Polymers acquire fire resistance and durability with a light chemical upgrade

As the demand for advanced polymers materials increases, post-functionalization has become an effective strategy for designing functional polymers. This approach consists in modifying existing polymers channels by introducing new chemical groups after their synthesis, allowing the transformation of polymers easily available in materials with desirable properties.

Post-functionalization can be carried out under soft conditions using visible light in the presence of catalysts, which provides a lasting way to develop polymers of large value. However, existing methods are often based on the generation of carbon radicals along the polymer chain, limiting the variety of functional groups that can be introduced.

In an important progression, a team led by Professor Shinsuke Inagi of the Department of Chemicals and Engineering Sciences, the School of Materials and Chemical Technologies of the Institute of Tokyo Sciences (Science Tokyo), Japan, has developed a post-funionalization technique which allows the incorporation of phosphonate esters in visible light conditions. This breakthrough opens the way to a larger range of polymer changes.

Study, published Online in the newspaper International edition of Angewandte Chemie On May 15, 2025, was an effort of collaboration involving Inagi and former graduate student Mr. Tomohiro Tamano of Science Tokyo, in partnership with Professor Hirohisa Ohmiya from the University of Kyoto.

The reaction is based on the chemistry of the radical-polar cross (RPC), in which a carbocation is generated on the skeleton of the polymer, allowing reactions with various nucleophiles. “Our strategy is the first example of postfunctionalization using an RPC process catalyzed by organophotoredox, considerably expanding the scope of reactions and allowing the creation of new polymer architectures which are inaccessible by other methods”, explains Inagi.

The process implies the phosphonylation of poly (methacrylate) derivatives containing a group of phtalimide, using the organophotorous catalyst 12-phenyl-12h-benzo[b]PHENOTHIAZINE (PH-Benzoptz). The proposed reaction mechanism begins with the formation of a donor-acceptor complex (EDA) between the phtalimide ester and the catalyst.

During the irradiation with a blue LED light, the catalyst gives an electron to Ester, causing the rupture of the phtalimide group with carbon dioxide, which generates a radical centered on carbon on the polymer chain. This radical then undergoes an additional transfer or coupling of electrons with the radical cation of the catalyst, forming a carbocation equivalent (a positively loaded intermediary) on the polymer chain.

Finally, this intermediary reacts with the phosphites of testiskyl (acting as nucleophiles), resulting in the incorporation of phosphonate groups into the polymer chain.

The resulting polymer, including isopropenylphosphonate of diethyl, propylene and methyl acrylate units, has a unique composition which is difficult to reach using standard radical polymerization techniques. The team also managed to incorporate phosphites of tests into a precursor polymer composed of phtalimide and styrene monomers. They have also created new polymers with functionalization degrees ranging from 7% to 21%, using various Trialyl phosphites, including variants of chloro- trifluoromethyl-substitutes, demonstrating the wide range and flexibility of the method.

“Copolymerization olefins with activated vinyl monomers are difficult and often lead to a low incorporation of olefine, even in severe radical polymerization conditions. However, our post-functionalization strategy allows the introduction of phosphonate groups in the Oléfine-Metacrylate copolymers, facilitating the development of unique polymers structures and useful, “said in Inagi.

Polymers with Ester groups of phosphonate have fire resistance and temperature responsiveness, even low content from 10% to 20%. Consequently, this proposed post-functionalization strategy could be beneficial to develop fireproof materials and additives for lithium-ion batteries, helping to prevent battery fires. The team now aims to apply this strategy to integrate other useful chemical groups in polymers for a lasting path to the development of new generation functional materials.