Optimizing Fouling Resistance of Poly(Sulfabetaine)s through Backbone and Charge Separation

Abstract

The three dominating polyzwitterion families, polyphosphatidylcholines, polycarboxybetaines, and polysulfobetaines, all of which provide high fouling resistance, have been complemented by a fourth one recently, the so-called polysulfabetaines that combine ammonium with sulfate moieties. To elucidate the relationship between their structure and antifouling potential, coatings of a set of systematically varied poly(sulfabetaine methacrylate)s are investigated. In particular, the effects of the spacer groups, either separating the zwitterionic units from the polymer backbone, or the cationic from the anionic charges, are explored, studying the resistance against non-specific protein adsorption and the accumulation of single species of marine biofouling organisms. All polysulfabetaines are at least as effective, or even more potent than the structurally closely related standard poly(sulfobetaine methacrylate). Their resistance against proteins and fouling organisms can be tuned via the betaine-to-backbone spacer. Overall, the polysulfabetaine coatings with the shorter ethylene spacer show higher resistance against non-specific adsorption of proteins, in particular of lysozyme, or against colonization by diatoms. This may result from the higher steric constraints of the polymer attached zwitterions, favoring particularly advantageous conformations. Moreover, a shorter spacer between the oppositely charged ionic groups of the zwitterionic moiety reduces the settlement of cyprid larvae more effectively.