Polyimides are proved to be an important class of polymers due to their outstanding set of physical and chemical properties. However, this class of polymers suffers from poor processability, which limits their scope of application. This review article deals with approaches that have been undertaken by different researchers to improve the processability of this class of polymers. Mostly, these are synthetic approaches using new diamine and dianhydride monomers that reduce the interchain interaction of the final poyimide by flexibilizing the polymer chain or increasing the fraction free volume. Accordingly, the structural factors that are responsible for better processability are discussed and representative diamine and diahydride structures are tabulated under different categories. Major efforts towards development of soluble polyimides but maintaining excellent mechanical and thermal properties have been done by our group and are also covered in this article.

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Abstract:In recent years, extensive research on the preparation and properties of proton exchange membranes (PEMs) has been realized. This article focusses on the recent studies on new PEM materials based on aromatic hydrocarbon polymers with sulfonated groups as hydrophilic domains and fluorinated groups as hydrophobic domains as alternatives to conventional perfluorinated polymers. It is necessary to improve the proton conductivity especially under low-humidity conditions and at high operating temperatures to break through the current aromatic PEM system. Hence, there is a need to develop new high-conductivity fuel cell ionomers with improved thermal, chemical, and electrochemical stability by designing a suitable polymer structure for PEM application.