Chemistry

A Peek at Polymerization

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Science  13 Aug 2010:
Vol. 329, Issue 5993, pp. 731
DOI: 10.1126/science.329.5993.731-b

The properties of plastics depend intimately on the dynamics of the polymerization reactions used to produce them. Because the reactions are often quite rapid, though, they can prove hard to track. Christianson et al. have adapted a nuclear magnetic resonance (NMR) spectrometer in order to monitor polymerization reactions on a millisecond time scale. Using a stopped-flow approach more common in optical spectroscopy, they set up the probe to acquire data just after pneumatically driven mixing of a catalyst solution stream with a stream of reactive monomer. With this system in hand, they examined the room-temperature polymerization of 1-hexene by a borane-activated zirconium catalyst. They were able to observe initiation and chain propagation steps directly, and also monitor buildup of a transiently deactivated form of the catalyst, resulting from borane binding to a zirconium hydride ligand after chain elimination from the metal center. The results bolster previous mechanistic hypotheses surrounding this catalyst's behavior and highlight the utility of stopped-flow NMR.

J. Am. Chem. Soc. 132, 10.1021/ja105107y (2010).

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