Hydrophobic Polymer Zwitterions: Impacts of Silylsilane Substitution on Solution and Interfacial Properties.

A new class of zwitterionic polymer amphiphiles was prepared by synthesis and polymerization of novel silyl-substituted sulfobetaine (SB) methacrylate monomers. These silyl-SB methacrylates proved amenable to controlled free radical polymerization methods to afford hydrophobic polymer zwitterions (HPZs) with solubility properties not observed previously for polymer zwitterions (PZs) owing to the dominance of the alkylsilyl groups on solution behavior and surface properties. For example, the solubility profile of HPZs does not overlap with most conventional PZs-they are insoluble in aqueous solutions or trifluoroethanol and instead are soluble in organic solvents such as chloroform and tetrahydrofuran. Interestingly, HPZs exhibited an apparent propensity to form structures in which the zwitterionic components are shielded from the surrounding organic solvent in favor of displaying the alkylsilyl groups. In THF, small-angle X-ray scattering (SAXS) results are characteristic of high aspect ratio (rod- or cylinder-like) structures. Moreover, as thin films HPZs imparted a marked effect on surface properties relative to typical zwitterionic coatings, where the dynamic interplay between hydrophobic and hydrophilic moieties pins water to the surface. This affords surfaces that are simultaneously hydrophobic and water-adhesive, offering an alternative to the types of fluorocarbon-based structures under scrutiny as perfluoroalkyl substances (i.e., PFAS).