catalyst changes the way the monomers are hooked together in the growing polymer chain. "How you put the link in the chain determines whether the polypropylene is stiff or stretchy," Waymouth explained.

Waymouth likens the process to making pasta with a machine. "If you want to make linguini, you use an attachment that extrudes linguini. To make spaghetti, you use the spaghetti attachment. Now imagine that you could change the shape of the attachment as you extruded the pasta. You'd get segments of spaghetti, linguini, spaghetti, linguini, connected together in a chain. Our catalyst works something like that."

By changing the temperature and pressure of the reaction, which Waymouth says is easy to do, he can fine-tune the degree of elasticity, he added.

Using an oscillating catalyst also streamlines polymer synthesis, said John Brauman, professor of chemistry and department chairman. "Anything you can do in one pot on a continuous basis is much better."

While the list of possible uses for elastic polypropylene is long, it won't replace rubber, Waymouth emphasized. Anything that must tolerate very high temperatures ­ like tires ­ can't be made from a substance that melts.

This article was written by News Service intern Alison Davis.

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By Alison Davis