Hydrogen-Bonding-Mediated Fragmentation and Reversible Self

Article pubs.acs.org/Macromolecules

Hydrogen-Bonding-Mediated Fragmentation and Reversible Selfassembly of Crystalline Micelles of Block Copolymer Jie-Xin Yang, Bin Fan, Jun-Huan Li, Jun-Ting Xu,* Bin-Yang Du,* and Zhi-Qiang Fan MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China S Supporting Information *

ABSTRACT: Two hydrogen (H)-bond donors, phenol and Lthreonine, were added into the aqueous solutions containing crystalline micelles of a poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) block copolymer, respectively. Dynamic light scattering (DLS) characterization showed that the micellar size became smaller after addition of phenol. Transmission electron microscopy (TEM) results revealed that the long crystalline cylindrical micelles formed in the neat aqueous solution were fragmented into short cylinders and even quasispherical micelles, as the phenol concentration increased. By contrast, the spherical PCL-b-PEO crystalline micelles could be transformed into short cylinders and then long cylinders after addition of L-threonine. Reversible morphological transformation was realized for the PCL-b-PEO crystalline micelles by adding these two H-bond donors alternately. It is confirmed that both phenol and L-threonine could form H-bonds with PEO. We proposed that, the micellar corona was swollen by phenol, leading to fragmentation of the micellar core, whereas the PEO blocks in the micellar corona was dynamically cross-linked by L-threonine beacuse of its multiple H-bond-donation groups, resulting in a smaller reduced tethering density. the different soluble blocks existed on the two crystal surfaces.38 Therefore, a question is raised: Can pre-existing crystalline core of BCP micelles be fragmented when a strong stress is introduced into the micellar corona? It has been reported that hydrogen (H)-bonding complexation may alter the aggregated structures of amorphous micelles of BCPs. For example, poly(acrylic acid) (PAA) was frequently added into the solutions of poly(ethylene oxide) (PEO)- or poly(4-vinylpyridine) (P4VP)-containing BCPs and the assembly behavior of the BCP/PAA complexes varied with the ratio of PEO/PAA or P4VP/PAA.39−48 Small organic molecules, such as phenol, salicylic acid and other H-bond donors, could also induce morphological transformation of the PEO-containing BCP micelles in aqueous solution.49−52 In the present work, we added phenol and L-threonine, respectively, into the aqueous solutions of a poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymer (PCL59-b-PEO113), which formed crystalline cylindrical micelles in water. We tried to swell the micellar corona and produce stress in the corona, which may be transferred to the crystalline micellar core and further fragment it.

1. INTRODUCTION Recently, crystallization-driven self-assembly (CDSA) of block copolymers (BCPs) to form crystalline micelles has drawn much attention of researchers.1−3 Crystallization endows selfassembly of BCPs with some unique characteristics, including easy control of micellar morphology,4−19 living growth,20−24 and ability to construct “block co-micelles” and micelles with a complicated structure.25−34 Nevertheless, due to the strong vitrification effect of crystallization, CDSA of BCPs is usually one-way and irreversible, unless intensive external stimulus, such as sonication or heating to melt the core, is exerted.35,36 This means that, once the crystalline micelles of BCPs are formed, they can hardly degenerate or change their morphologies when external environment is altered. By contrast, the morphological transformation of amorphous BCP micelles may be reversible when the micelles are in thermodynamic equilibrium.37 Bidirectional self-assembly can lead to flexible application of crystalline micelles so that they can change their morphologies and functions on demand. In order to realize reversible morphological transformation of crystalline micelles, uniform fragmentation of the crystalline core is key, which has not been achieved under a mild condition so far. Cheng et al. found that, scrolled single crystals could be obtained for the triblock copolymer of polystyrene-b-poly(ethylene oxide)-b-poly(1-butene oxide) with a crystalline midblock when the unbalanced surface stresses induced by © XXXX American Chemical Society

Received: October 28, 2015 Revised: December 9, 2015

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2. EXPERIMENTAL SECTION

trations. It is found that the micellar size decreases gradually as the phenol concentration increases, and then becomes nearly constant when the phenol concentration is beyond 0.15 mol/L. Transmission electron microscopy (TEM) characterization reveals that PCL59-b-PEO113 forms mixed micelles of spheres, short and long cylinders in the neat aqueous solution (Figure 2a). At the phenol concentrations of 0.05 and 0.13 mol/L, the

Materials. The block copolymer PCL59-b-PEO113 (the subscripts being the polymerization degrees of the blocks) with a narrow molecular weight distribution (Mw/Mn = 1.09) was synthesized according to our previous work.53 The number-average molecular weights of the PEO and PCL blocks were calculated from 1H NMR spectrum and the molecular weight distribution was determined by gel permeation chromatography (GPC). Analytical grade organic reagents, tetrahydrofuran (THF), phenol and L-threonine were purchased from J&K Scientific and used as received. Preparation of the Micellar Solutions. PCL59-b-PEO113 was first dissolved in THF to give a concentration of 1 mg/mL. Afterward, 10 mL of PCL59-b-PEO113 THF solution was transferred into a dialysis bag (molecular-weight cutoff =3500 g/mol), which was dialyzed against twice-distilled water at room temperature to remove THF. After dialysis, the micellar solution was transferred into a volumetric flask. A certain volume of deionized water was used to wash the dialysis bag and added to the flask. The final solution volume was fixed at 100.0 mL and the concentration of the micellar solution was 0.1 mg/mL. Characterizations. Dynamic light scattering (DLS) measurements were performed on a Brookhaven Instrument BI-200SM with a laser wavelength of 636 nm at 25 °C. The scattering angle was fixed at 90°. The DLS data were analyzed with the software supplied by Brookhaven and the apparent hydrodynamic diameters of the micelles were obtained. Transmission electron microscopy (TEM) observations were carried out on a JEOL JEM-1230 electron microscope at an acceleration voltage of 80 kV. TEM samples were prepared by first dropping 4 μL of the micellar solution onto carbon-coated copper grids, which was then negatively stained with phosphotungstic acid (PTA) aqueous solution. The stained TEM samples were frozen by liquid nitrogen and freeze-dried under vacuum at −20 °C to avoid the reassembly and aggregation of the micelles during the drying process. Because of negative staining, the bright area in the obtained TEM images corresponds to the crystalline core of the PCL-b-PEO micelles. The DSC experiments were performed on a TA Q200 instrument. Freeze-dried micelles were used for the DSC experiments and the heating rate was 10 °C/min. The UV−vis spectra were recorded on a Cary 100 spectrometer. Fourier-transform infrared (FT-IR) spectra were recorded on a Thermo Fisher Scientific LLC Nicolet 6700 spectrometer. OPUS spectroscopic software was used for data analysis. Deconvolution of the FT-IR bands was performed by using OriginLab Origin software.

Figure 2. TEM images of PCL59-b-PEO113 micelles in the aqueous solutions with different phenol concentrations: (a) 0 mol/L; (b) 0.05 mol/L; (c) 0.13 mol/L; (d) 0.4 mol/L.

long cylindrical micelles disappear and only short cylinders and spheres are observed (Figure 2, parts b and c). The length of the short cylindrical micelles decreases with increasing the phenol concentration. When the phenol concentration reaches 0.4 mol/L, the micelles become spherical-like and no cylinders are observed (Figure 2d). It should be noted that the crystalline micellar cores are still anisotropic in spite of the overall spherical shape. The TEM and DLS results show that phenol undoubtedly can fragment the crystalline cylindrical micelles of PCL-b-PEO BCPs into short cylindrical or even quasi-spherical ones. Decrease of the micelle size after addition of phenol is also observed for other two PCL-b-PEO BCPs (PCL46-b-PEO44 and PCL73-b-PEO44), as shown in Figure S1 of the Supporting Information, indicating that fragmentation of the PCL-b-PEO crystalline micelles by phenol is not a single case. We investigated the change of the micellar size with time after addition of phenol (Figure S2 in the Supporting Information). It is found that the micellar size decreases quickly, showing that fragmentation of the crystalline cylindrical micelles can be completed in a short period. The above results show that phenol can interact with the PEO chains, which may cause swelling of the micellar corona and fragmentation of the micellar core. The UV−vis spectra of the neat PEO, phenol and their mixture in aqueous solutions are shown in Figure S3. It can be seen that the absorption band of PEO around 240 nm disappears after addition of phenol, which verifies the interaction between PEO and phenol.54,55 The H-bonding interactions between phenol and PEO are

3. RESULTS AND DISCUSSION Effect of Phenol. We first added different amounts of phenol into the aqueous solution of PCL59-b-PEO113 micelles with a concentration of 0.1 mg/mL. Figure 1 shows the apparent hydrodynamic diameters of the micelles measured by dynamic light scattering (DLS) at various phenol concen-

Figure 1. Variation of the apparent hydrodynamic diameter of PCL59b-PEO113 micelles with phenol concentration in the aqueous solution. B

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Macromolecules further confirmed by FT-IR, as shown in Figure S4 and Table S1 of the Supporting Information. The intensity of IR band corresponding to the H-bonded C−O−C at 1060 cm−1 becomes evidently stronger after mixing with phenol. Figure 3 shows the DSC melting curves of freeze-dried PCL59-b-PEO113 micelles and micelles/phenol mixture. It

Figure 4. Distributions of the apparent hydrodynamic diameter obtained by DLS for PEO (Mn = 5000) in the neat aqueous solution and in the solution containing 0.15 mol/L phenol.

micellar size of PCL59-b-PEO113 increases gradually with time after addition of L-threonine, as revealed by the DLS measurements (Figure 5). This result shows that the effect of

Figure 3. DSC melting curves of freeze-dried micelles prepared from the neat PCL59-b-PEO113 solution and the solution containing 0.4 mol/L phenol. The heating rate is 10.0 °C/min.

should be pointed out that the PEO chains in the micelle corona can also crystallize after being dried. For the neat PCL59-b-PEO113 micelles, the melting peaks of PEO and PCL are overlapped, and the melting peak of PEO appears as a shoulder at lower temperature. Three melting peaks are observed for the mixture of PCL59-b-PEO113 micelles with phenol, which correspond to melting of phenol (37.7 °C), PEO (45.6 °C) and PCL (54.5 °C), respectively. By comparing the DSC melting curves of the freeze-dried PCL59-b-PEO113 micelles with and without phenol, it can be seen that the addition of phenol suppresses the melting temperature (Tm) of PEO block but enhances the Tm of PCL block. This result indicates that phenol interacts only with the PEO block but does not interact with the PCL block, although there are carbonyl groups in the PCL chains. On the one hand, the interaction between the PEO block and phenol will hinder crystallization of the PEO block, leading to a lower Tm of PEO. On the other hand, the adverse effect of the PEO block on crystallization of the PCL block may be weakened due to the lowered crystallizability of PEO, leading to the increase in Tm of PCL.53 Figure 4 shows the distributions of the apparent hydrodynamic diameter of PEO (Mn = 5000) in the neat aqueous solution and in the aqueous solution containing 0.15 mol/L phenol, as measured by DLS. It is obseved that PEO coil size becomes larger after addition of phenol. This observation confirms the swelling of the PEO coil induced by phenol, which may result from the H-bonding interaction between the PEO block and phenol. On the basis of these findings, we speculate that the stress causing the expansion of the PEO corona can be transferred to the micellar core and such a stress is large enough to fragment the crystalline micellar core. To our best knowledge, this is the first report that the crystalline micelles of BCPs can be fragmented under a mild condition, which provides a basis for reversible morphological transformation of crystalline assemblies of BCPs. Effect of L-Threonine. L-Threonine was added into the PCL-b-PEO micellar solution as well. It is surprising that the

Figure 5. Variation of the apparent hydrodynamic diameter of PCL59b-PEO113 micelles in the aqueous solution with time after addition of L-threonine. The concentration of L-threonine is 0.49 mol/L. L-threonine

is opposed to that of phenol. In order to reveal the effect of L-threonine more clearly, we filtered the micellar solution to remove the cylindrical micelles (Figure 6a). Note that PCL59-b-PEO113 forms mixed spherical and cylindrical micelles in aqueous solution (cf. Figure 2a). L-Threonine was then added into the solution containing only spherical PCL59-bPEO113 micelles. It is found that mixture of spherical and shortrod-like micelles are formed after 1.5 days of adding L-threonine (Figure 6b), which indicates that parts of spherical micelles are transformed into short rods in the presence of L-threonine. After 3 days of adding L-threonine, the spherical micelles disappear and only rod-like micelles are observed (Figure 6c), suggesting that all the spherical micelles are transformed into rod-like ones. With further prolongation of time, long cylindrical micelles and even some lamellar micelles are formed (Figure 6d). As a result, L-threonine can induce sphere-tocylinder and even sphere-to-lamella transitions of the PCL59-bPEO113 crystalline micelles, which agrees with the increase of the micellar size revealed by DLS (cf. Figure 5). It can be also seen from Figure 5 that the micellar size changes in several days, which indicates that the morphological transformation of the micelles proceeds more slowly as compared with the fragmentation process. This phenomenon is in accordance with C

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Figure 7. Variations of the apparent hydrodynamic diameter of PCL59b-PEO113 micelles with time in the aqueous solutions containing 0.49 mol/L L-threonine at different pH values. The isoelectric point of Lthreonine is 6.16.

Nevertheless, the H-bonding interaction may be weakened when the pH value is above the isoelectric point, at which Lthreonine carries negative charges. Reversible Morphological Transformation of the Crystalline Micelles. Since phenol and L-threonine have opposite effects on the morphology of PCL-b-PEO crystalline micelles, it is expected that reversible morphological transformation may be realized by addition of these two compounds, respectively. We start from the cylindrical micelles prepared from the PCL59-b-PEO113 micellar solution containing 0.49 mol/L L-threonine (Figure 8a). After dialysis of L-threonine,

Figure 6. TEM images of PCL59-b-PEO113 micelles in the aqueous solution after filtration with a 0.45 mm Millipore PVDF membrane (a) and after 1.5 (b), 3, (c) and 4 days (d) of adding L-threonine. The concentration of L-threonine is 0.49 mol/L.

our previous result because the sphere-to-cylinder transition may proceed via an end-to-end coupling mechanism.23 The effect of L-threonine concentration on the micellar size of PCL59-b-PEO113 was studied as well. It is observed that a critical L-threonine concentration is required to trigger the morphological transformation of PCL59-b-PEO113 micelles, which is about 0.29 mol/L at pH = 7 (Figure S5 in Supporting Information). As shown in Figure S6 of the Supporting Information, Lthreonine contains both hydroxyl and amino groups so that Hbonding interaction may also occur between PEO and Lthreonine. The FT-IR spectrum shows that the band for the Hbonded C−O−C in the PEO/L-threonine mixture is stronger than that in the neat PEO (Figure S4 in the Supporting Information). Quantitative analysis of the FT-IR result shows that both the area ratio and height ratio of the IR bands for Hbonded and free C−O−C in the PEO/phenol and PEO/Lthreonine mixtures are larger than those in the neat PEO (Table S1 in Supporting Information), indicating that Lthreonine also takes effect via H-bonding interaction with PEO, which is similar to phenol. Since the amino and carboxyl groups in L-threonine can be ionized at different pH values, the H-bonding interaction between L-threonine and PEO may change with the pH value of the micellar solution. Therefore, we studied the PCL-b-PEO micellar size in the aqueous solutions with different pH values in the presence of 0.49 mol/L L-threonine. As shown in Figure 7, when the pH value is 5.16, which is lower than the isoelectric point of L-threonine (pH = 6.16), the micellar size increases more rapidly. By contrast, there is no evident change in micellar size at the pH value (pH = 7.17) larger than its isoelectric point. These results indicate that the effect of L-threonine on the size of PCL-b-PEO micelles is pH-dependent. At a low pH value, L-threonine carries positive charges and the H-bonding interaction between L-threonine and PEO is strengthened.

Figure 8. TEM images of PCL59-b-PEO113 micelles in the reversible cycle experiment: (a) cylindrical micelles in the neat aqueous solution prepared by addition of L-threonine followed by dialysis; (b) spherical micelles after addition of phenol (0.15 mol/L); (c) cylindrical micelles after addition of L-threonine (0.49 mol/L) at the second time.

phenol (0.15 mol/L) is added into the solution. As shown in Figure 8b, the micelles become spherical. Subsequently, phenol is dialyzed and 0.49 mol/L L-threonine is added again, the cylindrical micelles are recovered after 6 days (Figure 8c). These results suggest that we can readily switch the morphology of PCL 59 -b-PEO 113 crystalline micelles by alternately adding different H-bond donors. Possible Mechanism. The opposite effects of phenol and L-threonine may originate from the different number of Hbond-donating group in these two compounds. There is only one H-bond-donating group (hydroxyl) in a single phenol molecule. The H-bonding interaction between phenol and PEO leads to the enrichment of phenol in the micellar corona and swelling of the corona, which may further cause stress inside the corona. The stress can be transferred to the micellar core due to the chemical linkage between the corona- and core-forming blocks. The magnitude of the stress in the micellar corona increases with the phenol concentration. Moreover, the stress is smaller at the ends of the cylindrical micelles because of extra D

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Macromolecules lateral surfaces, as compared in the middle part of the cylindrical micelles. Therefore, the stress can be released by fragmenting the long cylindrical micelles in order to produce more lateral surfaces. The larger the stress, the more lateral surfaces are produced. Accordingly, the length of the fragmented cylindrical micelles decreases as the phenol concentration increases (Figure 1). Until a high phenol concentration, the crystalline micelles become quasi-spherical, further fragmentation cannot occur. By contrast, since a single L-threonine molecule contains three H-bong-donating groups (two hydroxyls and one amino), the PEO blocks in the micellar corona may be dynamically cross-linked after complexation with L-threonine via H-bonding. This will lead to a more condensed structure of PEO and then a smaller reduced tethering density (σ̃).10 As a result, addition of L-threonine has a similar effect with addition of inorganic salts or increase of the pH value.56−58 At a smaller σ̃, the lateral surfaces at the ends of the micellar core are less covered by the corona-forming PEO block, then end-to-end coupling among the different crystalline micelles may occur, leading to growth of the micelles. The possible mechanism and reversible morphological transformation of the PCL-b-PEO crystalline micelles induced by phenol and L-threonine are schematically depicted in Scheme 1.

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AUTHOR INFORMATION

Corresponding Authors

*(J.-T.X.) E-mail: [email protected]. Telephone: +86-57187953164. Fax: +86-571-87952400. *(B.-Y.D.) E-mail: [email protected] Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China (21274130 and 21322406). REFERENCES

(1) He, W. N.; Xu, J. T. Prog. Polym. Sci. 2012, 37, 1350. (2) Schmelz, J.; Schacher, F. H.; Schmalz, H. Soft Matter 2013, 9, 2101. (3) Crassous, J. J.; Schurtenberger, P.; Ballauff, M.; Mihut, A. M. Polymer 2015, 62, A1. (4) Cao, L.; Manners, I.; Winnik, M. A. Macromolecules 2002, 35, 8258. (5) Hsiao, M. S.; Yusoff, S. F. M.; Winnik, M. A.; Manners, I. Macromolecules 2014, 47, 2361. (6) Schmelz, J.; Karg, M.; Hellweg, T.; Schmalz, H. ACS Nano 2011, 5, 9523. (7) Yin, L. G.; Hillmyer, M. A. Macromolecules 2011, 44, 3021. (8) Yin, L. G.; Lodge, T. P.; Hillmyer, M. A. Macromolecules 2012, 45, 9460. (9) Xu, J. T.; Jin, W.; Liang, G. D.; Fan, Z. Q. Polymer 2005, 46, 1709. (10) Du, Z. X.; Xu, J. T.; Fan, Z. Q. Macromolecules 2007, 40, 7633. (11) Du, Z. X.; Xu, J. T.; Fan, Z. Q. Macromol. Rapid Commun. 2008, 29, 467. (12) Mihut, A. M.; Crassous, J. J.; Schmalz, H.; Drechsler, M.; Ballauff, M. Soft Matter 2012, 8, 3163. (13) Rizis, G.; van de Ven, T. G. M.; Eisenberg, A. Angew. Chem., Int. Ed. 2014, 53, 9000. (14) Rizis, G.; van de Ven, T. G. M.; Eisenberg, A. ACS Nano 2015, 9, 3627. (15) Sun, L.; Petzetakis, N.; Pitto-Barry, A.; Schiller, T. L.; Kirby, N.; Keddie, D. J.; Boyd, B. J.; O’Reilly, R. K.; Dove, A. P. Macromolecules 2013, 46, 9074. (16) Sun, L.; Pitto-Barry, A.; Kirby, N.; Schiller, T. L.; Sanchez, A. M.; Dyson, M. A.; Sloan, J.; Wilson, N. R.; O’Reilly, R. K.; Dove, A. P. Nat. Commun. 2014, 5, 5746. (17) Li, Z. Y.; Liu, R.; Mai, B. Y.; Wang, W. J.; Wu, Q.; Liang, G. D.; Gao, H. Y.; Zhu, F. M. Polymer 2013, 54, 1663. (18) Wang, H.; Liu, C. L.; Wu, G.; Chen, S. C.; Song, F.; Wang, Y. Z. Soft Matter 2013, 9, 8712. (19) Wang, M. J.; Wang, H.; Chen, S. C.; Chen, C.; Liu, Y. Langmuir 2015, 31, 6971. (20) Gilroy, J. B.; Gädt, T.; Whittell, G. R.; Chabanne, L.; Mitchels, J. M.; Richardson, R. M.; Winnik, M. A.; Manners, I. Nat. Chem. 2010, 2, 566. (21) Qian, J. S.; Guerin, G.; Lu, Y. J.; Cambridge, G.; Manners, I.; Winnik, M. A. Angew. Chem., Int. Ed. 2011, 50, 1622. (22) Petzetakis, N.; Dove, A. P.; O’Reilly, R. K. Chem. Sci. 2011, 2, 955.

Scheme 1. Schematic Reversible Sphere-to-Cylindrical Transition for Crystalline Micelles of PCL-b-PEO Induced by Phenol and L-Threonine

4. CONCLUSIONS In conlusion, phenol can fragment the crystalline cylindrical micelles of PCL-b-PEO into short cylinders or quasi-spherical micelles, whereas L-threonine can induce a sphere-to-cylinder transition of PCL-b-PEO micelles, although both of phenol and L-threonine interact with the corona-forming PEO block via Hbonding. By adding these two compounds alternately, reversible morphological transformation can be realized for the crystalline micelles of PCL-b-PEO. Moreover, PCL-b-PEO BCPs are usually used in a biological enviornment due to their excellent biocompatibility, in which there exist lots of H-bond donors. Our findings in the present work will be also important for the applications of PCL-b-PEO BCPs.

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Effect of phenol on the micellar sizes of PCL46-b-PEO44 and PCL73-b-PEO44, change of the micellar size with time after addition of phenol, UV−vis spectra of PEO, phenol and their mixture, FT-IR spectra of PEO (Mn = 5000), PEO/phenol, and PEO/L-threonine mixtures, area ratio and height ratio of the IR bands for H-bonded and free C−O−C groups, effects of L-threonine concentration on micellar size, and molecular structure of L-threonine (PDF)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.5b02349. E

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(58) Yang, J. X.; He, W. N.; Xu, J. T.; Du, B. Y.; Fan, Z. Q. Chin. J. Polym. Sci. 2014, 32, 1128.

(23) He, W. N.; Zhou, B.; Xu, J. T.; Du, B. Y.; Fan, Z. Q. Macromolecules 2012, 45, 9768. (24) Fan, B.; Liu, L.; Li, J. H.; Ke, X. X.; Xu, J. T.; Du, B. Y.; Fan, Z. Q. Soft Matter 2016, 12, 67. (25) Wang, X. S.; Guerin, G.; Wang, H.; Wang, Y. S.; Manners, I.; Winnik, M. A. Science 2007, 317, 644. (26) Gädt, T.; Ieong, N. S.; Cambridge, G.; Winnik, M. A.; Manners, I. Nat. Mater. 2009, 8, 144. (27) Gilroy, J. B.; Patra, S. K.; Mitchels, J. M.; Winnik, M. A.; Manners, I. Angew. Chem., Int. Ed. 2011, 50, 5851. (28) Qiu, H. B.; Russo, G.; Rupar, P. A.; Chabanne, L.; Winnik, M. A.; Manners, I. Angew. Chem., Int. Ed. 2012, 51, 11882. (29) Hudson, Z. M.; Boott, C. E.; Robinson, M. E.; Rupar, P. A.; Winnik, M. A.; Manners, I. Nat. Chem. 2014, 6, 893. (30) Hudson, Z. M.; Lunn, D. J.; Winnik, M. A.; Manners, I. Nat. Commun. 2014, 5, 3372. (31) Cambridge, G.; Gonzalez-Alvarez, M. J.; Guerin, G.; Manners, I.; Winnik, M. A. Macromolecules 2015, 48, 707. (32) Qiu, H. B.; Gao, Y.; Du, V. A.; Harniman, R.; Winnik, M. A.; Manners, I. J. Am. Chem. Soc. 2015, 137, 2375. (33) Qiu, H. B.; Hudson, Z. M.; Winnik, M. A.; Manners, I. Science 2015, 347, 1329. (34) Schmelz, J.; Schedl, A. E.; Steinlein, C.; Manners, I.; Schmalz, H. J. Am. Chem. Soc. 2012, 134, 14217. (35) Guerin, G.; Wang, H.; Manners, I.; Winnik, M. A. J. Am. Chem. Soc. 2008, 130, 14763. (36) Massey, J. A.; Temple, K.; Cao, L.; Rharbi, Y.; Raez, J.; Winnik, M. A.; Manners, I. J. Am. Chem. Soc. 2000, 122, 11577. (37) Bhargava, P.; Tu, Y. F.; Zheng, J. X.; Xiong, H. M.; Quirk, R. P.; Cheng, S. Z. D. J. Am. Chem. Soc. 2007, 129, 1113. (38) Xiong, H. M.; Chen, C. K.; Lee, L. M.; Van Horn, R. M.; Liu, Z.; Ren, B.; Quirk, R. P.; Thomas, E. L.; Lotz, B.; Ho, R. M.; Zhang, W. B.; Cheng, S. Z. D. Macromolecules 2011, 44, 7758. (39) Wang, C. Y.; Yang, S. G.; Yu, X. F.; Zheng, J. X.; Ma, J. H.; Xu, J.; Zhu, M. F. Soft Matter 2012, 8, 10307. (40) Yang, S. G.; Yu, X. F.; Wang, L.; Tu, Y. F.; Zheng, J. X.; Xu, J. T.; Van Horn, R. M.; Cheng, S. Z. D. Macromolecules 2010, 43, 3018. (41) Salim, N. V.; Hanley, T. L.; Waddington, L. J.; Hartley, P. G.; Guo, Q. P. Macromol. Rapid Commun. 2012, 33, 401. (42) Salim, N. V.; Guo, Q. P. J. Phys. Chem. B 2011, 115, 9528. (43) Kuo, S. W. Polym. Int. 2009, 58, 455. (44) Chen, S. C.; Kuo, S. W.; Chang, F. C. Langmuir 2011, 27, 10197. (45) Lefèvre, N.; Fustin, C. A.; Gohy, J. F. Macromol. Rapid Commun. 2009, 30, 1871. (46) Lefèvre, N.; Fustin, C. A.; Gohy, J. F. Langmuir 2007, 23, 4618. (47) Xie, D. H.; Xu, K.; Bai, R. K.; Zhang, G. Z. J. Phys. Chem. B 2007, 111, 778. (48) Gao, W. P.; Bai, Y.; Chen, E. Q.; Li, Z. C.; Han, B. Y.; Yang, W. T.; Zhou, Q. F. Macromolecules 2006, 39, 4894. (49) Mata, J. P.; Majhi, P. R.; Kubota, O.; Khanal, A.; Nakashima, K.; Bahadur, P. J. Colloid Interface Sci. 2008, 320, 275. (50) Parekh, P.; Ganguly, R.; Aswal, V. K.; Bahadur, P. Soft Matter 2012, 8, 5864. (51) Khimani, M.; Ganguly, R.; Aswal, V. K.; Nath, S.; Bahadur, P. J. Phys. Chem. B 2012, 116, 14943. (52) Ganguly, R.; Kuperkar, K.; Parekh, P.; Aswal, V. K.; Bahadur, P. J. Colloid Interface Sci. 2012, 378, 118. (53) Du, Z. X.; Xu, J. T.; Yang, Y.; Fan, Z. Q. J. Appl. Polym. Sci. 2007, 105, 771. (54) Parekh, P.; Singh, K.; Marangoni, D. G.; Aswal, V. K.; Bahadur, P. Colloids Surf., A 2012, 400, 1. (55) Kim, Y. J.; Uyama, H.; Kobayashi, S. Macromolecules 2003, 36, 5058. (56) He, W. N.; Xu, J. T.; Du, B. Y.; Fan, Z. Q.; Wang, X. S. Macromol. Chem. Phys. 2010, 211, 1909. (57) He, W. N.; Xu, J. T.; Du, B. Y.; Fan, Z. Q.; Sun, F.-L. Macromol. Chem. Phys. 2012, 213, 952. F

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