An emulsion

Droplets of an organic molecule can be used to build a polymer to order. Credit: E. Rieger at al./Angew. Chem. Int. Ed.

Chemistry

A shortcut for building a complex molecule

Chemists put carefully crafted mixtures to work to construct specialized polymers.

Sturdy molecular chains called gradient polymers have long proved difficult to synthesize. Now, a team has found a simple way to make them.

Polymers consist of different molecular components strung together randomly or in patterns. In a gradient polymer, the composition gradually transitions along the polymer’s length, from mostly one component to mostly another.

Making gradient polymers is a laborious task. Seeking a fix, a team led by Katharina Landfester and Frederik Wurm at the Max Planck Institute for Polymer Research in Mainz, Germany, sequestered two types of organic molecule in a mixture called an emulsion, in which droplets of one liquid are dispersed throughout another. By exploiting the molecules’ different chemical properties, the researchers were able to dissolve one type in the main liquid and the other in the droplets.

Polymerization began only inside the droplets. As that compound was gradually consumed, the change in concentration pulled ever-greater amounts of the other ingredient into the chains, creating a gradient effect.