A different class

Using building blocks that make up ordinary plastics, but putting them together in a whole new way, University of Michigan researchers have created a class of lightweight, rigid polymers they predict will be useful for storing hydrogen fuel. The work is described in the current issue of the journal Science.

The trick to making the new materials, called covalent organic frameworks (COFs), was coaxing them to assume predictable crystal structures, something that never had been done with rigid plastics.

"Normally, rigid plastics are synthesised by rapid reactions that randomly cross-link polymers," said postdoctoral fellow Adrien Côté, who is first author on the Science paper. "Just as in anything you might do, if you do it really fast, it can get disorganised." For that reason, the exact internal structures of such materials are poorly understood, making it difficult to predict their properties. But Côté and colleagues tweaked reaction conditions to slow down the process, allowing the materials to crystallise in an organised fashion instead of assembling helter skelter.