A simple method to obtain versatile porous polymers


Researchers at SIT, Japan find that adding water to a triaziridine compound at mild temperatures is enough to produce strong, cohesive porous polymers. By adjusting the reaction temperature and the initial triaziridine concentration, the morphological and mechanical characteristics of the polymers can be controlled. Credit: American Chemical Society.

For a polymer composed of very simple repeating units, polyethyleneimine (PEI) has an incredible number of practical applications, including detergents, adhesives, cosmetics, industrial agents, CO2 capture, and even cell cultures. In general, PEI is synthesized by the ring-opening polymerization of ethylenimine, also known as aziridine. When produced in this way, the result is a liquid polymer with a branched structure.

Despite its enormous potential, P.E.I. is hampered by the fact that ethylenimine is a highly toxic substance. Because this precursor is not commercially available, it is quite difficult to conduct experiments aimed at controlling the morphology or state of the PEI. Therefore, we might miss many new apps for PEI.

To solve this problem, a research team from the Shibaura Institute of Technology (SIT), Japan, focused on the development of new network polymers based on PEI. Led by Professor Naofumi Naga of the SIT Graduate School of Engineering and Science, this team recently discovered a simple but revolutionary way to produce such polymers from a triaziridine compound; their suggestion – just add a little water. This study, posted online on April 12, 2022 and then published in volume 11 number 5 of ACS macro letters on May 17, 2022, was carried out in collaboration with Professor Tamaki Nakano from the Institute of Catalysis and the Graduate School of Chemical Sciences and Engineering, Hokkaido University, Japan, as part of the Joint Usage/Research Center Program (MEXT).

Although the researchers tested two triaziridine compounds, only one of them was able to consistently produce a porous polymer network after reacting with water. Its full chemical name is 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] and it can be abbreviated as “3AZ”. The team found that dissolving 3AZ in distilled water at temperatures between 20 and 50°C was enough to open the aziridine groups and bond the 3AZ monomers together. The result, under most temperatures and initial concentrations of 3AZ, was a porous polymer phase.

The team analyzed the morphology of porous polymers by scanning electron microscopy. While synthesis temperature seemed to play no role in this regard, different concentrations of 3AZ resulted in different particle sizes, ranging from 1 to 5 μm. On the contrary, the synthesis temperature affected some of the mechanical properties of the porous polymers, such as their Young’s modulus (elasticity). Notably, all porous polymers were able to withstand 50 N compression tests.

Being able to adapt the morphological and mechanical characteristics of porous polymers based on PEI is a big advantage, especially when it is enough to adjust a simple reaction with water. “Water is an ideal solvent for chemistry because of its environmental friendliness, availability and durability,” Prof. Naga remarks, “Our paper reports one of the simplest methods for obtaining a network polymer based on PEI known to date.” In addition to the versatile properties, the team found that their porous polymers could absorb various solvents regardless of their characteristics, including hexane, acetone, ethanol, dichloromethane and chloroform.

Overall, this study will hopefully put new PEI-based polymers in the limelight. Looking to the future, Professor Naga and his colleagues expect to find new uses for these compounds. “Processing and chemical modification of porous 3AZ polymers will likely expand their areas of application, and research into these aspects is already underway,” he concludes.

Improved method for making branched polymers

More information:
Naofumi Naga et al, Ring-opening polymerization of triaziridine compounds in water: an extremely simple method to synthesize a porous polymer by polymerization-induced phase separation, ACS macro letters (2022). DOI: 10.1021/acsmacrolett.2c00110

Provided by Shibaura Institute of Technology

Quote: Just Add Water: A Simple Method to Obtain Versatile Porous Polymers (July 11, 2022) Retrieved August 9, 2022 from https://phys.org/news/2022-07-simple-method-versatile -porous-polymers.html

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