Electrically conductive plastics, also known as conjugated polymers, bring many cutting-edge benefits for flexible sensors, medical devices, energy-storage systems and more. They are currently produced at relatively small volumes and come with extremely high prices. A novel technology discovered at the Chalmers University of Technology (Gothenburg, Sweden; www.chalmers.se) promises to produce conjugated polymers more efficiently, safely and at much larger volumes than conventional manufacturing techniques. “The most widely used method to produce many high-performance conductive plastics requires toxic precursors. Our process avoids those precursors,” explains Christian Müller, professor at Chalmers’ Department of Chemistry and Chemical Engineering, adding that the process functions at room temperature and requires no heating or inert atmosphere, unlike other methods. “The combination of these features allows us to carry out the production at a much larger scale. This has not been possible up to now,” he notes.
Employing a palladium catalysis scheme that supports the reaction at ambient temperature and open air, the technology involves direct arylation to couple the monomers (thienothiophene and bithiophene — the basic building blocks of many organic semiconductors) together in the solvent N-butyl-2-pyrrolidone. The resulting deep-purple solution is then washed to remove impurities, and the solvents are removed using rotary evaporation, finally yielding a glittery, gold conductive plastic material (photo).
“We have already demonstrated that our process can be carried out in continuous flow. This has not been possible with direct arylation polymerization until now. Continuous-flow processing will allow us to further improve scalability and reproducibility,” says Müller. The research team at Chalmers has created 100-g batches of the conductive plastics, which Müller notes is “100 to 1,000 times larger than what is typically done in research labs.”