Phosphorus-containing aromatic polymers: Synthesis, structure, properties and membrane-based applications

Phosphorus-containing polymers have gained special attention during the past several years as a result of their fascinating properties and wide-ranging applications. The various stable bonding configurations of phosphorus atoms have enabled the synthesis of a large number of stable monomers and polymers with unique and interesting properties, such as improved organo-solubility, good thermal stability, mechanical robustness, and excellent transport characteristics. This in-depth review aims to give an overview of the synthesis and structural modification of various phosphorus-containing polymers and their uses in different membrane-based applications. In the last decade, phosphorus-containing polymers such as polyimide, poly(arylene ether), poly(arylene thioether), poly(arylene ether sulfone), poly(phthalazinone ether), and polytriazole have been used as proton exchange membranes. Subsequently, these phosphorus-based polymers also emerged as an attractive class of polymers for proton exchange membranes due to the outstanding water retention capacity within the membranes as well as well-networked ionic channels for proton conduction, adhesive strength, and peroxide resistance. The incorporation of phosphorus atoms in polymeric materials has also emerged as one of the most effective methods for enhancing the refractive index of polymers. As a result, a large number of research works have been carried out on phosphorus-containing polymers for optical applications. In addition, phosphorus-based polymers have attracted interest in areas such as gas separation and flame retardance. Motivated by these recent developments, this article reviews the synthesis, classification, and structure-property-performance relationships of phosphorus-containing polymers and delineates recent advances in their application in areas such as proton exchange membranes, optoelectronics as well as gas separation applications.