The synthesis of L-serine-based zwitterionic polymers, poly(L-serinyl acrylate)s (PSAs), of controllable molecular weights and low polydispersities via reversible addition−fragmentation chain transfer (RAFT) polymerization in water at 70°C is described. The obtained homopolymer PSA exhibits dual responsiveness toward pH and temperature in aqueous solution. The PSA exhibits an isoelectric point near pH 2.85 where the PSA molecules exist in its zwitterionic form. In the pH range of 2.3−3.5, the aqueous PSA solution appears as a two-phase system due to the formation of insoluble aggregates through the intra-and intermolecular electrostatic interaction between the pendent ammonium and carboxylate groups of the neighboring zwitterionic PSA molecules. Furthermore, in this pH range, the two-phase PSA solution becomes one-phase upon heating, exhibiting distinct reversible upper critical solution temperature (UCST)-type phase transition. The cloud point (T p ) is found to increase with increasing molecular weights of PSAs. It is also observed that the T p changes with changing the solution pH, exhibiting highest T p near the isoelectric point of PSA. Addition of an electrolyte such as brine solution also affects the T p of PSA solution following the antipolyelectrolyte effect. Finally, fluorescein isothiocyanate (FITC) tagged PSA with dual-responsiveness is prepared by the postmodification of pendent amino groups of PSA for futuristic applications in biosensors and bioimaging.

Poly(triphenyl-4-vinylbenzylphosphonium chloride) synthesized via RAFT polymerization exhibits both tunable halide ion- and thermo-responsiveness (UCST-type) in aqueous solution and acts as a thermosensitive stabilizer for carbon nanotubes.

A series of monomers comprising units bearing both imidazolium bromide ionic liquid (IL) and zwitterionic imidazolium alkyl carboxylate moieties with different alkyl spacer groups are designed and synthesized. RAFT polymerization of these monomers produces a new class of ionic homopolymers, named poly­(zwitterionic ionic liquid)­s (PZILs), which behave like poly­(ionic liquid)­s as well as poly­(zwitterion)­s depending on the solution pH. Such PZILs exhibit an isoelectric point (pI) at pH 5.7, where they exist in their zwitterionic form, making them dual responsive to both pH and temperature. Above pH 5, the aqueous transparent solution of PZIL transforms into turbid suspension due to the formation of insoluble hierarchical nanoaggregates (NAs) of various morphologies such as small spheres, large spheres, flower-like, dendrite-shaped, and dendritic fibril-like depending upon the solution pH and PZILs’ structures. The dissolution of aggregates upon heating and reaggregation upon cooling suggests existence of reversible upper critical solution temperature (UCST)-type phase transition above pH 5. Below pH 5, owing to the presence of cationic IL moieties, aqueous PZIL solution exhibits transparent-to-turbid transition due to the formation of anion-induced NAs of various dendritic morphologies upon addition of various chaotropic anions within the Hofmeister series. Upon heating, this colloidal turbid suspension becomes transparent, showing a distinct UCST-type phase transition, and the process is reversible. It is easily possible to fine-tune the cloud point and morphologies of the NAs by changing various parameters such as molecular weight, concentrations, structure of PZILs, nature and concentration of anions, and solution pH.

Considering the great potential of layered transition-metal dichalcogenides in thin film photovoltaic, advanced composite materials, and biomedical applications, it is of high importance to have a highly efficient method for their generation in both aqueous and nonaqueous media. Here, we demonstrate a simple one-pot efficient exfoliation approach to prepare dispersion of single or few-layers MoS 2 nanosheets by quick sonication in the presence of cationic poly(ionic liquids)s (PILs) in both aqueous and nonaqueous media at room temperature. These PILs are synthesized by simple conventional free radical polymerization from designed ionic liquid monomers. This method is extendable for efficient generation of MoSe 2 nanosheets' dispersion in these solvents. Owing to the solubility in both water and organic solvents, cationic PIL molecules serve the dual purpose of an exfoliating-cum-stabilizing agent. PIL-stabilized nanosheets' dispersions are stable for more than two months at ambient temperature. The adsorption of PIL to the surface of MoS 2 nanosheet converts them to responsive toward ions and temperature in aqueous medium. Additionally, MoS 2 −PIL nanosheets can easily be dispersed in water-soluble poly(vinyl alcohol) and nonaqueous-soluble poly(methyl methacrylate) matrices for making well-dispersed homogeneous nanocomposites and their dielectric properties are studied.

This contribution describes the synthesis of 3-alkyl-1-vinylimidazolium bromide ionic liquid monomers (ILMs), ion exchange with bis­(trifluoro­methane)­sulfonimide anion (NTf2 –), and their radical polymerization to a homologous series of poly­(ionic liquid)­s (PILs) containing an imidazolium ion substituted with alkyl chains of different lengths (C2(n=7–11)). Owing to the presence of a long alkyl chain, all the ILMs show crystalline phases whose melting point and melting enthalpy increase sharply with increasing alkyl chain length, and those parameters decrease upon replacing Br– with a NTf2 – anion. In addition to the solid crystalline phase, the ILMs with a Br– ion only show liquid crystalline mesophases above the melting of solid crystals. The corresponding PILs are semicrystalline in nature due to crystallizable alkyl side chain showing similar chain length and counteranion-dependent melting behaviors with poor crystallinity compared to those of ILMs. The formation of strong birefringent crystals of various morphologies including Maltese-cross and ring-banded spherulites is observed for ILMs. However, the corresponding PILs with a Br– ion show crystals with fibrillar morphology with weak birefringence, but surprisingly such fibrils are not observed for PILs with a NTf2 – ion. The influence of structural modulations of ILMs and their corresponding PILs on their ionic conductivities is also investigated. Moreover, PILs with a Br– ion exhibit an upper critical solution temperature (UCST)-type turbid-to-transparent phase transition in CHCl3 with tunable cloud point as observed from turbidity and calorimetric measurements. Such a thermoresponsive solution phase behavior is totally absent for PILs when Br– is replaced with a NTf2 – ion.

The synthesis of a series of dual thermosensitive nonionic−ionic random copolymers with varying compositions by reversible addition−fragmentation chain transfer polymerization is described. These copolymers contain oligo(2-ethyl-2-oxazoline)acrylate (OEtOxA) and either triphenyl-4-vinylbenzylphosphonium chloride ([VBTP][Cl]) or 3-n-butyl-1-vinylimidazolium bromide ([VBuIm][Br]) ionic liquid (IL) units. The copolymers having low content of ionic poly(ionic liquid) (PIL)) segments show only lower critical solution temperature (LCST)-type phase transition with almost linear increase of their cloud points with increasing percentage of ionic PIL segments. Furthermore, LCST-type cloud points (T cL s) are found very sensitive and tunable with respect to the nature and concentration of halide ions (X − = Cl − , Br − , and I − ) and copolymer compositions. However, copolymers with high content of ionic PIL segments show both LCST-type followed by upper critical solution temperature (UCST)-type phase transitions in the presence of halide ions. Dual LCST-and UCST-type phase behaviors are prominent and repeatable for many heating/cooling cycles. Both types of cloud points are found to be sensitive to copolymer compositions, concentration, and nature and concentration of the halide ions. The phase behaviors of both types of copolymers with a very high ionic content (>90%) are exactly similar to that of P[VBTP] [Cl] or P [VBuIm][Br] homopolymers showing only UCST-type phase transition in the presence of halide ions. The inherent biocompatibility of the P(OEtOxA) segment along with the interesting dual thermoresponsiveness makes these copolymers highly suitable candidates for biomedical applications including drug delivery.

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