Making polysulfates and polysulfonates

RESEARCHERS using so-called “click chemistry” say they have developed a fast, easy way to make sulfur-containing polymers that could lower the cost of large-scale production.

The process could also pave the way for developing innovative products and reducing hazardous waste.

Click chemistry describes a suite of reactions that are controllable, highly reactive, high-yielding, and require little purification. Protocols are usually simple, using readily-available starting materials, and work under mild reaction conditions with benign reagents.

Now, researchers from China and the US have optimised one such reaction, known as SuFEx (sulfur(VI) fluoride exchange). They believe their work will lower the cost of large-scale production of polysulfates and polysulfonates, which are potential competitors to polycarbonate plastics, but typically challenging to manufacture. Their work is published over two articles in Nature Chemistry and Angewandte Chemie.

To optimise the process, the team tested various catalysts and starting reagents, and then assessed physical and thermal properties of the newly-created polymers. They identified ethenesulfonyl fluoride-amine/aniline and bisphenol ether as good monomers, and found that using bifluoride salt as a catalyst made the previously slow reaction “click” into action. Polysulfates and polysulfonates with high molecular weight, narrow polydispersity and excellent functional group tolerance were created.

The new reaction was reported as achieving 99% conversion of starting reactants to products in less than an hour. Furthermore, it required 100–1,000 times less catalyst than other known methods, resulting in significantly less hazardous waste.

The authors state in their Nature Communications paper that the process has now been made practical, with regard to the reduced cost of catalyst, polymer purification and by-product recycling. They also comment that the process is not sensitive to scaleup, which is essential for its future translation from laboratory research to industrial applications.

Bifluoride salts are also relatively less corrosive than previously-used catalysts, which the group says would allow for a wider range of starting substrate monomers, increasing the potential breadth of industrial process applications.

Co-author Yi Liu from the US’ Lawrence Berkley Laboratory Molecular Foundry said: “There are many new polymers that haven't been widely used by industry before. By reducing waste and improving product purity, we lower the cost and make this reaction much more industry friendly.”

Nature Chemistry: http://doi.org/b9zb

Angewandte Chemie: http://doi.org/b9zc