Double‐Stimuli‐Responsive Spherical Polymer Brushes with a Poly(ionic liquid) Core and a Thermoresponsive Shell

The synthesis of poly(ionic liquid) (PIL) nanoparticles grafted with a poly(N‐isopropyl acrylamide) (PNIPAM) brush shell is reported, which shows responsiveness to temperature and ionic strength in an aqueous solution. The PIL nanoparticles are first prepared via aqueous dispersion polymerization of a vinyl imidazolium‐based ionic liquid monomer, which is purposely designed to bear a distal atom transfer radical polymerization (ATRP) initiating group attached to the long alkyl chain via esterification reaction. The size of the PIL nanoparticles can be readily tuned from 25 to 120 nm by polymerization at different monomer concentrations. PNIPAM brushes are successfully grafted from the surface of the poly(ionic liquid) nanoparticles via ATRP. The stimuli‐responsive behavior of the poly(ionic liquid) nanoparticles grafted with PNIPAM brushes (NP‐g‐PNIPAM) in aqueous phase is studied in detail. Enhanced colloidal stability of the NP‐g‐PNIPAM brush particles at high ionic strength compared to pure PIL nanoparticles at room temperature is achieved. Above the lower critical solution temperature (LCST) of PNIPAM, the brush particles remain stable, but a decrease in hydrodynamic radius due to the collapse of the PNIPAM brush onto the PIL nanoparticle surface is observed.

     

Synthesis of polymeric ionic liquid microsphere/Pt nanoparticle hybrids for electrocatalytic oxidation of methanol and catalytic oxidation of benzyl alcohol

Herein, we present a facile approach for the synthesis of polymeric ionic liquids (PILs) microspheres for metal scavenging and catalysis. Crosslinked poly(1‐butyl‐3‐vinylimidazolium bromide) microspheres with the diameter of about 200 nm were synthesized via miniemulsion polymerization, in which 1,4‐di(vinylimidazolium) butane bisbromide was added as the crosslinker. Anion exchange of PIL microspheres with Pt precursor and followed by the reduction of Pt ions produced PIL microsphere supported Pt nanoparticle hybrids. The synthesized Pt nanoparticles with a diameter of about 2 nm are uniformly dispersed and strongly bound to the surface of PIL microspheres. The catalytic performances of PIL/Pt nanoparticle hybrids were evaluated for both the electrocatalytic oxidation of methanol and oxidation of benzyl alcohol. The PIL/Pt nanoparticle hybrids show better electrocatalytic activity towards the electrooxidation of methanol than pure Pt nanoparticles. Furthermore, they are effective and easily reusable catalysts for the selective oxidation of benzyl alcohol in aqueous reaction media, demonstrating that the synthesized PIL microspheres are suitable scaffolds for heterogeneous catalysts Pt. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Novel reversible thermoresponsive nanogel based on poly(ionic liquid)s prepared via RAFT crosslinking copolymerization

In this study, a facile strategy for the preparation of thermo‐ and pH‐responsive nanogels through reversible addition–fragmentation transfer (RAFT) crosslinking copolymerization of ionic liquid‐based monomers is demonstrated. The use of chain transfer agents (CTAs) containing carboxyl group in the RAFT polymerizations is the key to producing highly thermoresponsive nanogels. Experimental results demonstrate that the critical gelation temperature of the as‐prepared nanogels can be tuned by adjusting the feed ratio of monomer and CTA. Variable temperature Fourier transform infrared measurements and control experiments indicate that hydrogen‐bonding interactions between the carboxyl groups of CTAs are responsible for the thermoresponsive behaviors of poly(ionic liquid) (PIL)‐based nanogels. Furthermore, PIL‐based nanogels are also found to be pH‐sensitive, and can be further decorated by poly(N‐isopropylacrylamide) (PNIPAAm) via surface grafting polymerization. PNIPAAm‐grafted nanogel aqueous solutions can be reversibly transformed into macrogels upon a change in temperature. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 169–178     

Poly(3,4‐ethylenedioxythiophene) Derived from Poly(ionic liquid) for the Use as Hole‐Injecting Material in Organic Light‐Emitting Diodes

We report that poly(3,4‐ethylenedioxythiophene) derived from poly(ionic liquid) (PEDOT:PIL) constitutes a unique polymeric hole‐injecting material capable of improving device lifetime in organic light‐emitting diodes (OLEDs). Imidazolium‐based poly(ionic liquid)s were engineered to impart non‐acidic and non‐aqueous properties to PEDOT without compromising any other properties of PEDOT. A fluorescent OLED was fabricated using PEDOT:PIL as a hole‐injection layer and subjected to a performance evaluation test. In comparison with a control device using a conventional PEDOT‐based material, the device with PEDOT:PIL was found to achieve a significant improvement in terms of device lifetime. This improvement was attributed to a lower indium content in the PEDOT:PIL layer, which can be also interpreted as the effective protection characteristics of PEDOT:PIL for indium extraction from the electrodes.

     

Novel cationic polyelectrolyte coatings for capillary electrophoresis

The use of bare fused silica capillary in CE can sometimes be inconvenient due to undesirable effects including adsorption of sample or instability of the EOF. This can often be avoided by coating the inner surface of the capillary. In this work, we present and characterize two novel polyelectrolyte coatings (PECs) poly(2‐(methacryloyloxy)ethyl trimethylammonium iodide) (PMOTAI) and poly(3‐methyl‐1‐(4‐vinylbenzyl)‐imidazolium chloride) (PIL‐1) for CE. The coated capillaries were studied using a series of aqueous buffers of varying pH, ionic strength, and composition. Our results show that the investigated polyelectrolytes are usable as semi‐permanent (physically adsorbed) coatings with at least five runs stability before a short coating regeneration is necessary. Both PECs showed a considerably decreased stability at pH 11.0. The EOF was higher using Good's buffers than with sodium phosphate buffer at the same pH and ionic strength. The thickness of the PEC layers studied by quartz crystal microbalance was 0.83 and 0.52 nm for PMOTAI and PIL‐1, respectively. The hydrophobicity of the PEC layers was determined by analysis of a homologous series of alkyl benzoates and expressed as the distribution constants. Our result demonstrates that both PECs had comparable hydrophobicity, which enabled separation of compounds with log P_o/w > 2. The ability to separate cationic drugs was shown with β‐blockers, compounds often misused in doping. Both coatings were also able to separate hydrolysis products of the ionic liquid 1,5‐diazabicyclo[4.3.0]non‐5‐ene acetate at highly acidic conditions, where bare fused silica capillaries failed to accomplish the separation.     

Ion transport and relaxation in phosphonium poly(ionic liquid) homo- and co-polymers

In the present work, a poly(ionic liquid) (PIL), poly(triphenyl-4-vinylbenzylphosphonium chloride) and a series of its random copolymers with nonionic hydrophobic poly(methyl methacrylate) (PMMA) are synthesized by conventional free radical polymerization (CFRP) and reversible addition-fragmentation chain-transfer (RAFT) polymerization. The understanding of some fundamental aspects about ion transport and relaxation mechanism in PIL and PIL copolymers are investigated using dielectric spectroscopy via several theoretical models. The influence of copolymer compositions, physical blending of neat PIL and PMMA, size of counter anions (Cl⁻ and TFSI⁻) and variation of molecular weights on thermal stability, moisture sensitivity, ionic transport and relaxation properties are also studied. An enhancement of thermal stability and ionic transport property of the PIL copolymer is observed compared to those of the physically mixed blend of two homopolymers with same compositions. The incorporation of hydrophobic PMMA segment definitely decreases the moisture content in PIL copolymers than the PIL itself. In all these PIL- based systems, the temperature dependence of ionic conductivity, relaxation time and ion diffusivity are well described by Vogel-Tammann-Fulcher model. The studies of some fundamental properties of these new PIL copolymers with less moisture sensitivity may help in using them as potential polymer electrolytes in energy storage devices.     

Thin poly(ionic liquid) and poly(vinylidene fluoride) blend films with ferro‐ and piezo‐electric polar γ‐crystals

Ferro‐ and piezo‐electric poly(vinylidene fluoride) (PVDF) thin film is reported to be obtained by using a poly(ionic liquid) (PIL) [poly(2‐(dimethylamino)ethyl methacrylate) methyl chloride quaternary salt] through solution route. The short range interactions between localized cationic ions of PIL and polar >CF₂ of PVDF are responsible for modified polar γ‐PVDF (T₃GT₃Ḡ) formation. Modification in chain conformation of PVDF is confirmed by FTIR, XRD, and DSC studies suggesting the miscible PVDF–PIL (PPIL) blend. Up to 40 wt % loading of PIL in PVDF matrix enhances relative intensity of γ‐phase up to 50% in the entire crystalline phase. The P‐E hysteresis loop of PVDF‐PIL blends at 25 wt % PIL loading (PPIL‐25) thin film at sweep voltage of ±50 V shows excellent ferroelectric property with nearly saturated high remnant polarization ∼6.0 µC cm⁻² owing to large proportion of γ‐PVDF. However, non‐polar pure PVDF thin film shows unsaturated hysteresis loop with 1.4 µC cm⁻² remnant polarization. The operation voltage decreases effectively because of the polar γ‐phase formation in PPIL blended film. High‐sensitivity piezo‐response force microscopy shows electromechanical switching property at low voltages in PPIL‐25 thin films through local switching measurements, making them potentially suitable as ferroelectric tunnel barriers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 795–802     

Supramolecular assembly of poly(ionic liquid) nanogel driven by host‐stabilized charge transfer interaction

Poly(ionic liquid) (PIL)‐based nanogels, functionalized by naphthyl (Np), are fabricated via a facile one‐step ternary crosslinking copolymerization in selective solvent. The size of PIL nanogels can be conveniently regulated through the feed ratio of IL monomer to crosslinker. The presence of Np groups in PIL nanogel is confirmed by using ultraviolet–visible (UV–vis), Fourier transform infrared, and X‐ray photoelectron spectroscopy measurements. Through introducing cucurbit[8]uril (CB[8]) and bisviologen compound (DEDV) as the host molecule and electron acceptor, respectively, host‐stabilized charge transfer (HSCT) interaction is achieved through utilizing Np containing PIL nanogel as the building block. The studies reveal that PIL nanogels can form schistose aggregates in the scale of micrometer via HSCT interaction. The aggregates will be broken in the presence a competitive guest molecule (amantadine) and can recover by adding another host molecule (CB[7]). HSCT interaction among CB[8], DEDV and PIL nanogel is investigated by dynamic light scattering, UV–vis, and Proton nuclear magnetic resonance. Our studies thus provided an applicable strategy for constructing dynamic polymer nanoparticles through noncovalent interaction. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2251–2259     

Organic solvent dispersion of poly(3,4‐ethylenedioxythiophene) with the use of polymeric ionic liquid

A nonaqueous dispersion of poly(3,4‐ethylenedioxythiophene) (PEDOT) was prepared with the use of polymeric ionic liquid (PIL) as a polymerization template and phase transfer medium. A detailed investigation was performed to understand the role of PIL in the course of polymerization and phase transfer reaction. On the basis of our findings from X‐ray photoelectric spectroscopy (XPS), we propose a mechanism by which the PIL leads to the nanostructured PEDOT colloids in various organic solvents and thus facilitating smoother surface morphologies of the PEDOT‐PIL films. In addition, the enhancement of charge transport was observed for PEDOT‐PIL complex when compared with PEDOT without PIL. Raman spectroscopy indicates that there is a reduced interaction between the charge carriers on the PEDOT and the counter ions bound to PIL, thus promoting charge carrier hopping rates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6872–6879, 2008     

Highly selective GC stationary phases consisting of binary mixtures of polymeric ionic liquids

GC stationary phases composed of binary mixtures of two polymeric ionic liquids (PILs), namely, poly(1‐vinyl‐3‐hexylimidazolium) bis[(trifluoromethyl)sulfonyl]imide (poly(ViHIm‐NTf₂))/poly(1‐vinyl‐3‐hexylimidazolium) chloride (poly(ViHIm‐Cl)) and poly(1‐vinyl‐3‐hexadecylimidazolium) bis[(trifluoromethyl)sulfonyl]imide (poly(ViHDIm‐NTf₂))/poly(1‐vinyl‐3‐hexadecylimidazolium) chloride (poly(ViHDIm‐Cl)), were evaluated in terms of their on‐set bleed temperature and separation selectivity. A total of six neat or binary PIL stationary phases were characterized using the solvation parameter model to investigate the effects of the polymeric cation and anion and PIL composition on the system constants of the resulting stationary phases. The hydrogen bond basicity of the mixed poly(ViHIm‐NTf₂)/poly(ViHIm‐Cl) stationary phases was enriched linearly with the increase in the poly(ViHIm‐Cl) content. Results revealed that tuning the composition of the stationary phase allowed for fine control of the retention factors and separation selectivity for alcohols and carboxylic acids as well as selected ketones, aldehydes, and aromatic compounds. A reversal of elution order was observed for particular classes of analytes when the weight percentage of the chloride‐based PIL was increased.     

High stability silver nanoparticles–graphene/poly(ionic liquid)-based chemoresistive sensors for volatile organic compounds’ detection

Hybrids of silver nanoparticle-decorated reduced graphene oxide (Ag-RGO) have been prepared with the use of poly(ionic liquid) (PIL) as a versatile capping agent to develop volatile organic compound (VOC) sensors. The hybrid materials of Ag-RGO/PIL were assembled into three-dimensional-laminated nanostructures, where spherical Ag nanoparticles with diameters between 50 and 300 nm were homogeneously distributed on the graphene sheets and interspaced between them. Ag-RGO/PIL sensors were fabricated by spray layer-by-layer technique and used to detect a set of polar (methanol, ethanol, methyl acetate, acetone and water) and non-polar (chloroform, dichlorobenzene, toluene and styrene) organic vapours. Much higher sensitivity and discriminability were obtained for polar vapours although non-polar ones could also be detected. In comparison with either simple reduced graphene oxide or carbon nanotubes (CNT) functionalised by PIL, the hybrid Ag-RGO/PIL-based sensors showed superior performances in terms of sensitivity, selectivity, stability and high reliability. For example, a signal-to-noise ratio up to 168 was obtained for 1 ppm of methanol and signals drift between two experiments spaced out in the time of 3 months was less than 3 %. It is expected that by extrapolation, a limit of detection at the parts per billion level can be reached. These results are promising to design e-noses based on high stability chemoresistive sensors for emerging applications such as anticipated diagnostic of food degradation or diseases by the analysis of VOC, some of them being in this case considered as biomarkers.     

Preparation of main‐chain imidazolium‐functionalized amphiphilic block copolymers through combination of condensation polymerization and nitroxide‐mediated free radical polymerization and their micelle study

Main‐chain imidazolium‐functionalized amphiphilic block copolymers (PIL‐b‐PS) consisting of polyionic liquid (PIL) and polystyrene (PS) blocks have been first synthesized by condensation polymerization combined with nitroxide‐mediated free radical polymerization (NMP). The di‐functional imidazolium‐based ionic liquid (IL) having both hydroxyl and ester end groups was synthesized through Michael addition between imidazole and methylacrylate (MA) and further quaternization by 2‐chloroethanol. The HTEMPO (4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy) terminated polyionic liquid (HTEMPO‐PIL) as the hydrophilic block was prepared by condensation polymerization of di‐functional imidazolium IL and HTEMPO at a certain ratio. The hydrophobic PS block was synthesized by controlled radical polymerization of styrene using HTEMPO‐PIL through NMP, resulting PIL‐b‐PS block copolymers. The structure of block copolymers obtained has been characterized and verified by FTIR, ¹H NMR, and size exclusion chromatography analyses. In addition, the morphology and size of the micelles formed by PIL‐b‐PS block copolymers in water were investigated by transmission electron microscopy and dynamic light scattering. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Lanthanide Luminescence Improvement by Using a Functional Poly(Ionic Liquid) as Matrix and Co‐ligand

A poly(ionic liquid) (BA‐PIL) carrying a benzoic acid group in each repeating unit of the polymer architecture, which has the dual function of acting as a matrix and second ligand, has been developed. Through the incorporation of BA‐PIL with the complex [Ln(hfa)₃] (hfa=hexafluoroacetylacetone) as an emitting precursor, significant luminescence improvement was achieved in the obtained hybrid materials. Confinement of the lanthanide(III) complexes within the rigid chains of the polymer, together with replacement of the coordinated water molecules, are believed to be ascribed to the enhanced optical properties.     

Nanohybrids based on polymeric ionic liquid prepared from functionalized MWCNTs by modification of anionically synthesized poly(4‐vinylpyridine)

We report the synthesis of a composite material comprised of poly(4‐vinylpyridine) (P4VP) grafted on multiwall carbon nanotubes (MWCNTs) and the preparation of a nanohybrid via quaternization of the nitrogen atom per monomeric unit of the polymer chains. 4‐Vinylpyridine was polymerized anionically using high vacuum techniques and was reacted with MWCNTs under vacuum to be grafted on the polymer segments. The composite material was soluble in common solvents and the dispersion of the carbon nanotubes was improved after quaternization due to the formation of polymeric ionic liquid (PIL) of the MWCNTs‐g‐[P4VP‐r‐poly(4ViEtPy⁺Br^‐)] type. The successful synthesis was confirmed with Fourier‐transform infrared and Raman spectroscopies, whereas differential scanning calorimetry was adopted to verify the stability of the polymer's glass transition temperature before and after grafting on the MWCNTs. Moreover, thermogravimetric analysis was used for examining the thermal stability and the PIL formation of the composite. Energy dispersive spectroscopy measurements confirm the precipitation of silver bromide when the MWCNTs‐g‐[P4VP‐r‐poly(4ViEtPy⁺Br^‐)] is reacted with silver nitrite indicating the successful quaternization and formation of the appropriate PIL. High temperature size exclusion chromatography was used for the determination of the molecular characteristics (average molecular weight by number $\overline M _n$ , polydispersity I) of the homopolymer obtained from the filtration of the composite material. Finally, field‐emission scanning electron microscopy was used to verify the successful grafting of the polymer to the MWCNTs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Double hydrophilic diblock copolymers containing a poly(ionic liquid) segment: Controlled synthesis, solution property, and application as carbon precursor

In this contribution, we demonstrate the controlled synthesis of double hydrophilic block copolymers comprising a hydrophilic poly(ionic liquid) (PIL) segment via the RAFT/MADIX process. The non-ionic segment is made up from either poly(N-isopropylacrylamide) (PNIPAAm) or poly(N,N-dimethylacrylamide) (PDMA), due to their favorable controllable solubility in water at room temperature. They were employed as macro-chain transfer agents (macro-CTAs) for the RAFT polymerization of four different 1-vinylimidazolium ionic liquid monomers possessing different alkyl substitutes and anions. The block copolymers of PNIPAAm-b-PIL are dual stimuli-responsive copolymers that can respond to the changes in temperature and ionic strength in aqueous solution. This special property facilitated a facile anion exchange of the PIL segment. In addition, one copolymer could successfully be employed as carbon precursor for the preparation of mesoporous graphitic nanostructures in the presence of metal salts.     

Microspheres from stereocomplexes of polylactides containing ionic liquid end‐groups

Low‐molecular‐weight polymers of L ‐ and D ‐lactide containing different end‐groups (hydroxy, butoxy, trifluoromethoxy, heptafluorobutoxy, oxyethylimidazole groups, and groups derived from the imidazolium ionic liquid) are synthesized. It is shown that the nature of end‐groups affects the stereocomplexation of corresponding pairs of polymers. Stereocomplex of poly(L ‐lactide) and poly(D ‐lactide) containing imidazolium ionic liquid end‐groups (PLA‐IL) precipitates from 1,4‐dioxane solution in the form of monodisperse, perfectly spherical microspheres. Such behavior of PLA‐IL, not observed for polymers containing other end‐groups, can be attributed to the presence of strongly interacting ionic liquid end‐groups. This conclusion is supported by the results of ¹H NMR and dynamic light scattering experiments as well as by direct observation of precipitated particles by scanning electron microscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Preparation of single-walled carbon nanotube (SWNT) gel composites using poly(ionic liquids)

This paper reports a new and practical route for synthesizing nanotube-polymeric ionic liquids gel by non-covalent functionalization of oxidized single-walled carbon nanotube (SWNT) surfaces with imidazolium-based poly(ionic liquids) (PILs), using in situ radical polymerization method. A black and homogeneous precipitate SWNTs was obtained as a gel form, which is well dispersed in aqueous solution without any aggregation. The formation of SWNT gels is explained by the electrostatic attractions or π-bonds between the SWNT surface and the PIL matrix. By anion-exchange reaction of PIL bound to SWNTs, hydrophilic anions in PIL were substituted with hydrophobic anions, resulting in an effective transfer of SWNT-PIL hydrogels to organogels. The result also showed that SWNTs can effectively improve the conductivity along with the thermal stability of nanocomposite gels.     

Role of counteranions in polymeric ionic liquid-based solid-phase microextraction coatings for the selective extraction of polar compounds

A polymeric ionic liquid (PIL) poly(1-vinyl-3-hexylimidazolium chloride) (poly(ViHIm⁺Cl⁻)) was designed as a coating material for solid phase microextraction (SPME) to extract polar compounds including volatile fatty acids (VFAs) and alcohols. The extracted analytes were analyzed by using gas chromatography (GC) coupled with flame ionization detection (FID). Extraction parameters of the HS–SPME–GC–FID method, such as ionic strength, extraction temperature, pH and extraction time were optimized. Calibration studies were carried out under the optimized conditions to further evaluate the performance of the PIL-based SPME coating. For comparison purposes, the PIL poly(1-vinyl-3-hexylimidazolium bis[(trifluoromethyl)sulfonyl]imide) (poly(ViHIm⁺NTf₂⁻)) was also used as the SPME coating to extract the same analytes. The results showed that the poly(ViHIm⁺Cl⁻) PIL coating had higher selectivity towards more polar analytes due to the presence of the Cl⁻ anion which provides higher hydrogen bond basicity than the NTf₂⁻ anion. The limits of detection (LODs) determined by the designed poly(ViHIm⁺Cl⁻) PIL coating ranged from 0.02 μg L⁻¹ for octanoic acid and decanoic acid and 7.5 μg L⁻¹ for 2-nitrophenol, with precision values (as relative standard deviation) lower than 14%. The observed performance of the poly(ViHIm⁺Cl⁻) PIL coating was comparable to previously reported work in which commercial or novel materials were used as SPME coatings. The selectivity of the developed PIL coatings was also evaluated using heptane as the matrix solvent. This work demonstrates that the selectivity of PIL-based SPME coatings can be simply tuned by incorporating different counteranions to the sorbent coating.     

Crosslinking of a Single Poly(ionic liquid) by Water into Porous Supramolecular Membranes

Reversible regulation of membrane microstructures via non‐covalent interactions is of considerable interest yet remains a challenge. Herein, we discover a general one‐step approach to fabricate supramolecular porous polyelectrolyte membranes (SPPMs) from a single poly(ionic liquid) (PIL). The experimental results and theoretical simulation suggested that SPPMs were formed by a hydrogen‐bond‐induced phase separation of a PIL between its polar and apolar domains, which were linked together by water molecules. This unique feature was capable of modulating microscopic porous architectures and thus the global mechanical property of SPPMs by a rational design of the molecular structure of PILs. Such SPPMs could switch porosity upon thermal stimuli, as exemplified by dynamically adaptive transparency to thermal fluctuation. This finding provides fascinating opportunities for creating multifunctional SPPMs.