Rearrangement in Diamine-Based Polyzwitterion Side Chains for the Modulated pH Responsiveness Regardless of Their Comparable pKa Values.

Carboxylate moieties are appended to different positions of ethylenediamine groups in the polymer side chains, in order to construct the two types of ethylenediamine-based polycarboxybetaine molecules. Antifouling properties and pH-responsiveness of two types of polycarboxybetaine molecules are investigated. Both of them achieve stepwise protonation behavior derived from ethylenediamine moieties, as well as antifouling performance at pH 7.4; however, the pH range in which they exert interaction with polyanion changed considerably, as also suggested by their trend in cellular uptake assay. The obtained results suggest that the position of appended anionic moiety in the diamine-based betaine structure can play important roles in the pH responsiveness and associated interaction with the surrounding substances in biological acidic environments.