Designer Agents Modify Polymers

MACROMOLECULAR SCIENCE

A new family of "designer" nucleating agents selectively and efficiently nucleates the growth of different crystal structures of isotactic polypropylene, imparting drastically improved physical properties, according to scientists in Europe. The compounds--substituted 1,3,5-benzenetrisamides--were discovered by researchers at Bayreuth University, in Germany; the Swiss Federal Institute of Technology (ETH), Zurich; and Ciba Specialty Chemicals, Basel, Switzerland (Macromolecules 2005, 38, 3688).

"There is a pressing need to improve properties of mass-produced materials, such as bulk polymers, to more efficiently use the precious resources from which they are made," observes ETH professor of polymer technology Paul Smith. Additives are commonly used to enhance nucleation of crystal growth and, therefore, the rate of production of polymer artifacts, and to improve material characteristics, he says.

"Isotactic polypropylene is one of the premier industrial polymers," he continues. "Our new family of compounds permits us to process this polymer into articles that exhibit an extraordinary range of physical properties."

The compounds are stable to temperatures well above 300 ^oC. The team showed that by selecting appropriate substituents, it is possible to nucleate the common *-modification of the polymer and render the material, which is normally turbid, highly transparent.

"Remarkably, the concentration of additive needed to achieve this result is about one-tenth of that required using current additives," notes Bayreuth professor of macromolecular chemistry Hans-Werner Schmidt.

Other trisamide derivatives induce the formation of the mechanically distinct, tough, and impact-resistant β-polymorph of isotactic polypropylene.

"We feel that, with this work, part of the black art of modifying bulk polymers through the use of additives has been put on a more solid scientific base, and we expect our approach to the design and tailoring of additives to perform specific tasks to be of broader use," Smith says.