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. 2017 Jan 13;2(1):105–112. doi: 10.1021/acsomega.6b00327

Thermoresponsive Pyrrolidone Block Copolymer Organogels from 3D Micellar Networks

Shuozhen Cheng †, Yan Xue †, Yechang Lu †,‡, Xuefeng Li †,*, Jinfeng Dong †,*
PMCID: PMC6640968  PMID: 31457214

Abstract

graphic file with name ao-2016-003273_0001.jpg

A new series of amphiphilic pyrrolidone diblock copolymers poly[N-(2-methacrylaoyxyethyl)pyrrolidone]-block-poly(methyl methacrylate) (PNMPm-b-PMMAn; where m is fixed at 37 and n is varied from 45 to 378) is developed. Spontaneously situ-gelling behaviors are observed in isopropanol when n varies from 117 to 230, whereas only dissolution or precipitation appears when n is beyond this region. Further analysis reveals that uniform thermoinduced reversible gel–sol transitions are observed in those organogels, which is attributed to the disassembly from micellar networks to micelles as confirmed by electron microscopy and other techniques. The gel–sol transition temperature is highly dependent on n and increases as n increases. Conformational interactions analyzed using 1H NMR and 2D Noesy NMR suggest that the thermoinduced stretch of solvophilic PNMP segments within micelles and the sequencing variation in the isopropanol molecules are the major cause of the gel–sol transitions.

Introduction

Amphiphilic block copolymers can form self-organized nanostructures in solutions with diversified morphologies such as spherical and cylindrical micelles, vesicles, and fibers, which are widely used in the development of self-healing materials,1−3 drug-controlled release systems,4−6 catalysis,7,8 and so forth. Such polymers with controllable solvophobic–solvophilic balance by regulating environmental factors such as pH, temperature, light, and electric field, or stimuli-responsive block copolymers, are extremely interesting because their nanostructure morphologies are controllable.9−12 Development of structurally controllable stimuli-responsive block copolymers, especially those with low toxicity and excellent biocompatibility, as well as their self-assembly behaviors, which are critically important in the fields of medicine, life, biotechnology, and environment, is one of the most attractive topics currently.13−16

Polymer gels are often considered a category of supermolecular 3D networks17 of fiber-, line-, and ribbonlike nanostructures and are advantageous because of their hydrogen bonds,18,19 dynamic covalent bonds,20 π–π21 and coordination22−24 interactions, and so forth. Recently, a new type of gels composed of 3D micellar networks that realized the transitions between spherical polymer micelles and 3D micellar gels reversibly through adjusting the temperature was also reported.25−29 For example, Gupta and co-authors reported a thermoresponsive 3D micellar gel based on the cyto-protective triblock copolymer poly[(propylenesulfide)-block-(N,N-dimethylacylamide)-block-(N-isopropylacrylamide)], which was used in the controlled release of drugs in vivo successfully.30 The chemical composition, polymerization degree, and the ratio of blocks with different properties of block copolymers all affect the gelling behaviors strongly. In other words, the nature of the polymer is primary in those gelling processes.31 In addition, the importance of solvents cannot be neglected because it affects the overall solvophobic–solvophilic balance of diblock copolymers directly.17

Pyrrolidone has been a well-known environmentally friendly chemical for decades and is rarely used in the development of block copolymers although its polymeric form, polyvinylpyrrolidone, has been used widely.32−36 We first reported a controllable way to develop pyrrolidone-based block copolymer amphiphiles, poly(methacrylic acid)-block-poly[N-(2-methacryloylxyethyl)pyrrolidone] (PMAA-b-PNMP)37 and poly(laurylmethacrylate)-block-poly[N-(2-methacryloylxyethyl)pyrrolidone] (PLMA-b-PNMP),38 which showed interesting aggregation behaviors and were used to control the formation of gold nanoparticles successfully. Recently, Armes have reported that self-organized nano-objects of poly(stearylmethacrylate)-block-poly[N-(2-methacryloyloxyethyl)pyrrolidone] (PSMA-b-PNMP), the homologous of PLMA-b-PNMP, in dodecane were excellent emulsifiers to stabilize Pickering emulsions.39 The major difference between PLMA-b-PNMP and PMAA-b-PNMP comes from the hydrophobic PLMA and the hydrophilic PMAA segments. The structural similarity between PLMA and PMAA provides an alternative way to adjust the solvophobic–solvophilic balance of the pyrrolidone diblock copolymers through altering the alkyl chain length of methacrylate monomers, thereby manipulating the self-assembly behaviors to expand the corresponding applications.

Herein, a new family of pyrrolidone diblock copolymers PNMP-b-PMMA, poly[N-(2-methacrylaoyxyethyl)pyrrolidone]-block-poly(methyl methacrylate), is developed using the reversible addition–fragmentation chain transfer (RAFT) method successfully. The self-assembly behavior of PNMP-b-PMMA in isopropanol is established, which leads to the finding of a new category of 3D micellar networks organogels. The microstructure and thermoresponse of those organogels are studied in detail by various techniques including rheology, light scattering, and electron microscopy. The conformational changes in both block copolymers and solvent molecules during the gel–sol transition are also investigated by the nuclear magnetic resonance (NMR) spectra at the molecular level systematically.

Results and Discussion

PNMP-b-PMMA Block Copolymers

All PNMP-b-PMMA block copolymers are synthesized using the RAFT polymerization method38 and are characterized using 1H NMR, gel permeation chromatography (GPC) well, which are summarized in Table 1, and are described in detail in the Experimental Section and Figures S1–S3. The polymerization degree of the PNMP segment for PNMP-b-PMMA is kept constant at 37, whereas that of the PMMA segment is varied in a wide range between 45 and 378 to ensure sufficient solvophobic–solvophilic balance variation in PNMP-b-PMMA, thereby leading to a rich self-assembly behavior.

Table 1. Molecular Information of PNMP-b-PMMA.

  yield GPC
 1H NMR
PNMPm-b-PMMAna (%) Mn (g·mol–1) Mw/Mn Mn (g·mol–1)
PNMP37-b-PMMA45 72 14 890 1.02 12 105
PNMP37-b-PMMA87 75 19 050 1.03 16 249
PNMP37-b-PMMA117 77 22 630 1.02 19 283
PNMP37-b-PMMA151 67 26 620 1.03 22 687
PNMP37-b-PMMA189 70 31 110 1.04 26 498
PNMP37-b-PMMA230 45 35 520 1.01 30 523
PNMP37-b-PMMA269 65 38 910 1.02 33 047
PNMP37-b-PMMA293 70 41 670 1.05 36 895
PNMP37-b-PMMA323 67 46 090 1.06 39 818
PNMP37-b-PMMA378 72 52 650 1.05 45 331
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a

The polymerization degree m and n of PNMP and PMMA segments are calculated from the 1H NMR results.

It is known that isopropanol is a good solvent for PNMP homopolymers and a poor one for PMMA homopolymers.40 Thus, the PNMP and PMMA segments of PNMP-b-PMMA block copolymers are expected to play the role as solvophilic and solvophobic parts, respectively, providing PNMP-b-PMMA amphiphilicity in isopropanol. Because the solvophilic PNMP parts are kept constant in all polymers, the increase in n should enhance its solvophobicity and the micellization ability of those block copolymers. The critical micelle concentrations (cmc) of PNMP37-b-PMMA117, PNMP37-b-PMMA151, PNMP37-b-PMMA189, and PNMP37-b-PMMA230 measured using static light scattering (SLS) are 0.026, 0.016, 0.015, and 0.013 wt % (Figure S4a), respectively, confirming that PNMP37-b-PMMAn with a larger n favors micellization evidently. Dynamic light scattering (DLS) results show that the micellar size is increased upon increasing n (Figure S4b) because of the increase in the solvophobic micellar core. In addition,38 the morphology of micelles is spherical as observed from the transmission electron microscopy measurements (Figure S4c).

In addition, the self-assembly behavior of PNMP-b-PMMA block copolymers in isopropanol shows high dependency on n. Opaque organogels are formed when n is between 117 and 230, whereas only dissolution or precipitation is observed for others (Figure S5a). Moreover, those organogels can transform into transparent solutions upon heating (Figure S5b) and regelling reversibly through cooling, indicating the typical behavior of thermoresponsive gels, which will be discussed further in the next section.

PNMP-b-PMMA Organogels in Isopropanol

The dynamic strain-sweeping results of 5 wt % PNMP-b-PMMA organogels (Figure 1a) show that both the storage modulus G′ and the loss modulus G″ remain almost invariable on gradually increasing the strain in a wide region, with G′ remaining over G″, and then dropping sharply above a critical stain value for each copolymer, corresponding to the mechanical break of organogels.41 It is also noticed that the values of G′ and G″ as well as the critical strain value are increased for PNMP-b-PMMA with a larger n, suggesting that the increase in n strengthens the mechanical intensity of organogels. Moreover, the organogels have relatively high yield stresses of approximately 100 Pa except that of PNMP37-b-PMMA117, indicating that very stable microstructures are formed. Figure 1b shows the corresponding dynamic frequency-sweeping results of PNMP-b-PMMA that the storage modulus G′ is generally larger than the loss modulus G″ regardless of frequency, indicating that the organogels mainly exhibit elasticity.42

Figure 1.

Figure 1

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The dynamic strain-sweeping (a) and frequency-sweeping (b) results of 5 wt % PNMP-b-PMMA organogels in isopropanol at 20 °C; the open and solid symbols represent G′ and G″, respectively.

Figure 2 shows the corresponding microstructures of 5 wt % PNMP-b-PMMA organogels in isopropanol, and all samples are freeze-dried before the scanning electron microscopy (SEM) observations. Similar coral-like microstructures, corresponding to the cross-linked nanoparticles with a size of approximately tens of nanometers, are observed in all organogel samples, suggesting that the organogels are composed of 3D networks of PNMP-b-PMMA spherical micelles directly. As mentioned in the Introduction section, fiber-, line-, or ribbon-like microstructures are often dominant in gelation systems.17 However, similar situ-gelling processes based on 3D micellar networks are rarely reported,43 and the delicate balance between solvency and nonsolvency of a block copolymer,44 or the solvophobic–solvophilic balance, is the major cause. For example, the polyethylene glycol segment is often used to design the copolymer gels with 3D micellar networks through adjusting the interactions between block copolymers and solvents.45

Figure 2.

Figure 2

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SEM images of the 5 wt % PNMP-b-PMMA organogels in isopropanol at 20 °C. (a) PNMP37-b-PMMA117, (b) PNMP37-b-PMMA151, (c) PNMP37-b-PMMA189, and (d) PNMP37-b-PMMA230. Bars represent 200 nm.

Thermoresponse of PNMP-b-PMMA Organogels

The thermoinduced gel–sol transitions of PNMP-b-PMMA organogels are investigated using turbidity, as shown in Figure 3a. Clearly, the transmittance is increased steeply at a given temperature for each PNMP-b-PMMA upon heating and returns reversibly through cooling, indicating that the gel–sol transition is reversible. The gel–sol transition temperature is a function of the polymerization degree n of the PMMA segment. The larger the n, the higher the transition temperature. For example, the temperatures of PNMP37-b-PMMA117 and PNMP37-b-PMMA230 are approximately 27 and 50 °C, respectively. It is reasonable because the solvophobic interactions of PNMP-b-PMMA are strengthened by increasing the polymerization degree n of the PMMA segment. Further analysis shows that the gel–sol transition temperature is also related to the concentration of PNMP-b-PMMA strongly (Figure 3b). The transition temperature increases as the polymer concentration increases in the low concentration region (<5 wt %) and then becomes nearly constant for each block copolymer, and a similar finding was previously reported in other gelling systems.46

Figure 3.

Figure 3

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(a) Temperature-dependent transmittance of 5 wt % PNMP-b-PMMA in isopropanol upon heating and cooling. (b) Concentration-dependent gel–sol transition temperature of PNMP-b-PMMA organogels.

To understand the nature of PNMP-b-PMMA in isopropanol solution, 5 wt % PNMP37-b-PMMA117 is representatively studied further using DLS and cryogenic TEM (cryo-TEM) techniques because of its lower gel–sol transition temperature (Figure 3a). Figure 4a shows the particle size distribution at various temperatures. Obviously, the presence of particles with a radius (Rh) of approximately tens of nanometers in the solution was confirmed by cryo-TEM imaging, suggesting the formation of micelles (Figure 4b). The inset image in Figure 4a shows the variation in the micellar size with the temperature. The higher the temperature, the smaller the size. It is worthwhile to mention that the average diameter of micelles is determined using the cryo-TEM image to be approximately 22 nm (Figure S6), which is consistent with the size measured using DLS (∼20 nm) in a 50 °C well, yet it is smaller than the other temperatures. This can be attributed to the thermoinduced thinning in the solvable layer of micelles and the dispersion of connected micelles,47 which is also the major cause in the temperature-induced micellar size decrease (the inset image in Figure 4a).

Figure 4.

Figure 4

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Temperature-dependent size distribution of 5 wt % PNMP37-b-PMMA117 in isopropanol (a) and the corresponding cryo-TEM image (b) at 30 °C. The inset image in (a) represents the effect of temperature on aggregate size.

Molecular Interactions of PNMP-b-PMMA in Organogels and Solution States

Electron microscopy results indicate that the thermoinduced gel–sol transitions are attributed to the disassembly of micellar networks, and the microenvironmental variation in PNMP-b-PMMA is further studied by NMR techniques at the molecular level. Figure 5 shows the 1H NMR spectra of 5 wt % PNMP37-b-PMMA151, the polymer with a typical gel–sol transition temperature of approximately 39 °C (Figure 3a), in d8-isopropanol.

Figure 5.

Figure 5

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Temperature-dependent 1H NMR spectra of 5 wt % PNMP37-b-PMMA151 in d8-isopropanol, and the inset images show the molecular structures of PNMP37-b-PMMA151 and isopropanol.

No obvious chemical shift is observed at different temperatures. However, the resolution and intensity of peaks for nearly all protons are strengthened significantly above 40 °C, which is well consistent with its gel–sol transition temperature. Similar results are also observed in other amphiphilic systems and are often attributed to the formation of smaller aggregates because the polymeric chains become less restricted.48 The proton signals in 1H NMR spectra are often highly related to the location of their microenvironments. Herein, the solvophobic PMMA segments are located in the micellar core both in the organogel and in the solution states; hence, little changes in the microenvironments are observed. However, the solvophilic PNMP segments come in contact with isopropanol directly, and thereby, the thermoinduced disassembly of micellar networks should mainly be caused by the microenvironmental changes in the PNMP segments.

Figure 6a,b shows the 2D Noesy NMR spectra of 5 wt % PNMP37-b-PMMA151 in both organogels and solution states. Significant conformational changes in both block copolymers and solvents are observed from the cross-peaks as signed by the boxes 1–3 in Figure 6a. For the diblock copolymer PNMP37-b-PMMA151, remarkable conformational interactions from the PNMP segments in the organogel state including those between Ha and Hc (box 1), Hd,e and Hg, and Hd,e and Hf (box 3) are observed at 25 °C, which disappeared completely in the solution state at 55 °C. However, nearly no visible conformational interactions are observed from the proton Hh of the PMMA segments regardless of the environmental temperature. The results evidently show that the gel–sol transition is mainly attributed to the microenvironmental changes in the solvophilic PNMP parts of the block copolymers, indicating that those moieties including the pyrrolidone rings and the main chains of block copolymers in micelles must be packed very closely in the gelling state.

Figure 6.

Figure 6

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2D Noesy NMR spectra of 5 wt % PNMP37-b-PMMA151 in d8-isopropanol at 25 (a) and 55 °C (b), respectively.

It should be mentioned that the conformational interactions marked by boxes 1 and 3 might come from both the coiled PNMP segments within the micelles and the interdigitated solvophilic PNMP layers of different micelles. Undoubtedly, the distance between the pyrrolidone ring and the main chain of the block copolymers should be widened in the solution state, or in other words, the PNMP segments become more stretched in the solution than in the gelling state, resulting in the weakening of all conformational interactions from the PNMP segments. Simultaneously, similar findings are also observed in the residual protons of solvents that the strong conformational interactions between H1 and H2 (box 2) of isopropanol molecules in the organogel are also invisible in the solution, suggesting that heating also weakens the conformational interactions of isopropanol molecules. It is well-known that the molecular thermodynamic movement would be enhanced upon increasing the temperature,49 thereby weakening the conformational interactions of the isopropanol molecules.

Conclusions

In summary, we report a new family of pyrrolidone-based amphiphilic diblock copolymers PNMPm-b-PMMAn, which are synthesized using the controlled RAFT polymerization method. It is noticed that their self-assembly behaviors in isopropanol depend strongly on the polymerization degree n of PMMA when the polymerization degree m of PNMP is fixed at 37. More interestingly, these copolymers form thermoresponsive and opaque organogels composed of 3D micellar networks when n is between 117 and 230. Those organogels could transform into thinning fluids composed of spherical micelles upon heating and regelling reversibly through cooling. Conformational interactions of PNMP-b-PMMA molecules in the organogel and solution analyzed using 1H NMR and 2D Noesy NMR reveal that the stretch of the solvophilic part PNMP plays an important role in the gel–sol transition process, and the thermoinduced sequencing variation in the isopropanol molecules as well. According to the interesting situ-forming gelling behaviors and the excellent biocompatibility of PNMP-b-PMMA components, this new family of block copolymers may offer some potential applications in transdermal drug delivery, biotechnology, nanomaterials development, and so forth.

Experimental Section

Materials

2-Cyanopropyl-2-dithiobenzoate (CPDB) was synthesized according to the reported method.50 2,2′-Azobisisobutyronitrile (AIBN, 99%) was purchased from Shanghai Hatech Co. Ltd. and recrystallized in ethanol twice. N-Hydroxyethyl pyrrolidone (98%, TCI), methacryloyl chloride, and methyl methacrylate (98%, Shanghai Hatech Co. Ltd.) were distilled under reduced pressure before use. Dimethylformamide (DMF, 99%, Shanghai Hatech Co. Ltd.) was distilled under reduced pressure, then mixed with 0.05 mol·L–1 of NaNO3 (99%, Shanghai Hatech Co. Ltd.), and filtered on 0.2 μm polytetrafluoroethylene filters for GPC. NMP was synthesized using the method described elsewhere.51 All other solvents and reagents were purchased from commercial sources and were used as received.

Synthesis of PNMP-b-PMMA Block Copolymer

PNMP-b-PMMA was synthesized according to the same procedure as reported previously38 (Scheme 1):

Scheme 1. Synthetic Route of PNMPm-b-PMMAn.

Scheme 1

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The typical synthetic procedure of PNMP macromolecular chain transfer agent (macro-CTA) is as follows: NMP (25.5 g, 129.44 mmol), CPDB (0.60 g, 2.70 mmol), AIBN (0.168 g, 1.03 mmol), and CH3CH2OH (50 mL) were charged into a 100 mL Schlenk flask capped with rubber septa. Subsequently, the homogenous solution was deoxygenated by purging with highly pure nitrogen gas for 30 min and then reacted at 60 °C for 10 h under stirring in a thermostatic oil bath. The monomer conversion was 93% as calculated from the 1H NMR spectrum using 1,3,5-trioxane as the internal standard. The crude product was diluted by dichloromethane and then poured into diethyl ether/petroleum ether mixture (v/v = 1:1) to precipitate at least twice. The final product was dried in a vacuum oven at 45 °C to give a pink powder. The mean polymerization degree m of PNMP macro-CTA agent was 37 as calculated from the 1H NMR spectrum (Figure S1) and GPC analysis: Mn = 8310 g·mol–1; Mw/Mn = 1.03 (Figure S2).

The PNMP-b-PMMA diblock copolymer was synthesized as follows: PNMP macro-CTA (2.0 g, 0.30 mmol), MMA (8.24 g, 82.40 mmol), AIBN (0.0183 g 0.11 mmol), and DMF (22 mL) were charged into a 50 mL Schlenk flask capped with rubber septa and then reacted and purified as mentioned earlier. The final product is a pink powder. The mean polymerization degree n of the PMMA segment was 189 as calculated from the 1H NMR spectrum (Figure S3) and GPC analysis: Mn = 31110 g·mol–1; Mw/Mn = 1.04 (Figure S2).

1H NMR and 2D Noesy NMR Spectra Measurements

1H NMR spectra were recorded on a 400 MHz Bruker-BioSpin spectrometer. The temperature-dependent 1H NMR experiment of 5 wt % PNMP37-b-PMMA151 in d8-isopropanol was performed in the temperature region between 25 and 55 °C with an interval of 5 °C, and the equilibrium time was 20 min at each temperature. Two-dimensional (2D) nuclear Overhauser effect spectrometry (Noesy) NMR measurements were recorded on the Bruker BioSpin GmbH NMR spectrometer with a proton frequency of 500.13 Hz at 25 and 55 °C, respectively. A 90° pulse width of 8.53 μs, a mixing time of 200 ms, a relaxation delay of 2 s, and an acquisition time of 205 ms were used. As many as 2048 complex points were collected and processed with a Lorentz-to-Gauss window function and zero filling in both dimensions to display data on a 2048 × 2048 2D matrix.

GPC Measurements

The GPC measurements were recorded at 35 °C using DMF (containing 0.05 M NaNO3) as an eluant at a flow rate of 1.0 mL·min–1. The column set consisted of two MZ-SD plus 5 μm columns (500 Å and Linear); a Wyatt Optilab DSP Interferometric refractometer and a Wyatt DAWN EOS multiangle laser light scattering detector with a helium–neon laser light source (λ = 685 nm), K5-flow cell, and a broad range of scattering angles from 45°–160° were used. The molecular weight and polydispersity data were determined using the Wyatt ASTRA software package. The refractive index increment of the polymer solution (dn/dc) was measured using an Optilab DSP refractometer at a wavelength of 685 nm.

Gel–Sol Transition Temperature Measurements

The gel–sol transition behaviors of PNMP-b-PMMA in isopropanol were studied by the tube tilting method52 as follows: each sample with a given concentration was prepared by dissolving the block copolymer in isopropanol through heating and stirring to form a clear and homogenous solution, and the gel was obtained by cooling the sample to ambient temperature and stored at 4 °C overnight. The vials, which were tightly sealed, were immersed in a water bath from 10 to 50 °C increasing by 1 °C per step. Each temperature was equilibrated for 15 min, and then the vials were inverted for 1 min to determine the condensed state. The state was regarded as a gel if the aqueous system in the vial did not flow within 1 min of inverting the vial.

Turbidity Measurements

The turbidity measurements were recorded using a UV–visible Tu-1901 spectrometer (Pgeneral, China) at 600 nm. The transmittance was measured between 0 and 70 °C through temperature-controlled heating and cooling cycles, and the sample was equilibrated for 30 min at each temperature before measurement.

Rheology Measurements

Rheology measurements were recorded on a RS 600 stress-controlled rheometer (TA Instruments) using a cone–plate geometry (diameter of 35 mm and a cone angle of 1°) at 20 °C. The distance between the sensor and the cone plate was adjusted to 52 μm for all measurements, and a solvent-trapping device was placed above the plate to minimize evaporation. The strain-sweeping experiments were performed at the fixed frequency (ω = 1 rad·s–1), and the frequency-sweeping measurements was taken at a constant shear strain of 1 Pa.

Light Scattering Measurements

SLS and DLS were performed on the Zetasizer ZEN 3600 (Malvern, U.K.) with a 173° back scattering angle using a He–Ne laser (λ = 633 nm). The sample was filtered through a 0.22 μm filter membrane to remove any interfering dust particles and equilibrated for 30 min before each measurement.

Electron Microscopy Measurements

The SEM experiments were performed on a Zeiss Sigma field-emission scanning electron microscope. The samples were lyophilized before the SEM observation. Before the examination, the solid sample was placed on a double-sided sticky carbon tape mounted on aluminum sample holders, and then it was sputter-coated with a thin layer of gold using an SCD 005 cool sputter coater (Bal-Tec) at 30 mA and ∼7 Pa for 80 s.

cryo-TEM was performed as follows: A small drop of the sample (3–5 μL) was deposited on the surface of a TEM copper grid covered by a holey carbon film at 30 °C. After blotting away the excess solution to form a thin liquid film, the grid was immediately plunged into liquid ethane cooled by liquid nitrogen (−175 °C). The specimens were maintained at approximately −173 °C and imaged using a transmission electron microscope Tecnai G20 TWIN at an accelerating voltage of 200 kV under low-dose conditions.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (NSFC 21273165 and 21573164).

Supporting Information Available

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.6b00327.

  • Methods for the calculation of the polymerization degree m and n of PNMPm and PNMPm-b-PMMAn from 1H NMR result, GPC and 1H NMR results of PNMPm and PNMPm-b-PMMAn, methods for the calculation of polymerization degree m and from 1H NMR result, the micellization behaviors of PNMPm-b-PMMAn in diluted isopropanol solution, the appearance of 5 wt % PNMPm-b-PMMAn in isopropanol at different temperatures, and the micellar size distribution of 5 wt % PNMP37-b-PMMA117 in isopropanol at 30 °C obtained from the cryo-TEM image (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao6b00327_si_001.pdf (767.9KB, pdf)

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