Polypeptide ionic liquid: Synthesis, characterization, and application in single‐walled carbon nanotube dispersion

Abstract

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...

Thermoresponsive poly(γ‐propyl‐l‐glutamate)‐graft‐(oligo ethylene glycol)s: Synthesis, characterization, and properties

“…Pr‐OEG side chains [Figure (a,b)] were prepared form propargyl bromide and oligo ethylene glycols via etherification reactions . PAPLGs [Figure (c)] were synthesized by ring‐opening polymerizations of γ‐chloropropyl‐ l ‐glutamate based N‐carboxyanhydride (CP‐NCA) and postmodification of poly(γ‐chloropropyl‐ l ‐glutamate)s (PCPLGs) with NaN 3 . PAPLGs with different number average molecular weights ( M n s) and molecular weight distributions (PDIs) were obtained by changing initial monomer to initiator ratios (i.e., n‐butylamine) in the ring‐opening polymerization step.…”

“…Poly(γ‐3‐azidopropyl‐ l ‐glutamate) (PAPLG) and propargyl functionalized oligo ethylene glycols (Pr‐OEGs) were synthesized according to a reported procedure. CuBr (99%) and pentamethyldiethylenetriamine (PMDETA, 99%) were purchased from Energy Chemical.…”

Preparation and Thermoresponsive Properties of UCST‐Type Polypeptide Bearing p‐Tolyl Pendants and 3‐Methyl‐1,2,3‐triazolium Linkages in Methanol or Ethanol/Water Solvent Mixtures

“…Deionized water (DI H 2 O) was obtained from Aquapro AR1‐100L‐P11 water‐purification‐system (Ever Young Enterprises Development Co., LTD., P. R. China). Poly(γ‐propyl‐ l ‐glutamate)‐graft‐(4‐methylbenzene) (P1, Scheme ) samples with various number‐average molar masses ( M n s, Table ) were synthesized according to reported procedures …”

“…They have gained increasing attention due to their unique combination of properties including both intrinsic polymer properties (e.g., viscoelastic properties) and IL properties (e.g., ionic conductivity, thermal and chemical stability). A large variety of PILs have been prepared by direct polymerization of IL‐based monomers or postpolymerization chemical modification of polymers with reactive pendants . Recently, thermoresponsive PILs have attracted much attention for their potential applications toward separation, sensors, and biomedicines .…”

Synthesis and solid-state self-assembly of poly(ethylene glycol)-b-poly(γ-benzyl-l-glutamate)s and single-walled carbon nanotubes

“…The integration of SWCNTs with conventional materials especially polymers has been investigated during the past two decades to explore their potential applications in high‐performance composites, sensors, electronic devices, and biological materials . The material properties of these SWCNT‐based nanocomposties are highly dependent on the morphology, SWCNTs orientation, and interfacial contact between the SWCNT and matrices …”