little is known about the effects of PIL topology on bactericidal properties.Due to the absence of chain ends and steric constraints, cyclic polymers are one of the most intriguing nonlinear polymer topologies because they exhibit distinct properties in comparison with their linear counterparts. [9] For instance, Grayson and coworkers demonstrated that cyclic poly(ethylene imine) (PEI) exhibits a higher transfection efficiency when compared to its linear PEI analog in addition to reduced toxicity relative to the branched PEI "goldstandard" control. [10] Recent studies have also suggested that a cyclic hydrophilic moiety offers greater stability for selfassembled micelles than a linear analog. [11] In particular, the Benetti group studied how the topology effects typically displayed by cyclic poly(2-ethyl-2-oxazoline) (PEOXA) in solution manifested for brush assemblies generated on surfaces. It was demonstrated that the topological effects of the brush assemblies imparted by the cyclic polymer architecture translated into an enhancement of the brush properties, such as steric stabilization of surfaces, antifouling and lubricating behavior. [12] Inspired by these advances, in this study, we focused on the preparation of cyclic PIL brushes by the "grafting to" technique and systematically compared the bactericidal activity of linear brush analogs. In particular, the objective of this work was to explore whether the cyclic PIL architecture would impart PILs with enhanced properties in bactericidal activity, thus expanding the design possibilities for the development of excellent antibacterial surfaces.Herein, well-defined linear PIL adsorbates, in which the tertbutyldimethylsilyl ether and sulfonyl fluoride groups are at the α and ω positions of the polymer chains, were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using a heterodifunctional trithiocarbonate RAFT agent (Scheme 1). Cyclic PIL adsorbates were then conveniently obtained by intramolecular sulfur(VI)-fluoride exchange (SuFEx) click cyclization of the linear PILs in air at room temperature. In particular, both linear and cyclic PILs contain catechol groups that allow them to be efficiently grafted onto gold surfaces. [13] Subsequently, the morphologies of cyclic PIL brushes were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The topological effects of cyclic PIL brushes on bactericidal activity were evaluated using the most common catheter-associated urinary tract infection pathogen-Escherichia coli [14] -and compared with those of the respective linear precursor.In addition to extensive studies of conventional linear poly(ionic liquids) (PILs), exploration of the effects of PIL topology, especially cyclic architecture, on bactericidal properties will expand the design possibilities for the development of excellent antibacterial surfaces. Herein, the preparation of antibacterial surfaces based on cyclic PIL brushes is reported for the first time and how the cyclic PIL architec...