Achieving Greater Precision in New Polymer Materials

Originally Published MDDI January 2002

R&D DIGEST

Achieving Greater Precision in New Polymer Materials

A team of scientists at the University of Massachusetts (UMass; Amherst, MA) are reconsidering conventional thinking about how polymers harden, in hopes of developing finer control over the flexibility of specialty plastics.

According to Murugappan Muthukumar, PhD, UMass researcher, when plastics are manufactured, the material is heated and then cooled so that it will harden, or crystallize. The researchers have been examining the way in which the polymers crystallize and have found that they essentially "fold back and forth in tight layers, producing a wide and very thin crystal, perhaps just 10 nm thick—about 10,000 times thinner than a human hair."

The conventional theory suggests that polymers of any length would eventually crystallize entirely if given enough time. Because polymers can be very long, however, the theory could not be tested in a laboratory; it theoretically would have taken an infinite length of time for the longest polymers to crystallize. Says Muthukumar, "Whether polymers of this size would ever completely crystallize has been a puzzle for 60 years."

Computer simulations of polyethylene crystallizing were conducted by the team to test the theory. The researchers found that when very lengthy polymers harden, they never actually achieve total crystallinity. The polymers were found to reach a state of equilibrium before all of the necessary folding and assembling of the crystal is completed. "We have shown that finite crystallinity is actually the equilibrium state," says Muthukumar.

He adds, "How to control crystallinity is a big issue in industry. If a material is too crystalline, it may be too brittle for its intended use. Our findings give a potential way of controlling flexibility."

The researchers believe that their findings could promote a better understanding of certain aspects of what is called "the protein-folding problem." They explain that proteins are biological polymers. In order for a cell to function properly, a cell's proteins must fold themselves precisely into very complex configurations. Scientists are trying to learn how proteins manage to fold themselves with such precision.

Says Muthukumar, "The way the amino acids interact has an effect on how they fold, and the way in which the individual amino acids are connected tweaks the final shape of the protein. Scientists want to know what the effect of chain connectivity is in protein folding before addressing the chemical subtleties. Polyethylene crystallization is the simplest protein-folding problem."

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