Polymer ionic liquids (PILs) are a type of polyelectrolytes containing ionic liquid species (e.g., imidazolium, pyridinium, hexafluorophosphate and triflates) in the main chain or the side chain.1 They have shown interesting physical properties, including conductivity and low glass transition temperature, which depends strongly on polymer primary and secondary structures, architectures, and so forth.2 Increasing attention has been paid for their potential applications in different fields, such as energy, 3,4 catalysis, 5,6 and biomedical applications. 7,8 Up to date, a variety of main-chain and side-chain PILs have been synthesized by chain-growth or step-growth polymerizations.1,9-12 Meanwhile, diverse types of synthetic polymers (e.g., polyimides, 11 polyolefins, 13,14 and conjugated polymers 15,16 ) have been integrated with ionic liquid groups for versatile uses.Polypeptides are mimics of natural peptides and able to form stable secondary structures (e.g., a-helices and b-sheets) in solution and solid state. [17][18][19] They are biocompatible and can be readily prepared in a large scale by ring-opening polymerization of N-carboxyanhydride (NCA) monomers. 20,21 When helical polypeptides conjugated with functional moieties (e.g., saccharide [22][23][24] and oligo-ethylene-glycol), 25,26 they demonstrated promising properties, such as molecular recognition and thermoresponsive property, which are associated with their unique spatial organization of surface moieties.Here, we report the design and synthesis of polypeptide ionic liquids and evaluation of their potential application for the dispersion of single-walled carbon nanotubes (SWCNTs), aiming to develop a new class of polymeric materials. These polypeptide ionic liquids adopt a-helical conformation in solid state and solution and show superior SWCNT dispersibility in water. To the best of our knowledge, this is the first example of polypeptide ionic liquid adopting a-helical conformation.c-Chloropropyl-L-glutamate-based N-carboxyanhydride (CP-NCA, 2, Supporting Information Fig. S1) was first synthesized in two steps from L-glutamic acid with an overall yield of 40-50% (Scheme 1). Typically, c-chloropropyl-L-glutamate (CP-Glu, 1) was synthesized by monoesterification of L-glutamic acid with 3-chloropropanol in the presence of sulfuric acid instead of chlorotrimethylsilane 22 at room temperature. Then, 1 was cyclized with triphosgene at room temperature in anhydrous THF to afford 2.A series of poly(c-chloropropyl-L-glutamate)s [PCPLGs, 3, Supporting Information Fig. S2(A)] with different number average molecular weights (M n s) and molecular weight distributions (PDIs) were then synthesized by ring-opening polymerization of CP-NCAs with different initial monomer to initiator (i.e., n-butylamine instead of hexamethyldisilazane 22 ) ratios or using triethylamine as the initiators to achieve the highest M n .27 The M n s of PCPLGs were revealed by gel permeation chromatography (GPC, Supporting Information Fig. S3). While we have attempted to prepare polypeptid...