Post-Polymerization Modification of Polystyrene through Mn-Catalyzed Phosphorylation of Aromatic C(sp²)–H Bonds

The high flammability and lack of charrability of polystyrene (PS) pose significant limitations on its broader applications. Therefore, there is an urgent need for a straightforward and efficient method for the synthesis of flame-retardant PS, which still poses a considerable challenge. In this study, we present an efficient approach to enhance the flame-retardant properties of PS through direct phosphorylation of aromatic C(sp 2 )–H bonds using commercially available and inexpensive manganese catalyst. A range of phosphonates served as reactive substrates to enable a tunable degree of polymer functionalization. The corresponding phosphorylated PS specimens were determined by means of 1 H NMR, 31 P NMR, FTIR spectroscopy, and size exclusion chromatography. Microscale combustion calorimetry tests indicate that this protocol indeed enhances the flame-retardant performance of PS. Moreover, other advantages associated with the incorporation of the phosphonate group have been observed, including maintained thermal resistance and improved wettability. This cost-effective strategy of Mn-catalyzed C–H can also be utilized to directly obtain phosphonate modification of waste foamed PS and styrene acrylonitrile copolymer, providing a method for the purpose of recycling and upgrading PS plastics.