Molecular Design of Zwitterionic Polymer Interfaces: Searching for the

Invited Feature Article Cite This: Langmuir XXXX, XXX, XXX−XXX

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Molecular Design of Zwitterionic Polymer Interfaces: Searching for the Difference Andre ́ Laschewsky*,†,‡ and Axel Rosenhahn*,§ †

Institut für Chemie, Universität Potsdam, Karl-Liebknechtstr. 24-25, 14476 Potsdam-Golm, Germany Fraunhofer Institute for Applied Polymer Research IAP, Geiselbergstr. 69, 14476 Potsdam-Golm, Germany § Analytische Chemie−Biogrenzflächen, Ruhr-Universität Bochum, Universitätsstr. 150 NC, 44801 Bochum, Germany

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ABSTRACT: The widespread occurrence of zwitterionic compounds in nature has incited their frequent use in designing biomimetic materials. Therefore, zwitterionic polymers are a thriving field. A particular interest for this particular polymer class has currently focused on their use in establishing neutral, low-fouling surfaces. After highlighting strategies to prepare model zwitterionic surfaces as well as those that are more suitable for practical purposes relying strongly on radical polymerization methods, we present recent efforts to diversify the structure of the hitherto quite limited variety of zwitterionic monomers and of the derived polymers. We identify key structural variables, consider their influence on essential properties such as overall hydrophilicity and long-term stability, and discuss promising targets for the synthesis of new variants.

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INTRODUCTION Featuring many properties of both ionic and nonionic polymers, zwitterionic polymers exhibit a unique property profile, e.g., combining charge neutrality with high hydrophilicity.1−4 Formally, IUPAC defines zwitterionic polymers, or synonymously polymeric inner salts, as a subclass of ampholytic polymers that contain ionic groups of opposite sign on the same pendant groups. The underlying ampholytic polymers are defined as polyelectrolytes composed of macromolecules containing both cationic and anionic groups (generally not in equal numbers) or corresponding ionizable groups. Accordingly, polyzwitterions are distinguished from common polyampholytes on the one hand by their inherent fully balanced charge without low-molar-mass counterions being present even at a very small length scale (