Progress in designing magnetic polymers.

Progress in designing magnetic polymers

As modern alcnemists, organic chemists keep trying to make plastics more like metals -- either to conduct electricity or to serve as magnets. Although several thought they had discovered magnetic organic materials, rarely have these leads panned out (SN: 4/18/87 p.252). However, in the March 27 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, three chemists at Caltech in Pasadena report developing a polymer with promising magnetic potential. Called PMPOT-18, it contains a hexagonal benzene-ring "tail" and a polyene backbone (see diagram).

To be magnetic, a material needs its unpaired electrons to align and spin in the same direction. This alignment, called ferromagnetic coupling, rarely occurs naturally because electrons tend to spin in opposite directions, cancelling out any potential ferromagnetism. But PMPOT-18's structure apparently encourages the necessary coupling. To generate unpaired electrons, Dennis A. Dougherty and two students removed an electron from several electron pairs in the backbone.

This provided magnetic properties in one dimension. "The problem is you need it to be three-dimensional to have a ferromagnet," says Dougherty. The molecules in the polymer also must line up to ensure coupling of electrons between, as well as within, the molecules. The researchers hope to use PMPOT-18's tail to help order the polymer molecules.