Immobilization of polyoxometalates via in-situ protonation and self-gelation of PEG-b-PDMAEMA-b-PTEPM triblock copolymer and its application in selective oxidation

To enrich the building block and function as well as the preparation methodology of metallopolymer system, functioned inorganic polyoxometalate clusters were introduced by using their intrinsic acidity induced multiple interactions with triblock copolymers. In the designed triblock copolymer PEG-b-PDMAEMA-b-PTEPM, the POMs clusters can be immobilized through in-situ protonation of the PDMAEMA block induced electrostatic interaction and the self-gelation of the PTEPM block, while the PEG block can improve the water solubility and dispersion of the final polyoxometalate-based hybrid catalyst (PHC). The selective oxidation activity of PHC is comparable with the homogeneous POMs catalyst as demonstrated by the model reaction of the selective oxidation of methyl phenyl sulfide (MPS) to methyl phenyl sulfoxide (MPSO). By optimizing the ratio between PHC and oxidant H₂O₂, the selectivity for MPSO can achieve as high as 99% with conversion above 95%. Furthermore, the multiple interactions between POMs and the polymer substrate also enhance the stability of PHC and enable the recycling of PHC. Therefore, the methodology of in-situ protonation and self-gelation by the acidity of POMs provides a facile and general strategy to prepare robust POMs-based metallopolymers, paving a new avenue towards cluster-based materials and devices.