Article Cite This: Macromolecules XXXX, XXX, XXX−XXX
Photoinduced Reversible Worm-to-Vesicle Transformation of AzoContaining Block Copolymer Assemblies Prepared by Polymerization-Induced Self-Assembly Qiquan Ye,† Meng Huo,† Min Zeng,† Lei Liu,† Liao Peng,† Xiaosong Wang,‡ and Jinying Yuan*,† †
Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China ‡ Department of Chemistry and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue, Waterloo, ON N2L 3G1, Canada S Supporting Information *
ABSTRACT: A series of azo-containing copolymeric assemblies based on poly(N,Ndimethylaminoethyl methacrylate)-b-poly[(benzyl methacrylate)-co-(4-phenylazophenyl methacrylate)] [PDMA-b-P(BzMA-co-AzoMA)] were prepared by reversible addition−fragmentation chain transfer polymerization-induced self-assembly at high solid contents. Depending on the chain length of P(BzMA-co-AzoMA), spheres, worms, and vesicles were readily prepared. These azo-containing wormlike micelles underwent reversible worm-to-vesicle transformation upon alternative UV/vis light irradiation. By investigating the morphology evolution, a series of intermediates were observed, including coalesced worms as well as “octopus”like and “jellyfish”-like structures. The morphology transformation was rationalized by the volume change of the P(BzMA-coAzoMA) block caused by the trans−cis isomerization of the azobenzene groups. It is the first demonstration of light-stimulated reversible worm-to-vesicle transition and would benefit for the understanding of morphology evolution of polymer assemblies under external stimuli.
■
micelles35 and vesicles36 were also reported. However, all of these assemblies are prepared using traditional postpolymerization self-assembly strategies, which were laborious and inefficient to target desired morphologies. Polymerization-induced self-assembly (PISA) is an emerging technique to prepare polymeric assemblies with controllable morphology and high concentration (10−50 wt %).23,37−41 Taking advantage of “living”/controlled dispersion or emulsion polymerization, PISA enables the preparation of amphiphilic block copolymer assemblies in situ via chain extension of the solvophilic block with solvophobic block.42−53 Compared with the traditional postpolymerization self-assembly strategies, PISA offers convenient size and morphology control, so a variety of morphologies, including spherical micelles, wormlike micelles (WLMs), nanosheets, and vesicles, can be easily produced.54−64 Taking advantage of PISA, Pan et al.65 fabricated photoresponsive polymeric vesicles via incorporation of spiropyran groups onto the solvophilic block. They prepared macro-chain-transfer agent (macro-CTA) by copolymerization of the spiropyran-derived methacrylate with 4-vinylpyridine and used this macro-CTA to mediate the PISA of styrene in methanol. This vesicle dispersion changed from colorless to red without morphology alteration upon UV irradiation, which corresponds to the spiropyran-to-merocyanine transformation.
INTRODUCTION Stimuli-responsive polymeric assemblies, which undergo changes in structures and properties in response to external stimuli, have been extensively studied for potential applications in the fields of artificial organelles,1,2 smart nanoreactors,3−6 drug and gene delivery,7−11 etc. Various stimuli, including temperature,12,13 pH,14 redox,15−17 salt,18,19 gas,20,21 and light,22,23 have been utilized to trigger the shape transformation of polymeric assemblies. Among these triggers, light stimulus enables precise regulation in intensity, duration time, and irradiation site, so that controlled stimuli response can be readily achieved without introducing additional reagents.24−31 For example, Zhao et al.32 prepared photoresponsive polymeric assemblies based on the azo-containing amphiphilic diblock copolymers poly(acrylic acid)-b-poly{6-[4-(4-methoxyphenylazo)phenoxy]hexyl methacroylate}. Because of the photoisomerization of the azobenzene mesogens, the micelles could be disrupted by ultraviolet (UV) irradiation and reformed by visible light. To study the photoinduced reversible fusion and fission of polymersomes, Zhou et al.33,34 prepared two kinds of micrometer-scale vesicles based on β-cyclodextrinand azobenzene-terminated poly(3-ethyl-3-oxetanemethanol)star-poly(ethylene glycol), respectively. Because of the host− guest molecular recognition between β-cyclodextrin and azobenzene units, these vesicles, after mixing up, aggregated and fused into vesicle aggregates, which underwent reversible fission and fusion upon UV/vis light trigger. Besides, reversible photocontrolled swelling−shrinking behaviors of spherical © XXXX American Chemical Society
Received: February 13, 2018 Revised: April 6, 2018
A
DOI: 10.1021/acs.macromol.8b00340 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
Scheme 1. (a) Preparation and Isomerization of Photoresponsive Copolymers; (b) Mechanism Insights of the Photoinduced Reversible Worm-to-Vesicle Transformation
Table 1. Summary of Feed Ratios, Monomer Conversions, Molecular Characteristics, and Nanostructures of Various Diblock Copolymer Assemblies Prepared by RAFT Dispersion Copolymerization in Ethanol at 70 °C feeda PDMA32-P(BzMA28-AzoMA3) PDMA32-P(BzMA60-AzoMA6) PDMA32-P(BzMA60-AzoMA6)-UVe PDMA32-P(BzMA120-AzoMA11)
conversion/%b
BzMA
AzoMA
30 80
3 8
120
12
BzMA 94.8 75.3 > 99
SEC
DLS
AzoMA
Mn/g mol−1
Đc
diameter/nmd
PDI
morphology
97.6 72.2
9500 13600 12700 15800
1.28 1.37 1.41 1.40
19.23 257.1 247.9 403.4
0.215 0.343 0.175 0.290
spheres worms vesicles vesicles
91.6
The feed molar ratio of the monomer to PDMA32. bConversions were calculated according to 1H NMR data. cĐ = Mw/Mn. dSphere-equivalent intensity-average diameter. eThe PDMA32-P(BzMA60-AzoMA6) copolymer after UV irradiation for 1 h.
a
By PISA, O’Reilly and Gibson et al.66 prepared poly(ethylene glycol)-b-poly(2-hydroxypropyl methacrylate) WLMs, which underwent worm-to-vesicle transition upon long-term light irradiation. Surprisingly, the photoinduced loss of end group caused the morphology transformation. However, the morphology transformation is irreversible, and how the WLMs evolve to vesicles upon external stimulus is still unknown. Herein, we report the photoresponsive worm-to-vesicle morphological evolution of a series of poly(N,N-dimethylaminoethyl methacrylate)-b-poly[(benzyl methacrylate)-co-(4phenylazophenyl methacrylate)] [PDMA-b-P(BzMA-coAzoMA)] copolymer assemblies. These assemblies are prepared by reversible addition−fragmentation chain transfer (RAFT) dispersion copolymerization of benzyl methacrylate (BzMA) and 4-phenylazophenyl methacrylate (AzoMA) (10 mol % of BzMA) mediated by the poly(N,N-dimethylaminoethyl methacrylate) (PDMA) macro-CTA at 15 wt % solids content. By changing the feed ratio of BzMA/PDMA, spherical micelles, WLMs, and vesicles could be successfully prepared. The reversible photoresponsive worm-to-vesicle shape evolution of these azo-containing WLMs is observed for the first time and studied by transmission electron microscopy (TEM), atomic force microscopy (AFM), ultraviolet−visible (UV−vis) spectroscopy, and dynamic light scattering (DLS).
■
removed through a short aluminum oxide column before use. Other reagents were used as received. All proton nuclear magnetic resonance (1H NMR) spectra were recorded on a 400 MHz JEOL JNM-ECA400 spectrometer using CDCl3 as the solvent. The molecular weights and dispersity values (Đ) of the polymers were determined by a Waters 1515 size exclusion chromatography (SEC) system at 35 °C with THF (containing 2% trimethylamine) as the eluent at a flow rate of 1 mL min−1. A series of narrow-dispersed polystyrene standards were used for SEC calibration. All the UV−vis spectra were recorded in ethanol by an Agilent Technologies Cary 100 spectrophotometer, and all the dispersions were diluted by 30 times (ca. 0.17 mg mL−1) for UV−vis measurement. The morphologies of the assemblies were characterized by a JEM-2010 TEM at an accelerating voltage of 120 kV and a Hitachi H-7650B TEM at 80 kV. To prepare the TEM samples, 10 μL of the dilute ethanolic dispersion of assemblies was dropped onto a carbon-coated copper grid and was adsorbed for 1 min before being blotted up. The TEM samples were stained with phosphotungstic acid solution to enhance the contrast of the TEM images. DLS measurements were carried out on a Marven Zetasizer Nano ZS90 with a He−Ne laser operating at 632.8 nm, and the 90° angle scattering light was detected. The height profiles of the assemblies were characterized by a Shimadzu SPM-9700 scanning probe microscope. Synthesis of AzoMA. AzoMA was synthesized as reported.68 4Phenylazophenol (4.955 g, 25 mmol) and triethylamine (3.795 g, 37.5 mmol) were dissolved into dichloromethane (250 mL) in a 500 mL round-bottomed flask. Methacryloyl chloride (3.136 g, 30 mmol) in dichloromethane (100 mL) was added dropwise into the 4phenylazophenol solution in an ice water bath. After stirring for 12 h at room temperature, the organic phase was extracted three times with 1 mol L−1 hydrochloric acid, 1 mol L−1 sodium bicarbonate solution, and deionized water in sequence and was then dried overnight with MgSO4. After evaporating the solvent, a yellow solid product was obtained. The crude product was purified by column chromatography on silica gel with petroleum ether/dichloromethane (4/1, v/v) as the eluent. The yield of AzoMA was 45.6%. 1H NMR
EXPERIMENTAL SECTION
Materials and Instrumentation. Azobis(isobutyronitrile) (AIBN) (99%), methacryloyl chloride (98%), and 4,4′-azobis(4cyanovaleric acid) (ACVA) (98%) were purchased from J&K Co. 4Phenylazophenol (97%) was purchased from Acros Organics. Benzyl methacrylate (BzMA) (98%) and N,N-dimethylaminoethyl methacrylate (DMA) (98%) were purchased from TCI (Shanghai). 4-(4Cyanopentanoic acid) dithiobenzoate (CPADB) was synthesized according to the previous literature.67 AIBN was recrystallized in ethanol and stored at −20 °C. For DMA and BzMA, inhibitors were B
DOI: 10.1021/acs.macromol.8b00340 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules (400 MHz, CDCl3) δ (ppm): 7.98−7.89 (m, 4H), 7.54−7.45 (m, 3H), 7.30−7.21 (m, 2H), 6.38 (m, 1H), 5.79 (m, 1H), 2.08 (dd, 3H). Synthesis of the PDMA Macro-CTA. PDMA32 (the subscript number denotes the number-average degree of polymerization) was synthesized through RAFT polymerization according to our previous report.69 ACVA (84 mg, 0.3 mmol), CPADB (502 mg, 1.8 mmol), and DMA (14.1 g, 90 mmol) were dissolved into 1,4-dioxane (30 mL) in a Schlenk flask. After nitrogen purging for 15 min, the mixture was stirred in an 80 °C oil bath for 6 h. The 1H NMR spectrum indicated that the monomer conversion reached 56%. The solution was quenched in liquid nitrogen and precipitated into n-hexane. The degree of polymerization (DP) of PDMA was 32 as characterized by 1 H NMR. Mn,SEC = 2.9 kg mol−1 and Mw,SEC/Mn,SEC = 1.33. 1H NMR (400 MHz, CDCl3) δ (ppm): 7.91−7.78 (m, 2H), 7.54−7.45 (m, 1H), 7.38−7.29 (m, 2H), 4.30−3.91 (m, 64H), 2.79−2.47 (m, 64H), 2.37− 2.19 (m, 194H), 2.00−1.67 (m, 62H), 1.25−0.74 (m, 102H). Synthesis of the PDMA-b-P(BzMA-co-AzoMA) Copolymers. A series of PDMA-b-P(BzMA-co-AzoMA) copolymers were synthesized by RAFT dispersion copolymerization at 15 wt % solids content (feed ratios and conversions are shown in Table 1). Taking PDMA32b-P(BzMA60-co-AzoMA6) as an example, AIBN (1.64 mg, 0.010 mmol), PDMA32 (0.265 g, 0.050 mmol), BzMA (0.705 g, 4.0 mmol), and AzoMA (0.107 g, 0.40 mmol) were dissolved into ethanol (6.03 g) in a Schlenk tube. After nitrogen bubbling for 30 min, the tube was stirred in a 70 °C oil bath for 12 h. After dialyzing in alcohol for 2 days, an aliquot of the dispersion was evaporated to dryness for 1H NMR and SEC characterizations, and the other dispersion was diluted to ca. 5.0 mg mL−1 by ethanol for further use. Mn,NMR = 17.2 kg mol−1, Mn,SEC = 13.6 kg mol−1, and Mw,SEC/Mn,SEC = 1.37. 1H NMR (400 MHz, CDCl3) δ (ppm): 7.98−7.75 (m, 23H), 7.55−7.40 (m, 22H), 7.39−7.00 (m, 364H), 5.07−4.74 (m, 121H), 4.24−3.94 (m, 64H), 2.77−2.48 (m, 64H), 2.43−2.17 (m, 195H), 2.17−1.59 (m, 178H), 1.54−0.60 (m, 343H). Irradiation Experiments. The UV irradiation experiments were conducted using a CEAULIGHT CEL-M500/350 UV irradiator equipped with a high-pressure mercury lamp (500 W). 10 mL of the dilute dispersion of assemblies (about 5.0 mg mL−1) in a quartz bottle was placed 5−10 cm away from the lamp. The temperature of the dispersion was kept under 35 °C with ventilation equipment. A PLSSXE300/300 UV irradiator with a xenon lamp and an L-42 band-pass filter was used to generate visible light with wavelength higher than 420 nm. 5 mL of the UV-irradiated dispersion of assemblies (about 5.0 mg mL−1) in a quartz bottle was placed 10−15 cm away from the lamp. The temperature of the sample was maintained to 25 °C using a water bath.
Figure 1. TEM images of PDMA32-b-P(BzMA60 -co-AzoMA6 ) assemblies (a) before and (c) after UV irradiation for 1 h. AFM images (b) before and (d) after UV irradiation. (e) UV−vis spectra and (f) DLS measurements of PDMA32-b-P(BzMA60-co-AzoMA6) before and after UV irradiation.
Having determined their morphologies, we then assessed the photoresponsiveness of these assemblies. First, the WLMs were characterized by UV−vis spectroscopy, which manifests an absorbance maximum at 326 nm, corresponding to the π−π* transition of the trans-azobenzene (Figure 1e). These WLMs were then illuminated by a high-pressure mercury lamp. After UV irradiation for 1 h, the absorbance maximum at 326 nm decreased by 32%, while the absorbance maximum at 440 nm increased (Figure 1e). As the absorbance maximum at 440 nm corresponds to the n−π* transition of cis-azobenzene, our results indicate the photoinduced trans-to-cis transition of azobenzene groups.72 Interestingly, TEM results indicate that these WLMs transform into vesicles with a mean diameter of 173 ± 39 nm (Figure 1c). The vesicular morphology is confirmed by the AFM image (Figure 1d), which shows a concave height profile with a higher periphery and a depressed central portion.73 Besides, the height of these vesicles is ca. 103 nm and the diameter is ca. 267 nm. Accompanied by the morphology transformation, DLS data show that the dispersity of the assemblies decreases from 0.343 to 0.115 (Figure 1f). The average hydrodynamic diameter (Dh) for nonspherical object as measured by DLS represents the hypothetical sphereequivalent hydrodynamic diameter. Thus, the size distribution of WLMs is generally quite broad. Therefore, it is reasonable for the observed decrease in the dispersity when the assemblies are converted to vesicles after UV irradiation. Moreover, the Dh of the vesicles is 205 ± 78 nm, which agrees with the mean diameter obtained by TEM. To understand the photoinduced worm-to-vesicle morphology transformation, we periodically sampled the dispersion for TEM, UV−vis, and DLS analyses. After UV irradiation for 1 min, the WLMs began to associate yielding branch points and small lamellae at the branch points (Figure 2b). After 5 min, nascent lamellae with “tentacles” (“octopus”-like assembles)
■
RESULTS AND DISCUSSION To prepare photoresponsive polymer assemblies by PISA, we design the RAFT dispersion copolymerization of BzMA and AzoMA in ethanol (Scheme 1), where AzoMA units act as the photoresponsive moiety and P(BzMA-co-AzoMA) chains act as the core-forming blocks. First, PDMA32 macro-CTA was synthesized by RAFT polymerization and characterized by the 1H NMR spectrum and SEC (Figures S1 and S2). We then performed the RAFT dispersion copolymerization of BzMA and AzoMA (10 mol % of BzMA) in ethanol using the PDMA32 as macro-CTA. By changing the feed ratio of BzMA/PDMA (Table 1), spheres, worms, and vesicles were obtained, which were revealed by TEM (Figure S4a, Figure 1a, and Figure S5a). The reactivity ratios of BzMA and AzoMA were calculated to be 0.61 and 1.25, respectively, according to their Alfrey−Price Q−e values (calculation details are shown as Supporting Information).70,71 Consequently, AzoMA is supposed to be introduced into the backbone randomly. For the PDMA32-bP(BzMA60-co-AzoMA6), AFM was also used to confirm the wormlike morphology (Figure 1b). C
DOI: 10.1021/acs.macromol.8b00340 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
Figure 2. TEM images of PDMA 32-b-P(BzMA60-co-AzoMA 6) assemblies (a) before and after UV irradiation for (b) 1, (c) 5, (d) 10, (e) 20, and (f) 60 min. (g) UV−vis spectra and (h) DLS profiles of PDMA32-b-P(BzMA60-co-AzoMA6) upon UV irradiation.
Figure 3. TEM images of the UV-irradiated PDMA32-b-P(BzMA60-coAzoMA6) assemblies (a) before and after visible light irradiation for (b) 5, (c) 10, (d) 20, (e) 30, and (f) 60 min. (g) UV−vis spectra and (h) DLS measurements of the UV-irradiated PDMA32-b-P(BzMA60-coAzoMA6) upon visible light irradiation.
were observed (Figure 2c). These “octopus”-like structures underwent partial wrap-up to form hemispherical “jellyfish”-like structures after UV irradiation for 10 min (Figure 2d). Stepwise, the “tentacles” of these “jellyfish” fused further, and vesicles with WLMs at the edge were observed after 20 min (Figure 2e). Finally, WLMs disappeared and pure vesicles formed after 60 min (Figure 2f). During the UV irradiation, the absorbance maximum at 326 nm decreased successively (Figure 2g), suggesting that the trans-azobenzene gradually isomerized into cis-azobenzene. Besides, the progressive reduction in the dispersity of the assemblies agrees with the TEM observation (Figure 2h). To evaluate the reversibility of the phototriggered morphology evolution, the above vesicular dispersion was exposed to visible light. After irradiation for 5 min, some short WLMs were observed besides vesicles (Figure 3b). Continuous irradiation led to the formation of more WLMs (Figure 3c). “Jellyfish”-like and “octopus”-like intermediates respectively appeared after 20 and 30 min (Figure 3d,e). Finally, most vesicles dissociated into WLMs after visible light irradiation for 60 min (Figure 3f). In contrast to the UV irradiation process, the absorbance maximum at 326 nm increased by 13% after 5 min of visible light irradiation (Figure 3g), which corresponded to about 90% of the initial absorbance value before UV irradiation, indicating a high-level reversibility. DLS results demonstrate that the dispersity of nano-objects increases gradually (Figure 3h), in accordance with the morphology evolution observed by TEM.
According to the results observed above, a three-step mechanism is proposed for the reversible worm-to-vesicle transition. First, WLMs associate to form branch points and small lamellae (“octopus”-like structures). Subsequently, the small lamellae extend, coalesce, and bend into hemispherical structures with some wormlike “tentacles” at the edge (“jellyfish”-like structures). Finally, the “tentacles” of the “jellyfish” undergo fusion, and the hemispherical “jellyfish”like structures transform into pure spherical vesicles. Conversely, the transformation process can be readily reversed upon visible light irradiation. In order to explore the driving force for the shape evolution, 1 H NMR spectra and SEC characterizations of the PDMA32-bP(BzMA60-co-AzoMA6) copolymer were carried out before and after UV irradiation to confirm the structural stability of the copolymer during the photo illumination (Figure S2, Figure S3, and Table 1). As both NMR and SEC reveal constant DPs and molecular weight, the possibility of photodegradation of the copolymer was excluded. Associating the changes in the structure with the morphology evolution of the copolymer, we speculate that the trans-to-cis transition of the azobenzene groups results in the morphological evolution of the WLMs. As reported, cis-azobenzene is bulkier than trans-azobenzne, so the trans-to-cis isomerization of azobenzene groups within the assemblies will increase the volume of the hydrophobic core.74,75 Conversely, the volume of hydrophobic core will D
DOI: 10.1021/acs.macromol.8b00340 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
vesicle transformation and reveals the morphology evolution under external stimuli, which is potentially useful for the development of smart polymer materials for drug carriers, nanoreactors, and nanorobotics.
decrease upon visible light exposure. According to the packing parameter p that determines the morphology of the assemblies v p= a0lc
■
where v represents the volume of the core-forming block, a0 represents the area of the hydrophilic−hydrophobic interface, and lc represents the length of the core-forming block, the increment of v leads to the increment of p, which could provide driving force for the shape transformation. Then, is the configuration switch of the azobenzene groups sufficient to drive the shape transformation of the WLMs? Since there is only a narrow phase region for WLMs in the typical phase diagram of block copolymer assemblies, a small change in p suffices to induce the transformation of WLMs into spherical micelles or vesicles. For example, Armes et al.76 found that during the RAFT aqueous dispersion polymerization of 2hydroxypropyl methacrylate (HPMA) using poly(glycerol monomethacrylate) (PGMA) as the macro-CTA, an increment of the DP of hydrophobic PHPMA by only 9% resulted in the morphology transition from partially coalesced WLMs (DP = 150) to vesicles (DP = 164). In addition, only ionization of the carboxyl end-groups of the PGMA−PHPMA also suffices to induce a worm-to-sphere transition.77 We thus attribute the worm-to-vesicle transformation to the photoisomerization of the azobenzene groups within the assemblies. Besides the PDMA32-b-P(BzMA60-co-AzoMA6) WLMs, the photoresponsiveness of the azo-containing spheres and vesicles was also assessed. For the spherical micelles, the UV irradiation can induce the trans-to-cis isomerization of the azobenzene groups, as confirmed by UV−vis spectra (Figure S4c). However, no obvious change in morphology or Dh of the spherical micelles was detected (Figure S4b,d). For the vesicles, the morphology and Dh also remained unchanged (Figure S5a,b,d). Different from the obvious changes of the UV−vis spectra of WLMs or spherical micelles, the UV−vis spectra of vesicles exhibit only minor decrease in the absorbance maximum of at 326 nm, and the absorbance maximum at 440 nm could not be identified (Figure S5c), which are rationalized by the size-dependent light scattering effect.69,78 The behaviors of the WLMs are different from the spheres and vesicles because the phase region of WLMs is much smaller than spheres and vesicles. In this work, there was only a small amount of AzoMA (10 mol % of BzMA) incorporated into the copolymers, so the photoisomerization of the azobenzene groups could only cause a small change of the volume of solvophobic block. Such a small change is sufficient to induce the morphology transformation of the WLMs, while it is not enough to cause evident morphologic variation of the spherical micelles or vesicles.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b00340. Synthetic route to the PDMA-b-P(BzMA-co-AzoMA) copolymers, 1H NMR spectra and SEC curves of the polymers, calculation details of the reactivity ratios of BzMA and AzoMA, TEM images, UV−vis spectra, and DLS curves of spherical micelles and vesicles before and after UV irradiation (PDF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected] (J.Y.). ORCID
Meng Huo: 0000-0001-8054-702X Xiaosong Wang: 0000-0002-6415-4768 Jinying Yuan: 0000-0002-1667-9252 Author Contributions
Q.Y. and M.H. contributed equally. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The National Natural Science Foundation of China (Project Nos. 51573086 and 21374053) is acknowledged for financial support. L. Pan and X. Xie in the Department of Chemical Engineering, Tsinghua University are acknowledged for the helpful discussions.
■
REFERENCES
(1) Tanner, P.; Baumann, P.; Enea, R.; Onaca, O.; Palivan, C.; Meier, W. Polymeric vesicles: from drug carriers to nanoreactors and artificial organelles. Acc. Chem. Res. 2011, 44, 1039−1049. (2) Tu, Y.; Peng, F.; Adawy, A.; Men, Y.; Abdelmohsen, L. K. E. A.; Wilson, D. A. Mimicking the cell: bio-inspired functions of supramolecular assemblies. Chem. Rev. 2016, 116, 2023−2078. (3) Lu, A.; O’Reilly, R. K. Advances in nanoreactor technology using polymeric nanostructures. Curr. Opin. Biotechnol. 2013, 24, 639−645. (4) Che, H.; van Hest, J. C. M. Stimuli-responsive polymersomes and nanoreactors. J. Mater. Chem. B 2016, 4, 4632−4647. (5) Stuart, M. A. C.; Huck, W. T. S.; Genzer, J.; Müller, M.; Ober, C.; Stamm, M.; Sukhorukov, G. B.; Szleifer, I.; Tsukruk, V. V.; Urban, M.; Winnik, F.; Zauscher, S.; Luzinov, I.; Minko, S. Emerging applications of stimuli-responsive polymer materials. Nat. Mater. 2010, 9, 101. (6) Zhang, J.; Li, X.; Li, X. Stimuli-triggered structural engineering of synthetic and biological polymeric assemblies. Prog. Polym. Sci. 2012, 37, 1130−1176. (7) Palivan, C. G.; Goers, R.; Najer, A.; Zhang, X.; Car, A.; Meier, W. Bioinspired polymer vesicles and membranes for biological and medical applications. Chem. Soc. Rev. 2016, 45, 377−411. (8) He, C.; Zhuang, X.; Tang, Z.; Tian, H.; Chen, X. Stimuli-sensitive synthetic polypeptide-based materials for drug and gene delivery. Adv. Healthcare Mater. 2012, 1, 48−78. (9) Meng, F.; Zhong, Z.; Feijen, J. Stimuli-responsive polymersomes for programmed drug delivery. Biomacromolecules 2009, 10, 197−209.
■
CONCLUSION In summary, a series of PDMA-b-P(BzMA-co-AzoMA) copolymers were prepared by PISA, and photoresponsive spherical micelles, WLMs, and vesicles were obtained by regulating the feed ratio of BzMA/PDMA. Reversible worm-tovesicle transformation was achieved under alternate UV/vis light irradiation. A series of intermediate morphologies, including coalesced worms as well as “octopus”-like and “jellyfish”-like structures, were revealed. The worm-to-vesicle transformation was attributed to the photoisomerization of the azobenzene groups within the assemblies. This discovery highlights the possibility of photoinduced reversible worm-toE
DOI: 10.1021/acs.macromol.8b00340 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
(32) Wang, G.; Tong, X.; Zhao, Y. Preparation of azobenzenecontaining amphiphilic diblock copolymers for light-responsive micellar aggregates. Macromolecules 2004, 37, 8911−8917. (33) Yan, D.; Zhou, Y.; Hou, J. Supramolecular self-assembly of macroscopic tubes. Science 2004, 303, 65−67. (34) Jin, H.; Zheng, Y.; Liu, Y.; Cheng, H.; Zhou, Y.; Yan, D. Reversible and large-scale cytomimetic vesicle aggregation: lightresponsive host−guest interactions. Angew. Chem., Int. Ed. 2011, 50, 10352−10356. (35) Chen, B.; Wang, Z.; Lu, J.; Yang, X.; Wang, Y.; Zhang, Z.; Zhu, J.; Zhou, N.; Li, Y.; Zhu, X. Cyclic azobenzene-containing amphiphilic diblock copolymers: solution self-assembly and unusual photoresponsive behaviors. Polym. Chem. 2015, 6, 3009−3013. (36) Han, K.; Su, W.; Zhong, M.; Yan, Q.; Luo, Y.; Zhang, Q.; Li, Y. Reversible photocontrolled swelling-shrinking behavior of micron vesicles self-assembled from azopyridine-containing diblock copolymer. Macromol. Rapid Commun. 2008, 29, 1866−1870. (37) Canning, S. L.; Smith, G. N.; Armes, S. P. A critical appraisal of RAFT-mediated polymerization-induced self-assembly. Macromolecules 2016, 49, 1985−2001. (38) Derry, M. J.; Fielding, L. A.; Armes, S. P. Polymerizationinduced self-assembly of block copolymer nanoparticles via RAFT non-aqueous dispersion polymerization. Prog. Polym. Sci. 2016, 52, 1− 18. (39) Charleux, B.; Delaittre, G.; Rieger, J.; D’Agosto, F. Polymerization-induced self-assembly: from soluble macromolecules to block copolymer nano-objects in one step. Macromolecules 2012, 45, 6753− 6765. (40) Rieger, J. Guidelines for the synthesis of block copolymer particles of various morphologies by RAFT dispersion polymerization. Macromol. Rapid Commun. 2015, 36, 1458−1471. (41) Pei, Y.; Lowe, A. B.; Roth, P. J. Stimulus-responsive nanoparticles and associated (reversible) polymorphism via polymerization induced self-assembly (PISA). Macromol. Rapid Commun. 2017, 38, 1600528. (42) Zhang, W.-J.; Hong, C.-Y.; Pan, C.-Y. Formation of hexagonally packed hollow hoops and morphology transition in RAFT ethanol dispersion polymerization. Macromol. Rapid Commun. 2015, 36, 1428−1436. (43) Tan, J.; Sun, H.; Yu, M.; Sumerlin, B. S.; Zhang, L. Photo-PISA: shedding light on polymerization-induced self-assembly. ACS Macro Lett. 2015, 4, 1249−1253. (44) Yeow, J.; Xu, J.; Boyer, C. Polymerization-induced self-assembly using visible light mediated photoinduced electron transfer−reversible addition−fragmentation chain transfer polymerization. ACS Macro Lett. 2015, 4, 984−990. (45) Yu, Q.; Ding, Y.; Cao, H.; Lu, X.; Cai, Y. Use of polyion complexation for polymerization-induced self-assembly in water under visible light irradiation at 25 °C. ACS Macro Lett. 2015, 4, 1293−1296. (46) Gao, P.; Cao, H.; Ding, Y.; Cai, M.; Cui, Z.; Lu, X.; Cai, Y. Synthesis of hydrogen-bonded pore-switchable cylindrical vesicles via visible-light-mediated RAFT room-temperature aqueous dispersion polymerization. ACS Macro Lett. 2016, 5, 1327−1331. (47) Zhang, B.; Lv, X.; An, Z. Modular monomers with tunable solubility: synthesis of highly incompatible block copolymer nanoobjects via RAFT aqueous dispersion polymerization. ACS Macro Lett. 2017, 6, 224−228. (48) Shi, P.; Qu, Y.; Liu, C.; Khan, H.; Sun, P.; Zhang, W. Redoxresponsive multicompartment vesicles of ferrocene-containing triblock terpolymer exhibiting on−off switchable pores. ACS Macro Lett. 2016, 5, 88−93. (49) Gao, C.; Zhou, H.; Qu, Y.; Wang, W.; Khan, H.; Zhang, W. In situ synthesis of block copolymer nanoassemblies via polymerizationinduced self-assembly in poly(ethylene glycol). Macromolecules 2016, 49, 3789−3798. (50) Zhou, W.; Qu, Q.; Xu, Y.; An, Z. Aqueous polymerizationinduced self-assembly for the synthesis of ketone-functionalized nanoobjects with low polydispersity. ACS Macro Lett. 2015, 4, 495−499.
(10) Alarcon, C. d. l. H.; Pennadam, S.; Alexander, C. Stimuli responsive polymers for biomedical applications. Chem. Soc. Rev. 2005, 34, 276−285. (11) Hoffman, A. S. Stimuli-responsive polymers: biomedical applications and challenges for clinical translation. Adv. Drug Delivery Rev. 2013, 65, 10−16. (12) Gibson, M. I.; O’Reilly, R. K. To aggregate, or not to aggregate? considerations in the design and application of polymeric thermallyresponsive nanoparticles. Chem. Soc. Rev. 2013, 42, 7204−7213. (13) Roy, D.; Brooks, W. L. A.; Sumerlin, B. S. New directions in thermoresponsive polymers. Chem. Soc. Rev. 2013, 42, 7214−7243. (14) Du, J.-Z.; Sun, T.-M.; Song, W.-J.; Wu, J.; Wang, J. A tumoracidity-activated charge-conversional nanogel as an intelligent vehicle for promoted tumoral-cell uptake and drug delivery. Angew. Chem., Int. Ed. 2010, 49, 3621−3626. (15) Huo, M.; Yuan, J.; Tao, L.; Wei, Y. Redox-responsive polymers for drug delivery: from molecular design to applications. Polym. Chem. 2014, 5, 1519−1528. (16) Peng, L.; Feng, A.; Huo, M.; Yuan, J. Ferrocene-based supramolecular structures and their applications in electrochemical responsive systems. Chem. Commun. 2014, 50, 13005−13014. (17) Zhang, Q.; Re Ko, N.; Kwon Oh, J. Recent advances in stimuliresponsive degradable block copolymer micelles: synthesis and controlled drug delivery applications. Chem. Commun. 2012, 48, 7542−7552. (18) Abdelmohsen, L. K. E. A.; Williams, D. S.; Pille, J.; Ozel, S. G.; Rikken, R. S. M.; Wilson, D. A.; van Hest, J. C. M. Formation of welldefined, functional nanotubes via osmotically induced shape transformation of biodegradable polymersomes. J. Am. Chem. Soc. 2016, 138, 9353−9356. (19) Li, Y.; Wang, Y.; Huang, G.; Ma, X.; Zhou, K.; Gao, J. Chaotropic-anion-induced supramolecular self-assembly of ionic polymeric micelles. Angew. Chem., Int. Ed. 2014, 53, 8074−8078. (20) Yan, Q.; Wang, J.; Yin, Y.; Yuan, J. Breathing polymersomes: CO2-tuning membrane permeability for size-selective release, separation, and reaction. Angew. Chem., Int. Ed. 2013, 52, 5070−5073. (21) Yan, Q.; Zhou, R.; Fu, C.; Zhang, H.; Yin, Y.; Yuan, J. CO2responsive polymeric vesicles that breathe. Angew. Chem., Int. Ed. 2011, 50, 4923−4927. (22) Wang, D.; Wang, X. Amphiphilic azo polymers: molecular engineering, self-assembly and photoresponsive properties. Prog. Polym. Sci. 2013, 38, 271−301. (23) Sun, J.-T.; Hong, C.-Y.; Pan, C.-Y. Recent advances in RAFT dispersion polymerization for preparation of block copolymer aggregates. Polym. Chem. 2013, 4, 873−881. (24) Zhao, Y. Photocontrollable block copolymer micelles: what can we control? J. Mater. Chem. 2009, 19, 4887−4895. (25) Klajn, R. Spiropyran-based dynamic materials. Chem. Soc. Rev. 2014, 43, 148−184. (26) Wang, J.; Wang, S.; Zhou, Y.; Wang, X.; He, Y. Fast photoinduced large deformation of colloidal spheres from a novel 4arm azobenzene compound. ACS Appl. Mater. Interfaces 2015, 7, 16889−16895. (27) Wang, J.; Wu, B.; Li, S.; Sinawang, G.; Wang, X.; He, Y. Synthesis and characterization of photoprocessable lignin-based azo polymer. ACS Sustainable Chem. Eng. 2016, 4, 4036−4042. (28) Li, S.; Wang, J.; Shen, J.; Wu, B.; He, Y. Azo coupling reaction induced macromolecular self-assembly in aqueous solution. ACS Macro Lett. 2018, 7, 437−441. (29) Jian, C.-m.; Liu, B.-w.; Chen, X.; Zhou, S.-t.; Fang, T.; Yuan, J.-y. Construction of photoresponsive supramolecular micelles based on ethyl cellulose graft copolymer. Chin. J. Polym. Sci. 2014, 32, 690−702. (30) Zhang, H. J.; Xin, Y.; Yan, Q.; Zhou, L. L.; Peng, L.; Yuan, J. Y. Facile and efficient fabrication of photoresponsive microgels via thiol− michael addition. Macromol. Rapid Commun. 2012, 33, 1952−1957. (31) Yan, Q.; Xin, Y.; Zhou, R.; Yin, Y.; Yuan, J. Light-controlled smart nanotubes based on the orthogonal assembly of two homopolymers. Chem. Commun. 2011, 47, 9594−9596. F
DOI: 10.1021/acs.macromol.8b00340 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
(68) Wu, S.; Zhu, X.; Yang, J.; Nie, J. A facile photopolymerization method for fabrication of pH and light dual reversible stimuliresponsive surfaces. Chem. Commun. 2015, 51, 5649−5651. (69) Huo, M.; Ye, Q.; Che, H.; Wang, X.; Wei, Y.; Yuan, J. Polymer assemblies with nanostructure-correlated aggregation-induced emission. Macromolecules 2017, 50, 1126−1133. (70) Otsu, T.; Ito, T.; Imoto, M. The reactivities of alkyl methacrylates in their radical polymerizations. J. Polym. Sci., Part B: Polym. Lett. 1965, 3, 113−117. (71) Braun, D.; Czerwinski, W. K.; Tüdő s, F.; Turcsanyi, B.; Kelen, T. Analysis of the linear methods for determining copolymerization reactivity ratios, VIII. A critical reexamination of radical copolymerization of methylmethacrylate or styrene. Angew. Makromol. Chem. 1990, 178, 209−219. (72) Kumar, G. S.; Neckers, D. C. Photochemistry of azobenzenecontaining polymers. Chem. Rev. 1989, 89, 1915−1925. (73) Jain, S.; Bates, F. S. Consequences of nonergodicity in aqueous binary PEO−PB micellar dispersions. Macromolecules 2004, 37, 1511− 1523. (74) Hamada, T.; Sato, Y. T.; Yoshikawa, K.; Nagasaki, T. Reversible photoswitching in a cell-sized vesicle. Langmuir 2005, 21, 7626−7628. (75) Klajn, R. Immobilized azobenzenes for the construction of photoresponsive materials. Pure Appl. Chem. 2010, 82, 2247. (76) Blanazs, A.; Madsen, J.; Battaglia, G.; Ryan, A. J.; Armes, S. P. Mechanistic insights for block copolymer morphologies: how do worms form vesicles? J. Am. Chem. Soc. 2011, 133, 16581−16587. (77) Lovett, J. R.; Warren, N. J.; Ratcliffe, L. P. D.; Kocik, M. K.; Armes, S. P. pH-responsive non-ionic diblock copolymers: ionization of carboxylic acid end-groups induces an order−order morphological transition. Angew. Chem., Int. Ed. 2015, 54, 1279−1283. (78) Chen, J.; Law, C. C. W.; Lam, J. W. Y.; Dong, Y.; Lo, S. M. F.; Williams, I. D.; Zhu, D.; Tang, B. Z. Synthesis, light emission, nanoaggregation, and restricted intramolecular rotation of 1,1substituted 2,3,4,5-tetraphenylsiloles. Chem. Mater. 2003, 15, 1535− 1546.
(51) Fu, W.; Luo, C.; Morin, E. A.; He, W.; Li, Z.; Zhao, B. UCSTtype thermosensitive hairy nanogels synthesized by RAFT polymerization-induced self-assembly. ACS Macro Lett. 2017, 6, 127−133. (52) Huo, M.; Li, D.; Song, G.; Zhang, J.; Wu, D.; Wei, Y.; Yuan, J. Semi-fluorinated methacrylates: a class of versatile monomers for polymerization-induced self-assembly. Macromol. Rapid Commun. 2018, 39, 1700840. (53) Qiao, X. G.; Lansalot, M.; Bourgeat-Lami, E.; Charleux, B. Nitroxide-mediated polymerization-induced self-assembly of poly(poly(ethylene oxide) methyl ether methacrylate-co-styrene)-b-poly(n-butyl methacrylate-co-styrene) amphiphilic block copolymers. Macromolecules 2013, 46, 4285−4295. (54) Blanazs, A.; Verber, R.; Mykhaylyk, O. O.; Ryan, A. J.; Heath, J. Z.; Douglas, C. W. I.; Armes, S. P. Sterilizable gels from thermoresponsive block copolymer worms. J. Am. Chem. Soc. 2012, 134, 9741−9748. (55) Gonzato, C.; Semsarilar, M.; Jones, E. R.; Li, F.; Krooshof, G. J. P.; Wyman, P.; Mykhaylyk, O. O.; Tuinier, R.; Armes, S. P. Rational synthesis of low-polydispersity block copolymer vesicles in concentrated solution via polymerization-induced self-assembly. J. Am. Chem. Soc. 2014, 136, 11100−11106. (56) Warren, N. J.; Mykhaylyk, O. O.; Ryan, A. J.; Williams, M.; Doussineau, T.; Dugourd, P.; Antoine, R.; Portale, G.; Armes, S. P. Testing the vesicular morphology to destruction: birth and death of diblock copolymer vesicles prepared via polymerization-induced selfassembly. J. Am. Chem. Soc. 2015, 137, 1929−1937. (57) Huo, M.; Zeng, M.; Li, D.; Liu, L.; Wei, Y.; Yuan, J. Tailoring the multicompartment nanostructures of fluoro-containing ABC triblock terpolymer assemblies via polymerization-induced selfassembly. Macromolecules 2017, 50, 8212−8220. (58) Huo, M.; Zhang, Y.; Zeng, M.; Liu, L.; Wei, Y.; Yuan, J. Morphology evolution of polymeric assemblies regulated with fluorocontaining mesogen in polymerization-induced self-assembly. Macromolecules 2017, 50, 8192−8201. (59) Yao, H.; Ning, Y.; Jesson, C. P.; He, J.; Deng, R.; Tian, W.; Armes, S. P. Using host−guest chemistry to tune the kinetics of morphological transitions undertaken by block copolymer vesicles. ACS Macro Lett. 2017, 6, 1379−1385. (60) Jia, Z.; Bobrin, V. A.; Truong, N. P.; Gillard, M.; Monteiro, M. J. Multifunctional nanoworms and nanorods through a one-step aqueous dispersion polymerization. J. Am. Chem. Soc. 2014, 136, 5824−5827. (61) Huo, M.; Xu, Z.; Zeng, M.; Chen, P.; Liu, L.; Yan, L.-T.; Wei, Y.; Yuan, J. Controlling vesicular size via topological engineering of amphiphilic polymer in polymerization-induced self-assembly. Macromolecules 2017, 50, 9750−9759. (62) He, W.-D.; Sun, X.-L.; Wan, W.-M.; Pan, C.-Y. Multiple morphologies of PAA-b-PSt assemblies throughout RAFT dispersion polymerization of styrene with PAA macro-CTA. Macromolecules 2011, 44, 3358−3365. (63) Blackman, L. D.; Varlas, S.; Arno, M. C.; Fayter, A.; Gibson, M. I.; O’Reilly, R. K. Permeable protein-loaded polymersome cascade nanoreactors by polymerization-induced self-assembly. ACS Macro Lett. 2017, 6, 1263−1267. (64) Huo, M.; Zeng, M.; Wu, D.; Wei, Y.; Yuan, J. Topological engineering of amphiphilic copolymers via RAFT dispersion copolymerization of benzyl methacrylate and 2-(perfluorooctyl)ethyl methacrylate for polymeric assemblies with tunable nanostructures. Polym. Chem. 2018, 9, 912−919. (65) Huang, C.-Q.; Wang, Y.; Hong, C.-Y.; Pan, C.-Y. Spiropyranbased polymeric vesicles: preparation and photochromic properties. Macromol. Rapid Commun. 2011, 32, 1174−1179. (66) Blackman, L. D.; Doncom, K. E. B.; Gibson, M. I.; O’Reilly, R. K. Comparison of photo- and thermally initiated polymerizationinduced self-assembly: a lack of end group fidelity drives the formation of higher order morphologies. Polym. Chem. 2017, 8, 2860−2871. (67) Huo, M.; Ye, Q.; Che, H.; Sun, M.; Yuan, J.; Wei, Y. Synthesis and self-assembly of CO2-responsive dendronized triblock copolymers. Polym. Chem. 2015, 6, 7427−7435. G
DOI: 10.1021/acs.macromol.8b00340 Macromolecules XXXX, XXX, XXX−XXX
