A researcher at Berkeley Lab demonstrates the bulk synthesis of a polysulfate via the SuFEx reaction. Photo: Berkeley Lab.
A researcher at Berkeley Lab demonstrates the bulk synthesis of a polysulfate via the SuFEx reaction. Photo: Berkeley Lab.

A team of researchers has developed a faster and easier way to make sulfur-containing polymers that will lower the cost of large-scale production.

The achievement, reported in papers in Nature Chemistry and Angewandte Chemie, opens the door to creating new products from this class of polymers while producing far less hazardous waste. The researchers' reaction technique, dubbed SuFEx (sulfur(VI) fluoride exchange), combined with a newly identified class of catalysts to speed up the reactions, could be used to make everything from water bottles and mobile phone cases to medical devices and bulletproof glass.

When a useful molecule is discovered, there are only few reactions available to chemists that are simple and efficient enough to meet the requirements for cost-effective industrial production. One option is ‘click chemistry’, which was developed in 2001 by Nobel laureate Barry Sharpless and describes a suite of controllable, highly reactive reactions that are high-yielding and require little-to-no purification.

Following nature's example, click reactions employ simple protocols, use readily available starting materials and work under mild reaction conditions with benign starting reagents. Click chemistry has become a valuable tool for generating large libraries of potentially useful compounds as industries look to discover new drugs and materials.

Scientists at Lawrence Berkeley National Laboratory (Berkeley Lab)'s Molecular Foundry, a facility that specializes in nanoscale science, worked with a team led by Sharpless and Peng Wu, professors at The Scripps Research Institute (TSRI). The team created long chains of linked sulfur-containing molecules, termed polysulfates and polysulfonates, using the new SuFEx click reaction.

"Click chemistry is a powerful tool for materials discovery, but synthetic chemists are often not well-equipped to characterize the polymers they create," said Yi Liu, director of the Organic Synthesis facility at the Molecular Foundry. "We can provide a broad spectrum of expertise and instrumentation that can expand the scope and impact of their research."

The SuFEx reaction, introduced as a new family of click reactions in 2014, reliably and quickly creates new chemical bonds, connecting compounds together with sulfates or sulfonates. While polysulfates have shown great potential as competitors to polycarbonates (strong plastics used for eyewear lenses and water bottles, for example), they have rarely been used for industrial applications due to a lack of reliable and easily scalable production processes.

To overcome the challenges of mass-manufacturing polysulfates and polysulfonates, the TSRI team explored various catalysts and starting reagents to optimize the SuFEx reaction. For this, they relied on their collaborators at the Molecular Foundry to assess physical properties and determine if the newly created polymers were thermally stable.

Polymers are assembled from smaller molecules – like stringing a repeating pattern of beads on a necklace. In creating a polysulfonate ‘necklace’ with SuFEx, the researchers identified ethenesulfonyl fluoride-amine/aniline and bisphenol ether as good ‘beads’ and found that using bifluoride salt as a catalyst made the previously slow reaction ‘click’ into action. The researchers found that the high efficiency of the reaction resulted in a remarkable 99% conversion, from starting reactants to products, in less than an hour.

They also found that the new reaction requires 100 to 1000 times less catalyst than other known methods, resulting in significantly less hazardous waste. In addition, bifluoride salts are much less corrosive than previously used catalysts, allowing for a wider range of starting substrate ‘beads’, which could lead to its adoption for a wide range of industrial processes.

"There are many new polymers that haven't been widely used by industry before," said Liu. "By reducing waste and improving product purity, we lower the cost and make this reaction much more industry friendly."

This story is adapted from material from Lawrence Berkeley National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.