Synthesis of pH-and CO2-Responsive Sulfonamide-containing Polymers by RAFT Polymerization

摘要

Recently, much effort has been made toward the synthesis of well-defined (co)polymers capable of rapid, reversible changes in solubility and/or conformation in response to an external stimulus such as pH, temperature, or ionic strength. Of these, pH-responsive polymers have been paid considerable attention for their potential use in drug delivery applications, personal care formulation, and rheology modification. When designing such polymeric systems, it is often imperative that the morphological transitions occur over a very narrow and specific pH range. Commonly, this specificity is achieved via the selection of a monomer with a pKa at or near the target transition pH, but polymer design is accordingly restricted by the limited choice in monomers and their respective pKas. Consequently, a facile method of specifically tuning polymer pH-responsiveness while maintaining a narrow transition range is desired. Herein, we report on the controlled polymerization of a library of sulfonamide-containing methacrylamide monomers via reversible addition-fragmentation chain transfer (RAFT) polymerization. By varying the nature of the sulfonamide substituent, polymer pKa and thus pH-dependent polymer solubility was selectively tuned within the range of biologically relevant pH values (4.5-7.5). Furthermore, the sulfonamide-containing polymers presented exhibited reversible CCh-responsiveness whereby polymers were insoluble in water in the presence of CO2, but regained solubility following CO2 removal via purging with N2.