Developing the inherent functionality of highly pure porous organic polymers

A group of researchers from Tohoku University developed a method for synthesizing a special type of polymer that has applications for reducing greenhouse gas emissions -- a major concern amidst a period of rapid climate change.

Porous organic polymers (POPs) are like sponges. Their high porosity allows them to soak up harmful pollutants like carbon dioxide (CO2). They also boast high thermal and chemical stability, giving POPs the potential to be applied to a wide range of fields, such as gas separation and energy storage.

Previously, POPs were synthesized via oxidation reactions using metal salts as oxidants or coupling reactions using organometallic catalysts. However, these oxidants and catalysts usually remain as metal impurities within the pores of POPs -- decreasing its porosity and overall usefulness. It would be like trying to clean dishes with a sponge that is already dirty. To avoid this, we need a way to produce highly pure (squeaky clean) POPs with no residual impurities.

A group of researchers from Tohoku University developed a method for synthesizing POPs using iodine as an oxidant to minimize residual impurities. They found that iodine and iodine-derived impurities were completely removed by washing it with ethanol after synthesis, and highly pure POPs (polytriphenylamine derivatives) with no residual impurities were successfully obtained. The obtained POPs exhibited the highest specific surface area among reported POPs containing triphenylamine.

As shown in Figure 1, TTPA was polymerized by stirring it and iodine in 1,2-dichloroethane. Specifically, as shown in Table 1, to investigate the influence of reaction conditions on the resulting polymer, the iodine amount and reaction temperature varied. After polymerization, the precipitated pTTPA was collected via filtration and washed with ethanol to obtain pale-yellow pTTPA powders, denoted as pTTPAs 1–7.

"As expected, reducing the impurities improved the porosity, which lead to better performance in measures such as CO2 adsorption capacity," explains Kouki Oka (Tohoku University), "Furthermore, they exhibited their inherent functionalities for the first time, such as proton conductivity and unique gas adsorption behavior accompanied by the gate-opening phenomenon. This is exciting because it indicates the potential for novel applications of POPs as fuel cells and adsorbents."

This new finding indicates that synthesizing highly pure POPs enables the realization and development of organic materials with their inherent functionality. As greenhouse gas emissions continue to be a problem, researching innovative and effective solutions such as POPs will continue to be an important endeavor for researchers.

Source: http://dx.doi.org/10.1002/smll.202410794