Electricity
The future of the billions of tonnes of plastics produced every year around the world could be even more diverse with the rise of radical polymers.
Radical polymers are an emerging category of electrically-conductive plastics that could bring about more cost-efficient, transparent solar cells, flexible and lightweight batteries and super-thin antistatic coatings for consumer electronics and aerospace applications.
Researchers at Purdue University, Indiana, have established the solid-state electrical properties of PTMA, an inexpensive, transparent plastic that resembles Plexiglas, but is around 10 times more electrically conductive than common semi-conducting polymers. These findings have been published in the journal Macromolecules, while the American Chemical Society has also recorded a series of podcasts with one of the study's authors.
Assistant Professor of Chemical Engineering at the university Bryan Boudouris explained: "[PTMA is] a polymer glass that conducts charge, which seems like a contradiction because glasses are usually insulators."
PTMA is in a category of electrically-active polymers that could bring about a range of opportunities including inexpensive, transparent solar cells, antistatic coverings for aircraft to protect against lightning strikes, antistatic and antiglare coatings for mobile phone displays, flexible computer flash drives and thermostatic devices that can generate electricity from heat.
PTMA has been utilised commercially in certain kinds of batteries, but finding widespread applications for the polymers will require increasing the conductivity capabilities to up to 1,000 times what they can conduct at present, Boudouris stated.
The molecular structure of polymers contains a backbone and may contain side chains - also known as pendant groups - that hang from the central structure. In radical polymers, these pendant groups allow a charge to be transported, conducting current.
To create a radical polymer, the researchers at Purdue used a process called deprotection, which involved replacing a specific hydrogen atom in the pendant group with an oxygen atom, converting it into a radical. Electrons surround an atom's nucleus in 'shells' and these electrons are usually paired. The oxygen atom in PTMA, however, has one unpaired electron in its outer shell, making it amendable to transporting charge.
Boudouris said: "We just finally studied deprotection in a way others had not to learn how it affects the electronic properties of the radical polymers. You have to control the deprotection process very well because it makes the conductivity vary by orders of magnitude."
The team has determined that taking this deprotection step can lead to four distinct chemical functionalities of the radical polymer, two of which are promising for increasing the conductivity of the polymer.
"Manipulating the reaction conditions for this deprotection step, and monitoring closely the resultant chemical functionalities, is critical in tuning the electrical properties of radical polymers," Boudouris said.
"We make billions of tonnes of plastic every year," he continued. "So imagine if you could produce that same kind of material at that same scale but now it has electronic properties."
The article in Macromolecules was authored by Purdue graduate students Edward Tomlinson, Martha Hay and Boudouris, who was also involved in the original research article published in May and co-authored with Lizbeth Rostro and Si Hui Wong.
Research is ongoing and has received funding from the National Science Foundation (NSF), the Air Force Office of Scientific Research (AFOSR) and the Defense Advanced Research Projects Agency (DARPA).