Well-Controlled Formation of Nanofibers and Double Wall Vesicles

Mar 12, 2009 - Electrostatic-Assisted Assembly of a Couple of Star Polyelectrolytes- ... as fiber bundles and double wall vesicles in water by adjusti...
0 downloads 0 Views 2MB Size
Download PDF
5126

J. Phys. Chem. C 2009, 113, 5126–5132

Well-Controlled Formation of Nanofibers and Double Wall Vesicles through the Electrostatic-Assisted Assembly of a Couple of Star Polyelectrolytes-Complementary Jianhua Ding, Li Wang,* Haojie Yu, Jia Huo, Qingquan Liu, and Anguo Xiao State Key Laboratory of Chemical Engineering, Department of Chemical and Biochemical Engineering, Zhejiang UniVersity, Hangzhou 310027, China ReceiVed: December 8, 2008; ReVised Manuscript ReceiVed: February 17, 2009

A series of water-soluble hexa-armed cationic star polyelectrolytes and anionic star polyelectrolytes with a hexafunctional cyclotriphosphazene derivative core were synthesized. The self-assembly behaviors of these complementary star polyelectrolyte pairs in water in the effect of electrostatic interaction were investigated. It was found that the complementary star polyelectrolyte pairs system could form various morphologies such as fiber bundles and double wall vesicles in water by adjusting molecular weight, polymer concentration, the matching degree of star polyelectrolyte pairs, and the preparation conditions of the self-assembly solvents. The self-assembly mechanisms for the formation of nanofibers and double wall vesicles were discussed. Introduction

Experimental Section

Biomacromolecules are actually polyelectrolytes; for instance, polypeptides from which many organs are constructed are polyelectrolytes.1-5 Some biomacromolecules are obtained through self-assembly of polyelectrolytes.6-9 Polyelectrolytes can self-assemble in water under gentle conditions, and the aggregates formed can be employed in encapsulation of biologically relevant compounds such as proteins.10-12 Furthermore, polyelectrolytes can self-assemble to form vesicles and the shell of the vesicles with the ability of permeability of hydrophilic solutes, which is a very important property for which the vesicles can be used in the field of microreactor and artificial cells.13,14 So the investigation of self-assembling of artificial polyelectrolytes is of great interest for simulating biological systems.15-17 In particular, the preparation of the nanofibers and double wall vesicles is a research hot point because usually nanofiber and double wall vesicles are basic elements for biological systems.

Materials. Hexachlorocyclotriphosphazene was recrystallized from dry hexane and was sublimated twice before use. 4-Hydroxybenzaldehyde, tert-butyl methacrylate, and 2-(dimethylamino) ethyl methacrylate were purchased from Acros organics. tert-Butyl methacrylate and 2-(dimethylamino) ethyl methacrylate were washed with an aqueous solution of sodium hydroxide (NaOH) (5 wt %) three times and then with water until neutralization. After being dried with anhydrous magnesium sulfate, the tert-butyl methacrylate was distilled under reduced pressure. Sodium borohydride was purchased from Shanghai Chemical Reagents Corp. 2-Bromoisobutyryl bromide was purchased from Sigma-Aldrich and was used directly. Tetrahydrofuran (THF) was refluxed over potassium and distilled in argon atmosphere. Triethylamine (Et3N) was distilled over KOH. Anisole was treated with baked molecular sieves. Copper(I) (CuCl, AR grade) was purified by stirring in acetic acid, washing with methanol, and then drying under reduced pressure. 2,2′Bipyridyl (bpy), AR grade, was used as obtained from the Shanghai No. 1 Chemical reagent factory. 1,1,3,3,5,5-Hexakis (4-(2-bromoisobutyryloxymethyl)-phenoxy) cyclotriphosphazene (HBPC) was prepared according to the literature.23 Other reagents were analytical-grade and were used as received without further purification. Synthesis of Star Poly(tert-butyl methacrylate) (Star(PtBMA)6). 24-26 The polymerization was carried out at 90 °C with the feed ratio of [monomer]/[HBPC]/[CuCl]/[bpy] ) 600/ 1/6/12 (molar ratio). A typical procedure is as follows: CuCl, bpy, HBPC, and tert-butyl methacrylate were successively added into a 10 mL glass tube, and then a certain amount of anisole was added to the tube by syringe. The heterogeneous mixture was cycled between vacuum and nitrogen four times to remove air. The tube was sealed under vacuum and then immersed in an oil bath at the preset temperature. After the reaction was carried out for a prescribed time, the tube was rapidly cooled to room temperature with ice water, and the polymer solution in THF was passed through a short column of neutral alumina to remove the copper salts. The polymer was precipitated from an excess of ethanol/water (v/v ) 70/30) mixture, filtered, and dried at 50 °C under vacuum to constant weight.

Star polyelectrolytes with a hexafunctional crystalline cyclotriphosphazene derivative core exhibit special three-dimensional shape, which is explained in terms of a model consisting of six polymer chains arranged approximately perpendicular to the cyclotriphosphazene ring.18-22 These star polyelectrolytes have the ability to self-assemble in solution, forming a range of different morphologies as their linear polymer counterparts. In the present study, a series of water-soluble hexa-armed cationic star polyelectrolytes and anionic star polyelectrolytes with a hexafunctional cyclotriphosphazene derivative core were synthesized. The self-assembly behaviors of these complementary star polyelectrolyte pairs in water in the effect of electrostatic interaction were investigated. The synthesis of these star polyelectrolytes (Figure 1) is shown in Scheme 1. Because of the special properties and high structural symmetry of star polyelectrolytes, these hexa-armed complementary star polyelectrolyte pairs show unique self-assembly behaviors, and many aggregates with special morphology and structure were successfully prepared. * Corresponding author. Telephone: +86-571-8795-3200. Fax: +86-5718795-1612. E-mail: [email protected].

10.1021/jp810782f CCC: $40.75  2009 American Chemical Society Published on Web 03/12/2009

Formation of Nanofibers and Double Wall Vesicles

J. Phys. Chem. C, Vol. 113, No. 13, 2009 5127

Figure 1. The structure of cationic star polyelectrolyte and anionic star polyelectrolyte.

SCHEME 1: Synthesis Procedure of Star Polyelectrolytes-Complementary

Synthesis of Star Poly(methacrylic acid) (Star-(PMAA)6). The hydrolysis of tert-butyl side groups on the Star(PtBMA)6 to acrylic acid was carried out according to the literature.27 0.52 mL (7.035 mmol) of trifluoroacetic acid was added dropwise to a CH2Cl2 solution of Star-(PtBMA)6 (200 mg of Star-(PtBMA)6 containing 1.406 mmol of tert-butyl 26,27

groups in 6.0 mL of CH2Cl2). The reaction mixture was stirred at room temperature for 12 h. After hydrolysis, the solution became cloudy with observed precipitation, indicating the formation of carboxyl side groups. The resultant star polymer was filtered and washed with THF three times, and then dried at 50 °C under vacuum to constant weight.

5128 J. Phys. Chem. C, Vol. 113, No. 13, 2009 Synthesis of Star Poly(2-(dimethylamino)ethyl methacrylate) (Star-(PDMAEMA)6). 28 The polymerization was carried out at 90 °C with a feed ratio of [monomer]/[HBPC]/[CuCl]/ [bpy] ) 600/1/6/12 (molar ratio). A typical procedure is described as follows. Into a 10 mL glass tube were added CuCl, bpy, and HBPC successively, and then a certain amount of 2-(dimethylamino)ethyl methacrylate and anisole was added to the tube through syringe. The heterogeneous mixture was cycled between vacuum and nitrogen four times to remove gas. The tube was sealed under vacuum and then immersed in an oil bath at the presetting temperature. After the reaction was carried out for a prescribed time, the tube was rapidly cooled to room temperature with ice water, and the polymer solution in THF was passed through a short column of neutral alumina to remove the copper salts. The polymer was precipitated from an excess of hexane three times, filtered, and dried at 50 °C under vacuum to constant weight. Synthesis of Star Poly(2-(dimethy ethyl ammonium iodide) ethyl methacrylate)6 (Star-(PDME AIEMA)6). 29 The quaternization of dimethyamino groups in Star-(PDMAEMA)6 to quarterized nitrogen was carried out following a literature procedure. Ethyl iodide (2 times excess to the dimethyamino groups, 0.206 mL, 2.544 mmol) was added dropwise to a solution of Star-(PDMAEMA)6 (200 mg, 1.272 mmol dimethyamino groups) in 6.0 mL of methanol. The reaction mixture was stirred at room temperature for 12 h, and the polymer was precipitated from an excess of tetrahydrofuran three times. The resultant star polymer was filtered and washed with THF three times, and then dried at 50 °C under vacuum to constant weight. Self-Assembly of Star Polyelectrolytes. Extremely dilute solutions of complexes between star polyelectrolytes containing 0.20 wt % Star-(PMAA)6 were prepared by dissolving a certain amount of Star-(PMAA)6 and a certain amount of Star(PDMEAIEMA)6 in water at room temperature (25 °C), followed by sonication for 1 h. Samples for TEM measurement were prepared by aerosol spraying a dilute micelle solution (ca. 10 µL) onto 200-mesh gilder copper TEM grids. The samples were air-dried before introduction into TEM. The morphology and structure of the prepared samples were examined with TEM. Characterization. 1H NMR was obtained from a 400 MHz AVANCE NMR spectrometer (model DMX400). For protons, the chemical shifts were relative to tetramethylsilane at δ ) 0 ppm. The molecular weight and molecular weight distribution were determined by gel permeation chromatography (GPC) with a laser scattering detector. The eluent was THF at a flow rate of 1.0 mL/min, and calibrations were narrow-distribution polystyrene standards. TEM micrographs were obtained on a JEOL model 1200EX instrument operated at an accelerating voltage at 160 kV. Results and Discussion Synthesis of Star Polyelectrolytes-Complementary. The synthesis routes of star polyelectrolytes-complementary were depicted in Scheme 1.26 First, hexa-armed Star-(PtBMA)6 with a cyclotriphosphazene core was prepared by atom transfer radical polymerization (ATRP) of tert-butyl methacrylate with HBPC as initiator, and then anionic star polyelectrolyte Star(PMAA)6 was obtained after hydrolysis of the tert-butyl moieties in the polymer chain of Star-(PtBMA)6. Cationic star polyelectrolyte Star-(PDMEAIEMA)6 also prepared by two steps and the synthesis procedure was shown in Scheme 1. Precursor hexaarmed Star-(PDMAEMA)6 with a cyclotriphosphazene core was prepared by the atom transfer radical polymerization (ATRP) and core-first technique; after quaternization of dimethyamino

Ding et al. TABLE 1: Molecular Weight and Molecular Weight Distribution of Star-(PtBMA)6 and Star-(PDMAEMA)6 polymera

Mna

Mw/Mna

Star-(PtBMA25b)6 Star-(PtBMA36)6 Star-(PDMAEMA26)6 Star-(PDMAEMA35)6

2.26 × 104 3.07 × 104 2.64 × 104 3.29 × 104

1.27 1.24 1.25 1.26

a Mn(GPC) and Mw/Mn were determined by GPC analysis with polystyrene standards; THF was used as eluent. b The average number of repeating units per arm.

groups in the polymer chain of precursor, cationic star polyelectrolyte Star-(PDMEAIEMA)6 was prepared. Characterization of Precursor Star-(PtBMA)6 and Star(PDMAEMA)6. The chemical structures and molecular weight of the prepared precursors were characterized by 1H NMR analysis and GPC. The 1H NMR spectrum of Star-(PtBMA)6 showed the following shifts (400 MHz, CDCl3): 7.20-6.91 (4H in -C6H4-), 4.98 (2H in -CH2O-), 2.10-1.70 (2H in -CH2-C-), 1.40 (12H in -COOC(CH3)3), 1.20-0.82 (3H in -CH2-C(CH3)-), 1.12 (6H in -C(CH3)2-).26 The 1H NMR spectrum of Star-(PDMAEMA)6 showed the following shifts (400 MHz, CDCl3): 7.20-6.81 (4H in -C6H4-), 4.98 (2H in -CH2O-), 4.00 (2H in -COOCH2-), 2.55 (2H in -COOCH2CH2-), 2.22 (6H in -N(CH3)2), 1.98-1.70 (2H in -CH2-C-), 1.18 (6H in -C(CH3)2-), 1.12-0.79 (3H in -CH2-C(CH3)-). The molecular weights of Star-(PtBMA)6 and Star-(PDMAEMA)6 are shown in Table 1. Characterization of Star Polyelectrolytes-Complementary. The chemical structures of the prepared star polyelectrolytescomplementary were characterized by 1H NMR. The 1H NMR spectrum of Star-(PMAA)6 showed the following shifts (400 MHz, CDCl3): 10.50-12.00 (1H in -COOH), 7.25-6.92 (4H in -C6H4-), 4.98 (2H in -CH2O-), 2.10-1.25 (2H in -CH2-C-), 1.15-0.80 (3H in -CH2-C(CH3)-), 1.12 (6H in -C(CH3)2-).26 The 1H NMR spectrum of Star-(PDMEAIEMA)6 showed the following shifts (400 MHz, CDCl3): 7.95-6.81 (4H in -C6H4-), 5.72 (2H in -CH2O-), 4.42-3.70 (2H in -COOCH2CH2-), 3.60 (2H in -COOCH2-), 3.22 (6H in -N(CH3)2CH2CH3), 3.18 (2H in -N(CH3)2CH2CH3), 1.80-1.70 (2H in -CH2-C-), 1.25 (3H in -N(CH3)2CH2CH3), 1.15-0.79 (3H in -CH2-C(CH3)- and 6H in -C(CH3)2-). The 1H NMR spectra showed that Star-(PMAA)6 and Star(PDMEAIEMA)6 have been prepared.30 Self-Assembly Behaviors of Star Polyelectrolytes-Complementary. By blending a couple of complementary star polyelectrolytes, polyion chains with opposite charges in star polyelectrolytes will attract and complex with each other to form star polyelectrolyte complex aggregates. Furthermore, the polyion chains in star polyelectrolyte are expansible or stretchable due to the strong electrostatic repulsion between charged segments, and one star polyelectrolyte molecular possesses many long polyion chains, so the complexation of star polyelectrolytes with complementary charges is easy to achieve.31 Generally, the self-assembly of star polyelectrolytes with opposite charges can be divided into three processes.32 First, star polyelectrolyte molecules with opposite charges attract through diffusion. Second, the polyion chains with opposite charges in star polyelectrolyte attract through the effect of electrostatic interaction and diffusion. Last, two adjacent polyion chains with opposite charges complex with each other through the charge neutralization process. So, the self-assembly behaviors of star polyelectrolytes were greatly influenced by several factors, such as star polyelectrolyte concentration, molecular

Formation of Nanofibers and Double Wall Vesicles

J. Phys. Chem. C, Vol. 113, No. 13, 2009 5129

Figure 2. TEM images of the self-assembly aggregates from Star-(PMAA)6-Star-(PDMEAIEMA)6 with different lengths of polymer arm at Star-(PMAA)6 concentrations of 0.2 wt % and H2O as solvent. Star-(PMAA25)6-Star-(PDMEAIEMA26)6 (A1, A2), and Star-(PMAA36)6-Star(PDMEAIEMA35)6 (B1, B2).

weight and volume of star polyelectrolyte, ionic strength, and the matching degree of star polyelectrolyte pair. To investigate these behaviors, we have prepared a series of anionic star poly(methacrylic acid) (Star-(PMAA)6) and cationic star poly(2(dimethy ethyl ammonium iodide)ethyl methacrylate) (Star(PDMEAIEMA)6), and these star polyelectrolytes prepared can be divided into two groups of complementary star polyelectrolyte pairs. When water was used as the solvent, the length of the polyion chains was a versatile parameter with which to adjust the selfassembly behaviors of complementary star polyelectrolyte pairs with matched length of polyion chains. The self-assembly behaviors of two group of complementary star polyelectrolyte pairs Star-(PMAA)6-Star-(PDMEAIEMA)6 with matched length of polyion chains were investigated. It was found that long fibers were formed by the self-assembly of complementary star polyelectrolyte pairs at the fixed Star-(PMAA)6 concentration of 0.2 wt %. The morphologies of the resultant aggregates were observed by transmission electron microscopy (TEM). The TEM images for the aggregates formed by the matched star polyelectrolyte pairs Star-(PMAA)6-Star-(PDMEAIEMA)6 system with different lengths of polyion chains are shown in Figure 2. For the Star-(PMAA25)6-Star-(PDMEAIEMA26)6 system with shorter matched polyion chains, long fibers with diameter of several nanometers and an average length of 4 µm were formed, and the fibers tend to attract to form fiber bundles (Figure 2A1, A2). Fibers with diameter of several nanometers and an average length of 2 µm were formed by the Star-(PMAA36)6-Star(PDMEAIEMA35)6 system, which possesses longer matched polyion chains, and the fibers formed also tend to aggregate together to form fiber bundles (Figure 2B1, B2). The Star-(PMAA)6-Star-(PDMEAIEMA)6 system possesses equal number of carboxyl groups and quaternary amino groups, respectively, and the carboxyl groups in polymer chains of Star-

(PMAA)6 can complex with the quaternary amino groups of Star-(PDMEAIEMA)6 under electrostatic interactions.33,34 One star polyelectrolyte molecular possesses many polyion chains, and the complexation of Star-(PMAA)6 with Star-(PDMEAIEMA)6 in water results in the formation of multimolecular associate. Star polyelectrolytes with a cyclotriphosphazene exhibit special three-dimensional shape, which are explained in terms of a model consisting of six polymer chains arranged approximately perpendicular to the cyclotriphosphazene ring, and the polyion chains in star polyelectrolyte are expansible or stretchable due to the strong electrostatic repulsion between charged segments. So, under a high star polyelectrolyte concentration, the number of polymer molecules in solution was larger, and the polyelectrolyte molecule adopts to form a structure with small volume and the molecule can be regarded as a long cylinder. On the basis of the self-assembly morphologies of the matched star polyelectrolyte pairs Star-(PMAA)6Star-(PDMEAIEMA)6 system and the analysis above, we propose a model for the self-assembly behaviors of the matched star polyelectrolyte pairs system (Figure 3). The Star-(PMAA25)6-Star-(PDMEAIEMA26)6 system possesses shorter polyion chains and smaller volume; at the Star(PMAA25)6 concentration of 0.2 wt %, two types of star polyelectrolytes can be considered as a long cylinder with charges in the surface. These star polyelectrolytes diffuse in solution, and when the distance of a couple of complementary star polyelectrolytes is decreased to a certain degree, the polyion chains in these star polyelectrolytes will complex with counter polyion chains under electrostatic interaction. The charge neutralization process leads to the Star-(PMAA25)6 molecule joined with the Star-(PDMEAIEMA26)6 molecule to form a long fiber. Polyelectrolyte concentration also plays an important role in the self-assembly behavior of the complementary star polyelectrolyte pairs with matched length of polyion chains. Generally,

5130 J. Phys. Chem. C, Vol. 113, No. 13, 2009

Ding et al.

Figure 3. Possible model for the formation of fiber bundles. Green, cyclotriphosphazene core; pink, PMAA; blue, PDMEAIEMA.

Figure 4. TEM images of the self-assembly aggregates from Star-(PMAA)6-Star-(PDMEAIEMA)6 with different lengths of polymer arm at Star-(PMAA)6 concentrations of 0.1 wt % and H2O as solvent. Star-(PMAA25)6-Star-(PDMEAIEMA26)6 (A1, A2, A3, A4), and Star-(PMAA36)6-Star(PDMEAIEMA35)6 (B1, B2, B3).

a strong interaction between solutes exists in a concentrated solution, and a stronger solvent effect occurs in a dilute solution. The TEM images for the aggregates formed by the matched star polyelectrolyte pairs Star-(PMAA)6-Star-(PDMEAIEMA)6 system with different lengths of polyion chains at a fixed Star(PMAA)6 concentration of 0.1 wt % are shown in Figure 4. For the Star-(PMAA25)6-Star-(PDMEAIEMA26)6 system, which possesses shorter matched polyion chains, short fibers with diameter of about 20 nm and an average length of 500 nm were formed, and the fibers have a good dispersibility and have a uniform length (Figure 4A1, A2, A3). Fibers with diameter of about 40 nm and a broad length distribution of 300-700 nm were formed by the Star-(PMAA36)6-Star-(PDMEAIEMA35)6 system, which possesses longer matched polyion chains. The fibers formed also possess a good dispersibility (Figure 4B1, B2, B3).

At a low star polyelectrolyte concentration, the number of polymer molecules in solution was small, the polyelectrolyte molecule tends to form a structure with larger volume, and the whole molecule can be regarded as a disk. On the basis of the self-assembly morphologies of the matched star polyelectrolyte pairs Star-(PMAA)6-Star-(PDMEAIEMA)6 system, we propose a model for the self-assembly behaviors of the matched star polyelectrolyte pairs system, and the model is shown in Figure 5. The Star-(PMAA25)6-Star-(PDMEAIEMA26)6 system possesses shorter polyion chains and smaller volume; at the Star(PMAA25)6 concentration of 0.1 wt %, two types of star polyelectrolytes can be considered as a disk with its two faces full of charges. These star polyelectrolytes diffuse in solution, and when the distance of two star polyelectrolyte molecules with opposite charges is decreased to a certain degree, the face

Formation of Nanofibers and Double Wall Vesicles

J. Phys. Chem. C, Vol. 113, No. 13, 2009 5131

Figure 5. Possible model for the formation of short fibers. Green, cyclotriphosphazene core; pink, PMAA; blue, PDMEAIEMA.

of the disk will complex with the face of counter disk under electrostatic interaction. The charge neutralization process leads to the Star-(PMAA25)6 molecule joining with the Star-(PDMEAIEMA26)6 molecule face by face to form a short fiber. At a low star polyelectrolyte concentration, the diffusion and regular arrangement of star polyelectrolytes is relatively easy, and almost all of the polyion chains complex with counter polyion chains. The short fibers formed have few defects, and there are almost no free charges in the surface of the fibers, so the fiber formed has a good dispersibility. The Star-(PMAA36)6-Star-(PDMEAIEMA35)6 system possesses longer polyion chains and larger volume, which means that the diffusion and regular arrangement of star polyelectrolyte molecules become more difficult. The average number of star polyelectrolyte molecules joining together to form fibers decreases, so the fibers formed have a shorter length and a broader length distribution. The fibers formed have few defects, which grant fibers with good dispersibility, but in some positions the arrangement of star polyelectrolyte molecules becomes irregular and the diameter of fibers formed becomes nonuniform. It is well-known that the self-assembly behaviors of complementary star polyelectrolyte pairs were greatly influenced by the matching degree of star polyelectrolyte pairs. To study the influence of the matching degree of star polyelectrolyte pairs on the self-assembly behaviors of the complementary star polyelectrolyte pairs, the self-assembly behaviors of the Star(PMAA36)6-Star-(PDMEAIEMA26)6 system, which possesses unmatched polyion chains and with different Star-(PMAA)6 concentration, were investigated. The Star-(PMAA36)6-Star-(PDMEAIEMA26)6 system can self-assemble to form double wall vesicles with different dimensions in H2O. The TEM images for the aggregates formed by the unmatched star polyelectrolyte pairs Star-(PMAA36)6-Star(PDMEAIEMA26)6 system at different Star-(PMAA)6 concentrations are shown in Figure 6. Double wall vesicles with an average diameter of 300 nm were formed through the selfassembly of the Star-(PMAA36)6-Star-(PDMEAIEMA26)6 system at the Star-(PMAA36)6 concentration of 0.1 wt % (Figure 6A1, A2). The double wall vesicles formed tend to aggregate together, and several vesicles attract to form a honeycomb-like aggregate. As the Star-(PMAA36)6 concentration increased to 0.2 wt %, honeycomb-like aggregates with larger dimension were formed and the number of aggregates increased, but single double wall vesicle disappeared, as all single vesicles aggregated together to form honeycomb-like aggregates and single vesicles with an average diameter of 500 nm (Figure 6B1, B2). In the Star-(PMAA36)6-Star-(PDMEAIEMA26)6 system, anionic star polyelectrolytes have longer polyion chains than do

Figure 6. TEM images of the self-assembly aggregates from Star(PMAA36)6-Star-(PDMEAIEMA26)6 at different Star-(PMAA36)6 concentrations in H2O. Star-(PMAA36)6 concentrations: 0.1 wt % (A1, A2), and 0.2 wt % (B1, B2).

Figure 7. Proposed molecular packing models for the self-assembling of Star-(PMAA36)6-Star-(PDMEAIEMA26)6 at various concentrations.

cationic star polyelectrolytes. So, to ensure the number of carboxyl groups is equal to the number of quaternary amino groups, the number of Star-(PMAA36)6 molecules is less than the number of Star-(PDMEAIEMA26)6 molecules in the system, and one Star-(PMAA36)6 molecular can be complexed with more than one Star-(PDMEAIEMA26)6 molecules. Therefore, the selfassembly behaviors of the Star-(PMAA36)6-Star-(PDMEAIEMA26)6 system are similar to those of Star-(PDMEAIEMA)6. With the interactions of electrostatic and hydrophilic-hydrophobic and the effect of the core, the Star-(PMAA36)6-Star-(PDMEAIEMA26)6 system can self-assemble to form vesicle aggregates with large dimension. On the basis of the aggregates shown in Figure 6, we proposed a possible self-assembly mechanism of the Star-(PMAA36)6-Star-(PDMEAIEMA26)6 system to form honeycomb-like aggregates as shown in Figure 7. Conclusions In conclusion, a series of complementary star polyelectrolyte pairs with a cyclotriphosphazene derivative core were successfully synthesized, and the self-assembly behaviors of complementary star polyelectrolyte pairs in water were investigated carefully. It was found that the complementary star polyelectrolyte pairs system could form various morphologies such as fiber bundles and double wall vesicles in water by adjusting molecular weight, polymer concentration, the matching degree of star polyelectrolyte pairs, and the preparation conditions of

5132 J. Phys. Chem. C, Vol. 113, No. 13, 2009 the self-assembly solvents. The resulting aggregates with many different morphologies possess special structures and show new potential applications in the field of biomaterials and nanotechnology, etc. References and Notes (1) Ko¨tz, J.; Kosmella, S.; Beitz, T. Prog. Polym. Sci. 2001, 26, 1199– 1232. (2) Yap, H. P.; Quinn, J. F.; Johnston, A. P. R.; Caruso, F. Macromolecules 2007, 40, 7581–7589. (3) Sfika, V.; Tsitsilianis, C. Macromolecules 2003, 36, 4983–4988. (4) Kataoka, K.; Togawa, H.; Harada, A.; Yasugi, K.; Matsumoto, T.; Katayose, S. Macromolecules 1996, 29, 8556–8557. (5) Lukanoff, B.; Burmester, G. R.; Dautzenberg, H. Biomaterials 1996, 17, 1049–1051. (6) Tao, X.; Li, J.; Mo¨hwald, H. Chem.-Eur. J. 2004, 14, 3397–3403. (7) Yao, X.; Chen, D.; Jiang, M. Macromolecules 2004, 37, 4211– 4217. (8) Lysenko, E. A.; Bronich, T. K.; Slonkina, E. V.; Eisenberg, A.; Kabanov, V. A.; Kabanov, A. V. Macromolecules 2002, 35, 6351–6361. (9) Yang, H.; Fung, S.-Y.; Pritzker, M.; Chen, P. J. Am. Chem. Soc. 2007, 129, 12200–12210. (10) Jahnke, E.; Severin, N.; Kreutzkamp, P.; Rabe, J. P.; Frauenrath, H. AdV. Mater. 2008, 20, 409–414. (11) Iatrou, H.; Frielinghaus, H.; Hanski, S.; Ferderigos, N.; Ruokolainen, J.; Ikkala, O.; Richter, D.; Mays, J.; Hadjichristidis, N. Biomacromolecules 2007, 8, 2173–2181. (12) Yasuhiko, T.; Ksisuke, Y.; Susumu, M.; Izumi, N.; Haruhiko, K.; Ikuo, A.; Makoto, T.; Yoshito, I. Biomaterials 1998, 19, 807–815. (13) Khopade, A. J.; Caruso, F. Langmuir 2003, 19, 6219–6225. (14) Khopade, A. J.; Caruso, F. Nano Lett. 2002, 2, 415–418. (15) Murthy, V. S.; Cha, J. N.; Stucky, G. D.; Wong, M. S. J. Am. Chem. Soc. 2004, 126, 5292–5299. (16) Mchenna, B. J.; Birkedal, H.; Bartl, M. H.; Deming, T. J.; Stucky, G. D. Angew. Chem., Int. Ed. 2004, 43, 5652–5655.

Ding et al. (17) Hu, Y.; Jiang, X. Q.; Ding, Y.; Chen, Q.; Yang, C. Z. AdV. Mater. 2004, 16, 933–937. (18) Joaquı´n, B.; Josefina, J.; Antonio, L.; Luis, O.; Sonia, P.; Jose´, L. S. Chem. Mater. 2006, 18, 5437–5445. (19) Kenzo, I.; Akiko, M.; Tomoyuki, I. J. Am. Chem. Soc. 1997, 119, 6191–6192. (20) Rele, S. M.; Cui, W.; Wang, L.; Hou, S.; Barr-Zarse, G.; Tatton, D.; Gnanou, Y.; Esko, J. D.; Chaikof, E. L. J. Am. Chem. Soc. 2005, 127, 10132–10133. (21) Reed, N. N.; Janda, K. D. Org. Lett. 2000, 2, 1311–1313. (22) Bertani, R.; Chaux, F.; Gleria, M.; Metrangolo, P.; Milani, R.; Pilati, T.; Resnati, G.; Sansotera, M.; Venzo, A. Inorg. Chim. Acta 2007, 360, 1191–1199. (23) Matyjaszewski, K.; Miller, P. J.; Pyun, J.; Kickelbick, G.; Diamanti, S. Macromolecules 1999, 32, 6526–6535. (24) Zhang, X.; Xia, J.; Matyjaszewski, K. Macromolecules 2000, 33, 2340–2345. (25) Abraham, S.; Ha, C.-S.; Kim, I. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 6367–6378. (26) Ding, J.; Wang, L.; Yu, H.; Huo, J.; Liu, Q.; Xiao, A. J. Phys. Chem. C. 2009, 113, 3471–3477. (27) Ma, Q.; Wooley, K. L. J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 4805–4820. (28) Cai, Y.; Armes, S. P. Macromolecules 2005, 38, 271–279. (29) Maeda, Y.; Mochiduki, H.; Ikeda, I. Macromol. Rapid Commun. 2004, 25, 1330–1334. (30) Ding, J. H. Master Thesis, Zhejiang University, 2008. (31) Cao, Y.; Shen, X. C.; Chen, Y.; Guo, J.; Chen, Q.; Jiang, X. Q. Biomacromolecules 2005, 6, 2189–2196. (32) Hu, Y.; Jiang, X. Q.; Ding, Y.; Chen, Q.; Yang, C. Z. Biomaterials 2002, 23, 3193–3201. (33) Fo¨rster, S.; Hermsdorf, N.; Bo¨ttcher, C.; Lindner, P. Macromolecules 2002, 35, 4096. (34) Mori, H.; Mu¨ller, A. H. E.; Klee, J. E. J. Am. Chem. Soc. 2003, 125, 3712–3713.

JP810782F