Preparation of poly(ionic liquid) composite particles and function modification with anion exchange

Abstract

Seeded dispersion polymerization of an ionic liquid monomer ([2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)amide) ([MTMA][TFSA]) was carried out in the presence of poly(methylmethacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(t-butyl methacrylate) (PtBMA) as seed particles in a methanol/water mixture. For PMMA and PEMA seed particles, composite particles with poly(ionic liquid) (PIL) were obtained. In contrast, for PtBMA seed particles, secondary nucleated PIL particles were formed and no PtBMA/PIL composite particles were obtained. These results were also predicted by theoretical consideration based on the spreading coefficients calculated from the interfacial tensions. Moreover, we showed that anion exchange of the PIL-core in the PIL/cross-liked PMMA core–shell composite particles from TFSA to Br and FeCl₄ anions can be used to modify the properties of only the core component of the composite particles.

---

Introduction

Ionic liquids which are mostly composed of organic ions are found as molten salts at room temperature^1–5 and have been the subject of research in various fields due to their low vapor pressures, high thermal stability, and non-flammability. Ionic liquids also exhibit characteristics, such as ionic conductivity and CO₂ solubility, which are expected to be useful for the development of functional materials.^6–9 The signature characteristic of ionic liquids is the ability to design their properties, such as solubility (hydrophilic/hydrophobic) or magnetic responsiveness, by changing the structure of the cations and anions.^10–15 Several researchers have reported on the preparation of solid-state materials with properties of ionic liquids.^16–20 Poly(ionic liquid)s (PILs) are polymer materials that combine the mechanical stability and processability of polymeric materials with the unique properties of ionic liquids. PILs are prepared by the polymerization of ionic liquid containing vinyl and (meth)acrylate groups on the cationic or anionic components of the liquid.^21–27 The investigation of PIL ionic conductivity by Ohno et al. was the first study to indicate that PILs have potential for use as functional materials.²⁸ Since then, many studies have been reported the functional properties of PIL in the bulk and particle states.^29–34 Sato and Tsujii prepared the concentrated PIL blushes by atom-transfer radical polymerization on the surface of silica particles and reported that the colloid crystal comprising hybrid particles exhibited a high ionic conductivity.³⁵ Other PIL studies have reported the modification of properties using anion exchange.^36–40 Khan et al. have examined monodispersed PIL microgel particles prepared by inversed suspension polymerization with a microfluidic method and used anion exchange to investigate the volume transition, pH-responsive release, magnetism, and redox ability of PIL microgel particles.⁴¹

We have previously reported the preparation of micrometer-sized monodisperse PIL particles by dispersion polymerization of [2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethanesulfonyl)amide ([MTMA][TFSA]) in methanol/ethanol with poly(vinylpyrrolidone) (PVP) as stabilizer. It was found that the obtained PIL particles dissolved in the medium by addition of LiBr due to the anion exchange exhibiting ionic liquid properties.⁴² Moreover, we prepared commodity polymer/PIL composite particles by seeded dispersion polymerization.⁴³ The composite particle was successfully prepared in the presence of poly(methyl methacrylate) (PMMA) seed particles, but the polystyrene (PS)/PIL composite particles could not be prepared. This appears to be owing to the differences in the polarity of the seed particles, which is consistent with the theoretical considerations based on the spreading coefficients calculated from the interfacial tension data. However, detailed investigation on the synthesis of composite particles was desired for enhancing the versatility.

In this study, we have investigated in detail the effect of polarity of seed polymer as well as dispersed media on the preparation of PIL composite particles by seeded (dispersion) polymerization of [MTMA][TFSA]. Moreover, property modification for the phase of polymer/PIL composite particles using anion exchange was demonstrated.

Experimental

Materials

Methyl methacrylate (MMA), ethyl methacrylate (EMA), and t-butyl methacrylate (tBMA) were purified by distillation under reduced pressure in a nitrogen atmosphere. Ethylene glycol dimethacrylate (EGDM; Nacalai Tesque Inc., Kyoto, Japan) was washed with 1 mol L⁻¹ sodium hydroxide and purified water to remove polymerization inhibitors prior to use. Reagent grade 2,2′-azobis(isobutyronitrile) (AIBN) was purified by recrystallization in methanol. 2,2′-Azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70, Wako Pure Chemical Industries, Ltd., Osaka, Japan), poly(vinylpyrrolidone) (PVP, K-30, weight-average molecular weight: 3.6 × 10⁵ g mol⁻¹), methanol and ethanol (Nacalai Tesque Inc., Kyoto, Japan), lithium bromide (LiBr) (99%, Aldrich), [2-(methacryloyloxy)ethyl]trimethylammonium chloride ([MTMA]Cl) solution (80 wt% in water, Aldrich), lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]) (99.7%, Kanto Chemical Co., Inc.), and the polyoxyethylene sorbitan monooleate (Tween 80) (Nacalai Tesque, Kyoto, Japan) emulsifier were used as received. The water used in all experiments was obtained from an Erix®UV (Millipore, Japan) purification system and exhibited a resistivity of 18.2 MΩ cm. The ionic liquid monomer (Fig. 1) was prepared by mixing the aqueous solutions of [MTMA]Cl and Li[TFSA] following the previously reported procedure.⁴² 1-Butyl-3-methylimidazolium tetrachloroferrate ([Bmim][FeCl₄]) was prepared by mixing 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) and anhydrous FeCl₃.¹¹

Fig. 1 Chemical structure of [MTMA][TFSA].

Preparation of poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(t-butyl methacrylate) (PtBMA) seed particles

Monodispersed PMMA, PEMA, and PtBMA seed particles were prepared by dispersion polymerization as follows. Preparation of PMMA and PEMA: monomer (1.2 g), PVP (0.12 g) and AIBN (0.012 g) were dissolved in methanol/water (7/3 w/w, 10.8 g). The mixtures were then poured into glass tubes and degassed using several vacuum/N₂ cycles; the sealed glass tubes were then placed in a water bath at 60 °C for 5 h with 80 cycles per min (3 cm strokes). Preparation of PtBMA: tBMA (1.2 g), PVP (0.24 g), and V-70 (0.024 g) were dissolved in methanol/water (7/3 w/w, 10.8 g). The mixtures were poured into a round-bottom Schlenk flask, sealed off with silicon rubber septum, and degassed using several N₂/vacuum cycles. The sealed flask was then placed in a water bath at 30 °C for 24 h with magnetic stirring at 200 rpm.

Seeded dispersion polymerization of the ionic liquid monomer

Seeded dispersion polymerizations of [MTMA][TFSA] (0.25 g) in the presence of PMMA, PEMA, and PtBMA seed particles (0.25 g) were performed using V-70 (2.5 mg) as the initiator in methanol/water (2.1 g/0.9 g), which is insoluble for each polymer. The polymerization was carried out in a sealed glass tube at 30 °C for 10 h under N₂ atmosphere (80 cycles per min).

Seeded polymerization of the ionic liquid monomer with PMMA seed particles in water

The homogeneous oil phase comprising [MTMA][TFSA] (0.1 g) and AIBN (1.0 mg) was ultrasonicated using ultrasonic homogenizer (NISSEI CORPORATION, US-600T, 12 mm-diameter tip, set at “Power 10”) for 5 min in Tween 80 aqueous solution (0.35 wt%, 1.0 g). The suspension was added to the dispersion [PMMA seed particles (0.1 g) and water (4.0 g)] in a round-bottom Schlenk flask, sealed off with silicon rubber septum, and degassed using several N₂/vacuum cycles. Following the absorption of [MTMA][TFSA] and AIBN for 3 h at room temperature, seeded polymerization was performed at 60 °C for 10 h.

Preparation of poly([MTMA][TFSA]) seed particles

Monodispersed poly([MTMA][TFSA]) (PIL) seed particles were prepared by dispersion polymerization as follows: starting solution of [MTMA][TFSA] (1.0 g), PVP (0.1 g), and AIBN (0.01 g) was dissolved in methanol/water (7/3 w/w, 10 g). The mixture was then poured into glass tubes and degassed using several vacuum/N₂ cycles, and the sealed glass tubes were then placed in a water bath at 70 °C for 5 h with agitation at 80 cycles per min (3 cm strokes).

Seeded dispersion copolymerization of MMA and EGDM with PIL seed particles

PIL/P(MMA-EGDM) composite particles were prepared by seeded dispersion copolymerization as follows: after MMA (0.05 g), EGDM (0.05 g), PVP (0.01 g), and V-70 (0.002 g) were dissolved in ethanol (1.0 g), the mixture was added to the dispersion [PIL seed particles (0.1 g) and ethanol (3.0 g)]. The dispersion was poured into glass tubes and degassed using several vacuum/N₂ cycles, and the sealed glass tubes were placed in a water bath at 30 °C for 24 h with agitation at 80 cycles per min (3 cm strokes). The cross-linker (EGDM) was copolymerized with MMA to prevent PMMA from dissolving in the anion exchange reaction.

Anion exchanges of PIL/P(MMA-EGDM) composite particles using LiBr and [Bmim][FeCl₄]

The ethanol dispersion of PIL/P(MMA-EGDM) composite particles [composite particles (0.05 g) and ethanol (2.0 g)] was added to the ethanol (2.0 g) that dissolved LiBr (0.2 g) or [Bmim][FeCl₄] (0.2 g). The mixture was moderately stirred at room temperature for 24 h to exchange the counter anion from TFSA with Br or FeCl₄ anions. To remove the residual salts, an as-prepared dispersion was washed by centrifugation with ethanol. The reduction reaction of Fe(III) ion in FeCl₄ anion in the system obtained after anion exchange with FeCl₄ was carried out with NaBH₄. NaBH₄ aqueous solution (1 wt%, 2.0 g) was added to 1 wt% poly([MTMA][FeCl₄])/P(MMA-EGDM) dispersion in ethanol (2.0 g) and stirred at room temperature for 12 h due to reduction of Fe(III) ion, and the as-prepared dispersion was washed by centrifugation with ethanol.

Characterization

Scanning electron microscopy (SEM; JSM-6510, JEOL, Tokyo, Japan) studies of the particles coated with platinum were performed at 20 kV. Transmission electron microscopy (TEM; JEM-1230, JEOL, Tokyo, Japan) characterization was performed at 100 kV. To observe the interior morphology of the particles, dry samples were embedded in an epoxy matrix, cured at room temperature overnight, and subsequently microtomed. The ultrathin cross sections (approximately 100 nm thick) were stained by floating on a 3 wt% aqueous phosphotungstic acid solution for 30 min at room temperature and were observed with TEM. Qualitative analyses of the products after anion exchange were conducted with a Fourier transform infrared spectrometer (FT-IR; FT/IR-6200, JASCO, Tokyo, Japan) using a pressed KBr pellet technique. To determine the interfacial tensions, contact angle measurements were carried out with a DropMaster 300 (Kyowa Interface Science, Saitama, Japan) instrument at room temperature.

Results and discussion

Effect of seed particles and medium on seeded dispersion polymerization of [MTMA][TFSA]

In our previous study of the preparation of PMMA/PIL composite particles, we have found that PIL composite particle formation was affected by the polarity of seed particles.⁴³ It was also found that the spreading coefficient (S, mN m⁻¹) is useful for the understanding of the thermodynamics of particle formation and the understanding and prediction of the particle morphology.⁴³ In this study, we use three kinds of methacrylate seed particles to investigate the effects of seed particles polarity in detail. Since the spreading coefficient is defined as S_i = γ_jk − (γ_ij + γ_ik) where γ_jk, γ_ij, and γ_ik are interfacial tensions between each component, we first examined the surface tension properties of the three systems.

The polar components of surface tension (γ_p, mN m⁻¹) of PMMA, PEMA, and PtBMA were calculated to be 8.5, 3.0, and 2.6 mN m⁻¹, respectively by contact angle measurements with CH₂I₂ and water. Since the unique interactions between the surface of the PIL film and water can lead to inaccurate surface tension values,⁴⁴ the surface tension of PIL was measured by contact angle measurement using hexadecane and CH₂I₂. Using the Young–Owens equation, the γ_d (dispersive component of surface tension) and γ_p values were calculated to be 25.6 and 10.6 mN m⁻¹, respectively. The surface tensions for each component are summarized in Table 1. Using these surface tension data, the S values were calculated for each system and are presented in Table 2.

Table 1 Dispersive (γ^d), polar (γ^p), and total (γ) components of the surface tension (mN m⁻¹) at 298 K

	γ^d	γ^p	γ
PMMA	40.4	8.5	48.9
PEMA	35.2	3.0	38.2
PtBMA	33.9	2.6	36.5
Poly([MTMA][TFSA])	25.6	10.6	36.2
Methanol^45	18.2	4.3	22.5

---

Table 2 Spreading coefficients for each system

Seed polymer	Spreading coefficient^a
	Sseed	SPIL	Ssolvent
a Si ≥ 0: spread (wetting); Si < 0: not spread.
PMMA	−6.6	−0.5	−3.6
PEMA	−6.6	−4.9	0.8
PtBMA	−6.6	−5.4	1.3

---

The obtained S values enable us to predict the likelihood of composite particle formation. The relation between morphology and each S value is as follows:⁴⁶ (i) when S_seed < 0, S_PIL ≥ 0, and S_solvent < 0 are satisfied, the morphology of the particles after polymerization is “core–shell”. (ii) When S_seed < 0, S_PIL < 0, and S_solvent < 0 are satisfied, the morphology of particles after polymerization is “partial engulfing”. (iii) When S_seed < 0, S_PIL < 0, and S_solvent ≥ 0 are satisfied, the morphology of particles after polymerization is “individual” (Scheme 1). In the case of PMMA seed particles, these relations suggest that it should be possible to obtain composite particles by seeded dispersion polymerization. In contrast, for the PEMA and PtBMA seed particles, the obtained positive S values suggest that synthesis of composite particles would be difficult.

Scheme 1 Thermodynamically favorable morphologies of composite particles predicted using spreading coefficients.

To confirm the accuracy of the morphological prediction of composite particles based on the spreading coefficient, seeded dispersion polymerizations of [MTMA][TFSA] using PMMA, PEMA, and PtBMA seed particles were carried out. Seeded dispersion polymerization with PMMA seed particles resulted in particles with larger diameters than that of PMMA seed particles obtained while maintaining monodispersity (Fig. 2a–a′′). The particles exhibit a sea-island structure composed of PIL domains in PMMA matrix because the PIL phase was stained with phosphotungstic acid. On the contrary, in the case of PtBMA seed particles, the obtained particles were observed to possess a raspberry-like morphology. However, those particles were not PtBMA/PIL composite particles but a mixture of micron-sized PtBMA particles and nano-sized PIL particles indicating that individual morphology was observed in the PtBMA system (Fig. 2c–c′′). The raspberry-like particles should be formed by adsorption of nano-sized PIL particles on micron-sized PtBMA particles during the drying process. The nano-sized particles as well as micron-sized particles were detected with dynamic light scattering analysis before dying. That morphology was also observed in previous report,⁴³ wherein similar morphology was obtained by the drying process after seeded dispersion polymerization of styrene using PIL seed particles. These results are consistent with the spreading coefficient based predictions. Although the morphology of particles obtained after seeded dispersion polymerization with PEMA seed particles was predicted to be “individual”; in fact, the formation of composite particles (Fig. 2b–b′′) were observed using the PEMA seed particles. This result may be due to the fact that in this case, the S_solvent value is close to zero as well as to the swelling of the PEMA seed particles with [MTMA][TFSA] in the initial stage of polymerization; such swelling decreases the interfacial tension between the seed particle and the PIL possibly leading to a shift of S_solvent to a negative value.

Fig. 2 (a–c) SEM images of PMMA, PEMA, and PtBMA seed particles and (a′–c′) particles obtained after seeded dispersion polymerization of [MTMA][TFSA]. (a′′ and b′′) TEM image of ultrathin cross sections of obtained particles stained for 30 min with a 3 wt% aqueous phosphotungstic acid solution.

Next, preparation of PMMA/PIL composite particles in water was carried out to investigate the effects of the dispersed medium polarity. Here, the polymerization condition was changed to seeded polymerization because [MTMA][TFSA] is insoluble in water. The spreading coefficients in this system were changed by the change the medium as follows: S_PMMA = −9.0 < 0, S_PIL = +1.9 > 0, and S_water = −32.4 < 0. Based on these values, it is expected that it will be possible to obtain core–shell PMMA/PIL composite particles in a batch system. As shown in Fig. 3a and b, no secondly nucleated particles were observed and the diameter of the obtained particles after seeded polymerization in water was larger than that of PMMA seed particles that maintain monodispersity. The interior structure was observed to be a core–shell structure composed of light PMMA cores surrounded by dark PIL shells (Fig. 3c), whose results are also consistent with the expected morphology from the spreading coefficient. In the seeded polymerization, most of the monomer should exist in the seed particles before polymerization, wherein the viscosity becomes lower than that of the seeded dispersion polymerization system resulting in the formation of thermodynamically stable morphology.

Fig. 3 (a) SEM images of PMMA seed particles and (b) particles prepared by seeded polymerization of [MTMA][TFSA] in water. (c) TEM photograph of ultrathin cross sections of PMMA/poly([MTMA][TFSA]) composite particles stained for 30 min with a 3 wt% aqueous phosphotungstic acid solution.

Property modification of PIL composite particles utilizing anion exchange

In a previous study, we have reported that the PIL particles exhibited ionic liquid properties: they could be observed by SEM without platinum coating and the solubility of the PIL particles could be easily changed by changing the counter anion.⁴² Therefore, anion exchange of the core–shell PMMA/PIL composite particles was carried out in this study in order to modify the properties of only the PIL component of the composite particles. When anion exchange of [TFSA]⁻ of the PIL particles with the hydrophilic anion such as Br⁻ and FeCl₄⁻ was carried out, PIL particles were dissolved in the medium because the behavior of PIL was changed from hydrophobic to hydrophilic by anion exchange. To prevent the PIL component of the composite particles from dissolving after anion exchange, the preparation of PIL composite particles with a core–shell structure composed of PIL core cross-linked shell was carried out by seeded dispersion polymerization. When seeded dispersion polymerization of MMA and EGDM with PIL seed particles was carried out, the composite particles composed of PIL core and P(MMA-EGDM) shell were successfully prepared (Fig. 4).

Fig. 4 (a) SEM images of PIL seed particles and (b) particles prepared by seeded dispersion copolymerization of MMA and EGDM. (c) TEM image of ultrathin cross-sections of the obtained particles stained for 30 min with 3 wt% aqueous phosphotungstic acid solution.

Using PIL/P(MMA-EGDM) composite particles, the anion exchange was carried out by the addition of LiBr ethanol solution to the dispersion of the composite particles. Fig. 5a shows the SEM image of PIL/P(MMA-EGDM) composite particles after anion exchange using LiBr ethanol solution at room temperature for 24 h. While most of the obtained particles have maintained their original spherical shapes, some composite particles exhibit dents after the anion exchange. It is likely that the elution of PIL-core (poly([MTMA]Br) can be soluble in ethanol) into ethanol media leads to the presence of dents in the P(MMA-EGDM)-shell. Anion exchange of the composite particles was confirmed by the FT-IR (bottom of Fig. 5) as shown by the absence of the peaks at 1355 cm⁻¹ attributed to the S(=O)₂ of TFSA anion in the spectra of the obtained particles, indicating that the TFSA anion was replaced with Br-anion and the PIL core was dissolved in ethanol. When ultrathin cross-sections of PIL[Br]/P(MMA-EGDM) particles were observed with TEM, PIL[Br] cores were absent and only P(MMA-EGDM) shells were observed (Fig. 5b). This suggested that the PIL[Br] core should be dissolved in water during the microtomed process, wherein the ultrathin cross-sections were floated on the water after cutting. This result also indicated that the anion exchange reaction was successfully carried out for the PIL/P(MMA-EGDM) composite particles.

Fig. 5 (Top) (a) SEM image of PIL[Br]/P(MMA-EGDM) composite particles and (b) TEM image of ultrathin cross sections of the particles. (Bottom) (a) FT-IR spectra of PIL/P(MMA-EGDM) composite particles before and (b) after anion exchange procedure with LiBr.

To modify the magnetic properties of the composite particles, anion exchange reaction was carried out using [Bmim][FeCl₄]. As shown in Fig. 6a, the morphology of obtained particles after anion exchange reaction did not show any differences with the morphologies observed for the composite particles prior to the anion exchange. The anion exchange of the [TFSA] anion with the FeCl₄ anion was also confirmed by FT-IR. The outside morphology of the particles obtained after reductive reaction maintained its initial state and Fe nanoparticles were observed inside the particles (Fig. 6b and c). As shown in Fig. 6d, the obtained particles exhibited magnetic responsiveness, demonstrating that magnetic PIL composite particles were successfully prepared using the anion exchange reaction.

Fig. 6 SEM images of (a) PIL/P(MMA-EGDM) composite particles after anion exchange procedure with [Bmim][FeCl₄] and (b) after the reduction reaction of PIL[FeCl₄]/P(MMA-EGDM) particles with NaBH₄. (c) TEM photograph of ultrathin cross-sections of the particles and (d) visual appearance of the particles responding to a neodymium magnet.

Conclusions

Seeded dispersion polymerization of ionic liquid monomer [MTMA][TFSA] in methanol/water mixtures with PMMA and PEMA seed particles led to the formation of polymer/PIL composite particles. On the contrary, in the case of PtBMA seed particles, the secondary nucleation of the PIL particles was occurred and no composite particles were obtained. We also successfully prepared core–shell PMMA/PIL composite particles with a PMMA core and a PIL shell by seeded polymerization in water media. These results suggested that the polarity of seed polymer and solvent influence the formation of PIL composite particles. Moreover, we demonstrated that anion exchange can be used to introduce a functional property, such as magnetism, into the PIL/P(MMA-EGDM) core–shell composite particles prepared by seeded dispersion copolymerization of MMA and EGDM in ethanol using the PIL seed particles.

Acknowledgements

This work was partially supported by a Grant-in-Aid for Scientific Research (Grant No. 26288103) from the Japan Society for the Promotion of Science (JSPS) and by a Research Fellowship of JSPS for Young Scientists (given to M. T.).

References

1. T. Welton, Chem. Rev., 1999, 99, 2071–2083.
2. R. Sheldon, Chem. Commun., 2001, 2399–2407.
3. J. Ryan, F. Aldabbagh, P. B. Zetterlund and B. Yamada, Macromol. Rapid Commun., 2004, 25, 930–934.
4. P. Kubisa, J. Polym. Sci., Part A: Polym. Chem., 2005, 43, 4675–4683.
5. J. P. Hallett and T. Welton, Chem. Rev., 2011, 111, 3508–3576.
6. L. A. Blanchard, D. Hancu, E. J. Beckman and J. F. Brennecke, Nature, 1999, 399, 28–29.
7. M. Galinski, A. Lewandowski and I. Stepniak, Electrochim. Acta, 2006, 51, 5567–5580.
8. N. V. Plechkova and K. R. Seddon, Chem. Soc. Rev., 2008, 37, 123–150.
9. Z. G. Lei, C. N. Dai and B. H. Chen, Chem. Rev., 2014, 114, 1289–1326.
10. C. M. Gordon, J. D. Holbrey, A. R. Kennedy and K. R. Seddon, J. Mater. Chem., 1998, 8, 2627–2636.
11. S. Hayashi and H. Hamaguchi, Chem. Lett., 2004, 33, 1590–1591.
12. C. Chiappe and D. Pieraccini, J. Phys. Org. Chem., 2005, 18, 275–297.
13. H. Ohno, Bull. Chem. Soc. Jpn., 2006, 79, 1665–1680.
14. C. Hardacre, J. D. Holbrey, M. Nieuwenhuyzen and T. G. A. Youngs, Acc. Chem. Res., 2007, 40, 1146–1155.
15. H. M. Marwani, Cent. Eur. J. Chem., 2010, 8, 946–952.
16. J. Fuller, A. C. Breda and R. T. Carlin, J. Electrochem. Soc., 1997, 144, L67–L70.
17. M. A. Susan, T. Kaneko, A. Noda and M. Watanabe, J. Am. Chem. Soc., 2005, 127, 4976–4983.
18. B. Yu, F. Zhou, C. W. Wang and W. M. Liu, Eur. Polym. J., 2007, 43, 2699–2707.
19. K. Matsumoto, B. Talukdar and T. Endo, Polym. Bull., 2011, 66, 779–784.
20. H. Minami, H. Fukaumi, M. Okubo and T. Suzuki, Colloid Polym. Sci., 2013, 291, 45–51.
21. J. C. Salamone, S. C. Israel, P. Taylor and B. Snider, Polymer, 1973, 14, 639–644.
22. J. B. Tang, H. D. Tang, W. L. Sun, H. Plancher, M. Radosz and Y. Q. Shen, Chem. Commun., 2005, 3325–3327.
23. O. Green, S. Grubjesic, S. W. Lee and M. A. Firestone, Polym. Rev., 2009, 49, 339–360.
24. D. Mecerreyes, Prog. Polym. Sci., 2011, 36, 1629–1648.
25. A. S. Shaplov, E. I. Lozinskaya, D. O. Ponkratov, I. A. Malyshkina, F. Vidal, P. H. Aubert, O. V. Okatova, G. M. Pavlov, L. I. Komarova, C. Wandrey and Y. S. Vygodskii, Electrochim. Acta, 2011, 57, 74–90.
26. J. Y. Yuan, D. Mecerreyes and M. Antonietti, Prog. Polym. Sci., 2013, 38, 1009–1036.
27. T. P. Fellinger, A. Thomas, J. Y. Yuan and M. Antonietti, Adv. Mater., 2013, 25, 5838–5854.
28. H. Ohno and K. Ito, Chem. Lett., 1998, 751–752.
29. M. J. Muldoon and C. M. Gordon, J. Polym. Sci., Part A: Polym. Chem., 2004, 42, 3865–3869.
30. R. Marcilla, M. Sanchez-Paniagua, B. Lopez-Ruiz, E. Lopez-Cabarcos, E. Ochoteco, H. Grande and D. Mecerreyes, J. Polym. Sci., Part A: Polym. Chem., 2006, 44, 3958–3965.
31. J. Y. Yuan and M. Antonietti, Macromolecules, 2011, 44, 744–750.
32. M. Koebe, M. Drechsler, J. Weber and J. Y. Yuan, Macromol. Rapid Commun., 2012, 33, 646–651.
33. N. Rozik, M. Antonietti, J. Y. Yuan and K. Tauer, Macromol. Rapid Commun., 2013, 34, 665–671.
34. Y. Men, D. Kuzmicz and J. Y. Yuan, Curr. Opin. Colloid Interface Sci., 2014, 19, 76–83.
35. T. Sato, T. Morinaga, S. Marukane, T. Narutomi, T. Igarashi, Y. Kawano, K. J. Ohno, T. Fukuda and Y. Tsujii, Adv. Mater., 2011, 23, 4868–4872.
36. O. Azzaroni, A. A. Brown and W. T. S. Huck, Adv. Mater., 2007, 19, 151–154.
37. M. Dobbelin, R. Tena-Zaera, R. Marcilla, J. Iturri, S. Moya, J. A. Pomposo and D. Mecerreyes, Adv. Funct. Mater., 2009, 19, 3326–3333.
38. M. Dobbelin, V. Jovanovski, I. Llarena, L. J. C. Marfil, G. Cabanero, J. Rodriguez and D. Mecerreyes, Polym. Chem., 2011, 2, 1275–1278.
39. N. Sahiner, S. Demir and S. Yildiz, Colloids Surf., A, 2014, 449, 87–95.
40. C. X. Lin, W. Zhu, H. W. Yang, Q. An, C. A. Tao, W. N. Li, J. C. Cui, Z. L. Li and G. T. Li, Angew. Chem., Int. Ed., 2011, 50, 4947–4951.
41. M. T. Rahman, Z. Barikbin, A. Z. M. Badruddoza, P. S. Doyle and S. A. Khan, Langmuir, 2013, 29, 9535–9543.
42. M. Tokuda, H. Minami, Y. Mizuta and T. Yamagami, Macromol. Rapid Commun., 2012, 33, 1130–1134.
43. M. Tokuda, T. Shindo and H. Minami, Langmuir, 2013, 29, 11284–11289.
44. M. Tokuda, T. Sanada, T. Shindo, T. Suzuki and H. Minami, Langmuir, 2014, 30, 3406–3412.
45. C. J. Van Oss, Interfacial Forces in Aqueous Media, CRC Press/Taylor & Francis, Boca Raton, FL, 2nd edn, 2006.
46. S. Torza and S. G. Mason, J. Colloid Interface Sci., 1970, 33, 67.

---