Thermoresponsive Polymer Ionic Liquids and Nanostructured Hydrogels Based upon Amphiphilic Polyisobutylene-b-poly(2-ethyl-2-oxazoline) Diblock Copolymers

Abstract

The precise molecular engineering of amphiphilic diblock copolymers as thermoresponsive polymer ionic liquids (PILs) couples polyisobutylene (PIB) and poly(2ethyl-2-oxazoline) (PEtOx) blocks via an imidazolium cation. It enables thermal switching of micellar self-assembly and yields nanostructured hydrogels. Just one ionic liquid (IL)type imidazolium cation is readily incorporated into the backbone of the PIB−IL−PEtOx block copolymers by terminating the cationic 2-ethyl-2-oxazoline (EtOx) ringopening polymerization by alkylation of an imidazoleterminated PIB. The PEtOx block length varies as a function of the PIB-imidazole/EtOx molar ratio and governs solubility, hydrophilic/hydrophobic balance, and nanophase separation. In spite of the presence of highly hydrophobic PIB segments, PIB−IL−PEtOx are rendered water soluble with increasing PEtOx block length and form spherical and elongated micelles as well as hydrogels exhibiting wormlike nanostructures. Furthermore, the lower critical solution temperature of PEtOx segments is the key to thermoresponsive behavior of both water-soluble copolymers and copolymer hydrogels. Owing to low glass temperature and high stability of PIB, these PIB−PILs represent attractive macromolecular nanosystems enabling thermal switching of solubilization, dispersion, transport, and shuttling of molecules and nanoparticles.

Micellization and Adsorption to Carbon Black of Polyisobutylene‐Based Ionic Liquids

“…The CMC is defined as the concentration at which the formation of micelles occurs and is associated with the abrupt transition for a number of physical properties of the system including surface tension, conductivity, and turbidity . A number of other methods are also well suited for the study of reverse micelles including fluorescence spectroscopy, small‐angle X‐ray scattering, conductivity, SLS/DLS, transmission electron microscopy, and transient current …”

“…Their use in a number of application areas, as solvents, dispersants, catalysts, electrolytes, and so forth, has been proposed due to their many advantageous properties, including low melting points, low vapor pressures, excellent thermal stabilities, ease of tunability of properties such as solvency, and ease of preparation . Consistent with the increasing interest in IL, there have been several studies in recent years involving the chain‐end functionalization of PIB with IL moieties to prepare polyisobutylene‐based ILs (PIB‐IL) . These studies have focused on investigating the bulk characteristics of PIB‐IL including the hierarchical structure, viscoelastic behavior, molecular relaxations, and charge transport properties that arise from the ionic moiety.…”

The Importance of Cooperativity in Polymer Blending: Toward Controlling the Thermoresponsive Behavior of Blended Block Copolymer Micelles

“…Considering that a full phase diagram is required in order to characterize a true LCST, the T cp or CST is often referred to instead, and represents the temperature at which macroscopic precipitation occurs at a given concentration and under the chosen experimental conditions 8. Tuning the CST of thermoresponsive polymers is key with regards to their application, and has been found to depend on chemical composition, molecular weight, architecture, block length, concentration, solution state morphology, and pH, amongst other factors 9–15…”

“…[8] Tuning the CST of thermoresponsive polymers is key with regards to their application, and has been found to depend on chemical composition, molecular weight, architecture, block length, concentration, solution state morphology, and pH, amongst other factors. [9][10][11][12][13][14][15] In addition to these variables, the CST can be precisely modulated via the copolymerization of thermoresponsive monomers with either differently responsive or non-responsive monomers, which has distinct advantages over systems composed of homopolymeric blocks. [7,[16][17][18][19][20][21][22][23] However, this technique is somewhat limited for controlling and predicting self-assembly behavior and thermoresponse, with a trial and error approach often required to target specific polymer properties.…”

Nanoconfined Crosslinked Poly(ionic liquid)s with Unprecedented Selective Swelling Properties Obtained by Alkylation in Nanophase-Separated Poly(1-vinylimidazole)-l-poly(tetrahydrofuran) Conetworks

“…Another class of imidazole-based polymers belongs to poly(ionic liquid)s (PILs), that is macromolecules with ionic liquid (IL) moieties. Due to the challenging tasks of the synthesis, revealing the structure–property relationships, and the broad range of special application possibilities, PILs have been intensively investigated in recent years (see e.g., references [ 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 ] and references therein). PILs may find applications in energy production as proton [ 57 ], electron [ 58 , 59 ], or Li-ion [ 60 , 73 ] conducting materials; as metal free [ 61 ] and metal containing [ 62 ] catalysts; gas separation membranes [ 63 , 64 ]; DNA isolation microspheres [ 65 ] etc.…”