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December 10, 2001
Volume 79, Number 50
CENEAR 79 50 pp. 45-55
ISSN 0009-2347
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[Previous Story] [Next Story]CHEMISTRY HIGHLIGHTS 2001

POLYMER CHEMISTRY. In polymer chemistry research, advances announced this year included shape-memory and self-healing polymers and doubly activated metallocene catalysts.

Novel shape-memory polymers were made to order this year by biomaterials department head Andreas Lendlein and graduate student Annette M. Schmidt at the German Wool Research Institute, Aachen, and professor of chemical engineering Robert Langer of MIT [Proc. Natl. Acad. Sci. USA, 98, 842 (2001); C&EN, Feb. 5, page 5]. Other shape-memory materials--such as nickel-titanium alloys used in orthodontic wires and eyeglass frames--had already been available. But shape-programming of metal alloys is a time-consuming procedure involving heat treatment at elevated temperatures. In addition, the alloys' maximum deformation is limited, and the materials are expensive. The new polymers can be programmed quickly at milder temperatures, they are much more deformable, and they're less expensive.

A type of plastic that automatically heals cracks in its structure caused by stress, corrosion, and aging was developed at the University of Illinois, Urbana-Champaign, by aeronautical engineering professors Scott R. White and Philippe H. Geubelle; applied mechanics professor Nancy R. Sottos; chemistry and materials science professor Jeffrey S. Moore; and grad students Michael R. Kessler, Suresh R. Sririam, Eric N. Brown, and Sabarivasan Viswanathan [Nature, 409, 794 (2001); C&EN, Feb. 19, page 13]. The plastic contains microcapsules containing a polymerizable liquid. The microcapsules burst when cracks begin to develop, releasing the liquid--which polymerizes when it comes into contact with catalyst molecules dispersed throughout the polymer. This in situ polymerization fills the nascent cracks. Possible applications include a variety of long-lived products--such as electronic circuit boards, aircraft and satellite components, implanted body parts, and adhesives and sealants.

And highly activated polymerization catalysts with higher catalytic activity and efficiency than conventional catalysts were developed by senior research scientist William J. Kruper, scientists Gordon Roof and David R. Wilson, and Eugene Y.-X. Chen (now an assistant chemistry professor at Colorado State University) at Dow Chemical. They used aluminum activators (instead of the usual borane activators) to prepare doubly activated metallocene catalysts--species with two active sites per molecule [J. Am. Chem. Soc., 123, 745 (2001); C&EN, Feb. 19, page 57]. The new catalysts showed a 30-fold enhancement in polymerization efficiency over singly activated analogs--suggesting potential cost savings in plastics manufacturing.


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