Assembly of Amphiphilic Hyperbranched Polymeric Ionic Liquids in Aqueous Media at Different pH and Ionic Strength

Abstract

We demonstrated the assembly of amphiphilic hyperbranched protic ionic liquids (HBP-ILs) based on aliphatic hyperbranched polyester (HBP) in aqueous media in a wide range of pH and ionic conditions. The series of new branched polyionic liquids with different terminal groups, HBP-ILs, was synthesized by neutralization of carboxylic and sulfonic terminal acid groups of hypebranched core with N-methyl­imidazole (Im) and 1,2,4-1H-triazole (Tr). HBP-IL compounds with triazole and imidazole counterions form 12–16 nm core–corona micelles at pH 11.6. We found that the introduction of long hydrophobic terminal groups such as n-octadecylurethane tails to initial hydrophobic HBP core has larger effect on the size of micellar assemblies than the introduction of ionic terminals groups. Furthermore, tuning the hydrophilic/hydrophobic balance of HBP-ILs can be achieved by changing the degree of ionization of terminal groups and counterions by reducing pH from 11.6 to 5.2 or ionic strength to 0.1 M. These changes caused the formation of much larger micellar aggregates with the size of 150–200 nm due to reduced ionization of carboxylic groups. At the same time, for sulfonate-containing HBP-ILs the micelle size increased modestly (to 25–40 nm) because of the higher degree of ionization of sulfonate terminal groups. The diverse aggregation behavior of these branched polymeric ionic liquids enables control over their micellar morphologies in solution and bulk states.

Self-Assembly of Hyperbranched Protic Poly(ionic liquid)s with Variable Peripheral Amphiphilicity

“…15 We confirm that HBP-ILs form micellar assemblies at low concentration in aqueous media (Figure 3). For example, the CMC values decreased with increasing hydrophobic tails for both CIm n (from 1.4¢10 ¹2 to 3.1¢10 ¹4 mg/ml) and CTr n (from 2.8¢10 ¹2 to 7.1¢10 ¹4 mg/ml) due to the increasing hydrophobicity of HBP-ILs (Scheme 1 and Figure 3).…”

“…The ionic liquid components exploited in this study were imidazole (Im) and triazole (Tr) IL functionalities, which were formed by the neutralization of carboxylic acid groups within branches. 15,19 The hydrophobic terminal groups were n-octadecylurethene arms (Figures S1S12). Hence, the balance of secondary interactions controlling assembly behavior was tuned by varying the relative contributions from these distinct chemical moieties ( Table 1).…”

“…The self-assembly of HBP-ILs in aqueous media at room temperature and neutral pH was performed by the common solvent method for poly(ionic liquid)s. 15 (Figure 1). 4,11 For example, HBP-ILs with imidazolium counterions CIm 32 , CIm 24 , CIm 16 and CIm 8 form assemblies with sizes of 57 « 5, 99 « 5, 160 « 5 and 162 « 30 nm, while those with triazolium counterions CTr 32 , CTr 24 , CTr 16 and CTr 8 form assemblies with sizes of 100 « 10, 147 « 14, 197 « 60 and 240 « 30 nm, respectively ( Figure 1a1c).…”

“…15 Owing to the chemical diversity of the polymerized IL functionalities, a variety of structure directing interactions can be exploited to tune the morphology and properties of the assemblies. 610 For example, by varying the length of the alkyl tails associated with imidazole component®and hence the PIL hydrophobicity®assemblies ranging from unilamellar vesicular to 'onion-like' mesostructures were observed.…”

Synthesis, structure and properties of oligomeric ionic liquids of highly branched structure and special features of their self-arrangement

“…Особливу увагу привертають структури на основі олігомерних іонних рідин (ОІР) та їх полімерних аналогів (ПІР) [1,[3][4][5]. Слід зазначити, що ОІР як окремий напрям у синтезі іономерів уперше було запропоновано нами в роботах [3,5].…”