Cyclodextrin polymers containing ionizable and ionic groups: A comprehensive review from classifications and synthesis methods to applications

Cyclodextrin polymers (CDPs) are a class of polymers that have been extensively used in diverse scientific and technological fields. These polymers are characterized by the presence of cyclodextrins (CDs) as repeating units within their polymeric networks. The unique structure of CDs has enabled the synthesis of CDPs using multifunctional reagents, resulting in an enormous variety of CDPs with diverse structures and properties. This review article focuses on a key subclass of CDPs, namely those containing ionizable and ionic groups (I-CDPs). These polymers can be synthesized by introducing ionizable and ionic groups into the CDPs networks. The first I-CDPs were introduced in 1985, and, since then, there have been significant advances in their synthesis methods and applications. The remarkable features of I-CDPs are their pH-tunable water solubility and high and tunable binding affinity toward various guests, which are difficult to achieve by charge-neutral CDPs. In this review, we categorize I-CDPs into cationic, anionic, and ampholytic polymers and provide an overview of the progress made in their synthesis and applications. We highlight the creative methods used to introduce charged groups into the structure of CDPs and discuss the properties of I-CDPs that make them suitable for diverse applications.