microemulsions

Polymer 53 (2012) 1093e1097

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Preparation of poly(methyl methacrylate) by ATRP using initiators for continuous activator regeneration (ICAR) in ionic liquid/microemulsions Guoxiang Wang a, *, Mang Lu b, Hu Wu a a b

College of Chemistry and Chemical Engineering, Hunan Institute of Science and Technology, Yueyang 414006, Hunan Province, China School of Materials Science and Engineering, Jingdezhen Ceramic Institute, Jingdezhen 333403, Jiangxi Province, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 18 November 2011 Received in revised form 13 January 2012 Accepted 21 January 2012 Available online 27 January 2012

In this study, we reported the synthesis of poly(methyl methacrylate) (PMMA) polymers via initiators for continuous activator regeneration atom transfer radical polymerization using CCl4 as initiator, FeCl3$6H2O/hexamethylene tetramine as catalyst complex, and 2,20 -azobis(isobutyronitrile) (AIBN) as reducing agent. The polymerization was conducted at 60  C in the ionic liquid based microemulsion with hexadecyl trimethyl ammonium bromide (CTAB) as surfactant. Kinetics experimental results showed that the polymerization proceeded in a controlled/‘living’ process. The effects of the molar ratio of [CCl4]/ [FeCl3$6H2O], the concentration of AIBN, temperature and the concentration of CTAB on the polymerization was investigated. The effect of CTAB concentration on the resulting PMMA particle size was also investigated. The obtained polymer was characterized by proton nuclear magnetic resonance and gel permeation chromatography. The living characteristics were demonstrated by chain extension experiment. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Methyl methacrylate Living polymerization Ionic liquid based microemulsion

1. Introduction Controlled/living radical polymerization (CLRP) provides a polymerization technique for production of well-defined polymers with narrow molecular weight distributions (MWD) in the 1995s [1,2]. During the past decades, many CLRPs have been developed. Among them, atom transfer radical polymerization (ATRP) has been demonstrated to be one of the most powerful, versatile, simple, and inexpensive living polymerization techniques. ATRP is mediated by transition metal catalyst and establishes a dynamic equilibrium between the activator and deactivator. ATRP has been applied in a variety of monomers under different conditions. However, traditional ATRP has some limitation due to high concentration of catalyst used. In order to overcome this drawback, some improved ATRP techniques have been developed, including initiators for continuous activator regeneration (ICAR) [3e5], and activator regenerated by electron transfer (ARGET) [6e8]. In a typical ICAR ATRP system, a classic thermal radical initiator (such as 2,20 -azobis(isobutyronitrile), AIBN) was used as reducing agent, and higher-oxidation-state transition metal (deactivator) was reduced to lower-oxidation-state transition metal (activator)

* Corresponding author. Tel.: þ86 730 8648525; fax: þ86 730 8640122. E-mail address: [email protected] (G. Wang). 0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2012.01.042

(Scheme 1). Kinetic experimental results have shown that the polymerization rate was depended on the rate of the radicals generated in ICAR ATRP [9]. ATRP has also been applied in emulsion polymerization [10e12], miniemulsion polymerization [13e15], suspension polymerization [16], and microemulsion polymerization [17e19]. Unlike other emulsion polymerization, microemulsions are thermodynamically stable, transparent or translucent, and homogeneous systems with a particle size of about 50e100 Å. It provides an important advantage over the traditional or coarse emulsions that are only kinematically stable upon significant agitation [20]. Recently, a novel procedure named activator generated by electron transfer (AGET ATRP) has been applied to microemulsion polymerization using a continuous “two-step” procedure [19]. In AGET ATRP, low surfactant amount was used and a controlled microemulsion was obtained. However, the concentration of catalyst remained higher. As “green” solvents, ionic liquids have been successfully used in polymer synthesis [21,22] mainly due to their very low volatility and the enhancement of radical polymerizations, as compared with those carried out in more conventional reaction media. A number of monomers have been successfully polymerized in a controlled fashion in ionic liquids, including methyl methacrylate (MMA) [23,24], acrylates [25,26]. In recent years, ionic liquids based microemulsions have attracted significant attention due to combining the advantages of ionic liquid and microemulsion [27e29]. As a new medium, ionic liquid based microemulsions have

1094

G. Wang et al. / Polymer 53 (2012) 1093e1097

Rn X MtnX2/L (ATRP initiator)

kact Mtn+1X3/L kdeact

Rn M kp kt

Rn Rn AIBN 2I (classic thermal initiator) (X=Br, Cl, L=ligand) (AIBN=azobis(isobutyronitrile)) I

X

Scheme 1. Proposed mechanism of ICAR ATRP.

been applied in organic synthesis [30], biocatalysis [31], nanomaterials [32] and polymerization [33]. Very recently, MMA was polymerized using copper-mediated AGET ATRP in ionic liquid based microemulsion at the relatively low temperature of 30  C [34]. In this study, the average diameter particle size was 5 nm and MWD was 1.20e1.40. The major drawback of AGET ATRP is higher concentration of catalyst used than that in ICAR ATRP. Many transition metal complexes were used in ATRP. In view of standpoint of environmentally friendly polymerization process, iron complexes were ideal catalysts due to their lower toxicity compared with other transition metal complexes. According to published reports, iron-mediated ATRP has been applied in ATRP. Sawamoto et al. [35] reported Fe-catalyzed ATRP of MMA using a FeCl2(PPh3)2 complex as the catalyst at 80  C in toluene. During a similar process, Matyjaszeaski and coworkers [36] reported the Fe-mediated ATRP of styrene (St) and MMA using FeBr2 as catalyst in the presence of various types of liagnd system. Zhu’s group [37] firstly reported Femediated ICAR ATRP of MMA with FeCl3 6H2O/triphenylphosphine (PPh3) as a complex catalyst, azobis(isobutyronitrile) as a thermal radical initiator and 1,4-(2-bromo-2-methylpropionate)benzene as an ATRP initiator. In some other studies, Noh’s group reported some works on Fe-mediated ATRP using pyridyphosphine as the ligand [38,39]. To the authors’ knowledge, there is no report on Femediated ICAR ATRP performed in ionic liquid based microemulsion. In this study, the synthesis of poly(methyl methacrylate) (PMMA) with narrow MWD was investigated via ICAR ATRP in ionic liquid based microemulsion. The polymerization was carried out by using CCl4 as initiator, FeCl3 6H2O/hexamethylene tetramine as catalyst complex, and 2,20 -azobis(isobutyronitrile) (AIBN) as reducing agent. The chain end functionality of the obtained PMMA was characterized by proton nuclear magnetic resonance (1H NMR) and demonstrated by chain extension experiment.

in a 100-mL three-neck round-bottom flask equipped with magnetic stirring bar under a pure nitrogen atmosphere. The mixture was stirred to form transparent microemulsion, and then predetermined amount of FeCl3 6H2O, HMTA, AIBN and CCl4 were added. The system was then stirred until microemulsion obtained. The flask was placed in an oil bath held by a thermostat at the desired reaction temperature to polymerize under stirring. After the desired polymerization time, the flask was cooled by immersing into ice water. The reactant was pored into a large amount of methanol for precipitation. The obtained PMMA was washed with a large amount of water, and then vacuum-dried at 60  C for one day until constant weight. Monomer conversion was determined by gravimetry. A typical example of the general procedure is as follows: 11.3672 g [bmim][PF6] (40 mmol) and 1.8222 g CTAB (5 mmol) was mixed, then 0.6074 g MMA (6.1 mmol), 0.0002 g FeCl3 6H2O (0.0006 mmol), 0.0002 g HMTA (0.0012 mmol), 0.0019 g CCl4 (0.012 mmol) and 0.0002 g AIBN (0.0012 mmol) were in turn added to the flask. 2.3. Measurements The number-average molecular weights (Mn,GPC) and MWDs of the obtained PMMA were determined by gel permeation chromatography (GPC) with a Waters 1515 equipped with refractive index detector using tetrahydrofuran (THF) as a mobile phase at a flow rate of 1.0 mL/min. Polystyrene standards were used to calibrate the columns. The universal calibration can be used to correct the molecular weights obtained for polystyrene to PMMA using MarkHouwink-Sakarada equation (NHS) between Polystyrene and PMMA with NHS parameters: KPSt ¼ 15.8  105 dL/g and aPSt ¼ 0.704; KPMMA ¼ 12.2  105 dL/g and aPMMA ¼ 0.69 [41]. Theoretical molecular weights (Mn,th) of the resulting MMA was calculated by the following equation:


MnðthÞ ¼ ½MMA0 =½I0  WMMA  x

(1)

2. Experimental

where, [MMA]0 is the initial concentration of MMA, [I]0 is the initial concentration of CCl4 and WMMA is Mn,GPC of MMA, x is the monomer conversion. 1 H NMR spectrum was recorded on a Bruker 400 MHz Spectrometer using CDCl3 as the solvent at ambient temperature and tetramethylsilane as the internal standard. The average size was measured by the dynamic light scattering with a detector to measure the intensity at a light scattering angle of 173 at room temperature. Samples were diluted before measuring with THF.

2.1. Materials

3. Results and discussion

The ionic liquid [bmim][PF6] was prepared according to a literature procedure [40]. MMA was purchased from Tianjin Fuchen Chemical Reagents Factory, China. It was distilled under reduced pressure prior to use. Carbon tetrachloride (CCl4, 99%), obtained from Hunan HuiHong Reagent Co., Ltd., was used without further purification. AIBN, obtained from Shanghai 4th factory of chemicals, China, was recrystallized twice from methanol. Ferric chloride hexahydrate was purchased from Shanghai Qingfeng Chemical Factory, China. HMTA and hexadecyl trimethyl ammonium bromide (CTAB) were obtained from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Other regents were used as received.

3.1. Preparation of MMA by ICAR ATRP in ionic liquid based microemulsion

2.2. Polymerization The ionic liquid based microemulsion was prepared by dropwise addition of MMA into the CTAB/[bmim][PF6] at room temperature

PMMA homopolymer was prepared by ICAR ATRP process in ionic liquid based microemulsion using FeCl3$6H2O/HMTA/AIBN catalyst system as described in Scheme 2. 3.2. Kinetics of polymerization of MMA by ICAR ATRP in ionic liquid based microemulsion ICAR ATRPs of MMA were carried out at 60  C in ionic liquid based microemulsion with the molar ratio of [MMA]0/[CCl4]0/[FeCl3 6H2O]0/[HMTA]0/[AIBN] at 500:1:0.05:0.1:0.1. The kinetics experimental results are presented in Fig. 1. The straight line of ln([M]0/ [M]) versus time is indicative of first-order kinetics and the number of the active species is constant throughout the polymerization

G. Wang et al. / Polymer 53 (2012) 1093e1097

in ionic liquid based microemulsion COOCH3

C

Scheme 2. Mechanism of ICAR ATRP of MMA in ionic liquid based microemulsion.

process. An induction period (about 50 min) was observed. The existence of the induction period indicated that it took some time to establish the dynamic equilibrium between the concentration of Fe(II) and Fe(III) species as the reaction proceeded. The apparent rate constant (kapp p ) for the reaction determined according to the slope of Fig. 1 was 8.47  105 s1. Fig. 2 illustrates the molecular weight and MWD dependence on monomer conversion for ICAR ATRP of MMA in ionic liquid at 60  C with CCl4/FeCl3 6H2O/HMTA as initiator system. As can be seen, there is a good linear relationship between the Mn,GPC and conversion when the conversion is beyond 20% and the Mn,GPC values are in good agreement with the Mn,th, indicating that the polymerization reaction proceeded in a living manner in this case. The MWD of the obtained PMMA had large values at the beginning of polymerization and slowed down with the progress of ICAR ATRP in ionic liquid based microemulsion. It indicated that radical terminations occurred at the early stage of polymerization. On the basis of the above discussion, it can be inferred that the Femediated ICAR ATRP of MMA proceeded in a well-controlled manner. 3.3. Effect of amount of catalyst on polymerization Since living polymerizations are mediated by transition metal complexes, the catalyst plays a crucial role in the control of polymerization. Fe-mediated ICAR ATRP was carried out in ionic liquid based microemulsion with the molar ratio of [MMA]0/[CCl4]0/ [HMTA]0/[AIBN] at 500:1:0.1:0.1 under varied amounts of FeCl3$6H2O. The effect of the amount of catalyst on the polymerization was investigated. As shown in Fig. 3, linear first-order kinetics was observed, indicating that the concentration of propagation radicals was constant throughout the polymerization process in all reactions. The induction period was significantly reduced at the molar ratio of [CCl4]/[FeCl3$6H2O] ¼ 1:0.1. The polymerization rate increased with increasing the amount of FeCl3$6H2O and the apparent rate constants were 9.72  105 s1, 8.47  105 s1, 6.67  105 s1, respectively.

80

Conversion (%) ln( [M]0/[M])

Conversion (%)

70 60

2.2

1.6

1.4

1.4

7

Time (h) Fig. 1. Kinetic plot of conversion and ln([M]0/[M]) of iron-mediated ICAR ATRP of MMA versus time at 60  C in ionic liquid based microemulsion.

1.22

80

3+

[ CCl4] /[ Fe

] =1:0.02

3+ [ CCl4] /[ Fe ] =1:0.05 3+ [ CCl4] /[ Fe ] =1:0.1

1.2 1.0 0.8 0.6

0.0

6

60

In a typical ICAR ATRP system, a low amount of lower-oxidationstate metal complex is generated by decomposition of a thermal initiator through the reduction of higher-oxidation-state metal. So the amount of AIBN has a vital role in ICAR ATRP. A series of experiments were carried out to investigate the effect of amount of AIBN on polymerization with the ratio of [MMA]0/[CCl4]0/[FeCl3 6H2O]0/[HMTA]0 at 500:1:0.05:0.1.

0.0

5

40

3.4. Effect of the amount of AIBN on polymerization

0.2

4

20

Fig. 4 illustrates that the Mn,GPC increased with conversion in all cases and were in good agreement with the Mn,th, and the MWD remained relatively low when the conversion was beyond 20%. There were no significant difference between the Mn,GPC with three varied concentrations of FeCl3 6H2O. The MWD values were higher with the ratio of [CCl4]/[FeCl3 6H2O] ¼ 1:0.02 than that with the ratio of [CCl4]/[FeCl3 6H2O] ¼ 1:0.1. However, it was noticed that the polymerization was controlled even if the molar ratio of [CCl4]/ [FeCl3 6H2O] ¼ 1:0.02, indicated that the polymerization proceeded via a controlled/‘living’ polymerization. However, at lower conversion the MWD was broad, which was attributed to variation in the number of activation/deactivation cycles that polymer radicals underwent.

0.2 3

0

Fig. 2. Dependence of Mn,th and MWD versus conversion at 60  C in ionic liquid based microemulsion. The experimental conditions are the same as described in Fig. 1.

10 2

1.26

Conversion (%)

0.4

1

1.30

1.24 0

0.4

0

1.32 1.28

20

0

1.34

10000

1.6

0.6

1.36

20000

1.8

0.8

30

1.38

30000

1.8

1.0 40

1.40

40000

2.0

1.2

50

1.42

WMD

2.0

ln( [M]0/[M])

90

50000

n

COOCH3

1.44 Mn,th Mn,GPC

WMD

CH2

-1 Mn ( g·mol )

C

CH2

60000

CH3

CCl4,FeCl3 H2O,HMTA with AIBN as reducing agent

ln( [M]0/[M])

CH3

1095

0

1

2

3

4

5

6

7

Time (h) Fig. 3. Effect of the varied amount of FeCl3$6H2O on Fe-mediated ICAR ATRP of MMA in ionic liquid based microemulsion.

G. Wang et al. / Polymer 53 (2012) 1093e1097

95000 90000 85000 80000 75000 70000 65000 60000 55000 50000 45000 40000 35000 30000 25000 20000 15000 10000 5000 0

Table 3 Effect of the concentration of surfactant on polymerization at 60  C.

2.0 Mn,th 3+ Mn,GPC [ CCl4] /[ Fe ] =1:0.02 3+ Mn,GPC [ CCl4] /[ Fe ] =1:0.05 3+ Mn,GPC [ CCl4] /[ Fe ] =1:0.1 3+ WMD [ CCl4] /[ Fe ] =1:0.02 3+ WMD [ CCl4] /[ Fe ] =1:0.05

1.9

Run

Ra (w/w)

Time (h)

Conversion (%)

Mn,th (g mol1)

Mn,GPC (g mol1)

MWD

Db (nm)

1 2 3 4

2 3 4 6

8.5 5.5 4.3 3.8

48.22 76.14 77.82 79.37

24,100 38,100 38,900 39,700

29,500 49,900 50,400 50,100

1.24 1.25 1.26 1.41

14 10 9 7

1.8 1.7 1.6

3+ WMD [ CCl4] /[ Fe ] =1:0.1

1.5

WMD

-1 Mn ( g mol )

1096

a b

R ¼ wCTAB/wMMA. D ¼ diameter.

1.4 1.3 0

10

20

30

40

50

60

70

80

1.2 90

Conversion (%) Fig. 4. Evolution of Mn,th and MWD versus conversion at 60  C in ionic liquid based microemulsion under varied amount of FeCl3 6H2O. The experimental conditions are the same as described in Fig. 3.

It can seen from Table 1 that, the polymerization rate increased with increasing the amount of AIBN, resulted in the increasing amount of Fe(II) complexes generated from Fe(III) complexes. The Mn,GPC values were consistent with the theoretical ones with low MWD, indicating that the polymerization was controlled. However, the MWD values were broad when the ratio of [CCl4]0/[AIBN]0 was 1:0.5, due to the occurrence of radical termination. 3.5. Effect of temperature on polymerization The effect of temperature on the polymerization was investigated under different temperatures. As shown in Table 2, the polymerization rate increased with increasing temperature at all temperatures. The Mn,GPC values were close to the theoretical values. However, the MWD value was higher at 80  C than that at other temperatures. This may be due to the faster decomposition of AIBN at 80  C. 3.6. Effect of the concentration of surfactant on polymerization In ionic liquid based microemulsion polymerization, the concentration of surfactant has an important influence on the stability and the final polymer particle size. In the current study,

four different concentrations of surfactant were employed to investigate the influence of the concentration of surfactant on the Fe-mediated ICAR ATRP process. As shown in Table 3, the polymerization rate increased with increasing the concentration of surfactant. The Mn,GPC values were close to the corresponding theoretical values and the MWD values increased with increasing the amount of surfactant. However, the polymerization was uncontrolled when the ratio of wCTAB/wMMA was 6, because of faster polymerization rate. The particle size decreased with increasing the concentration of surfactant and the diameter of particle was less than 14 nm and the system kept transparent, indicating that the polymerization proceeded as microemulsion. 3.7. Analysis of chain end of PMMA and chain extension of PMMA The PMMA prepared by Fe-mediated ICAR ATRP at 60  C was analyzed by 1H NMR spectrum, as shown in Fig. 5. The chemical shift at 3.79 ppm (a in Fig. 5) corresponded to the methyloxy group next to the halogen chain end, which deviated from the chemical shift 3.60 ppm (d in Fig. 5) because of the electron attracting function of u-Cl atom, as reported by Sawamoto [35]. The chemical shifts at 0.77e1.22 ppm (b in Fig. 5) and 1.39e2.13 ppm (c in Fig. 5) were attributed to the protons of methyl groups and methylene group, respectively. The obtained PMMA (Mn,GPC ¼ 15,000 g/mol, MWD ¼ 1.30) was used as macroinitiator to perform chain extension experiment. There was a large shift in the molar molecular weights, indicating that the chain extended PMMA (Mn,GPC ¼ 31,800 g/mol, MWD ¼ 1.34) was obtained (Fig. 6). It demonstrated that the chain experiment was successful and indicated the ‘living’ features of the chain end.

d

Run

Ratio of [CCl4]0/[AIBN]0

Time (h)

Conversion (%)

Mn,th (g mol1)

Mn,GPC (g mol1)

MWD

1 2 3 4

1:0.05 1:0.1 1:0.2 1:0.5

5.6 4.5 3.2 2.3

60.35 66.18 67.82 70.26

30,200 33,100 33,900 35,100

41,700 44,600 43,700 44,200

1.28 1.25 1.27 1.41

b

b CH3 c CH3 CH2-C nCH2-C Cl O=C O=C O O CH3 CH3 a d

Table 1 Effect of the amount of AIBN on polymerization at 60  C.

Table 2 Effect of temperature on polymerization.

c

a

Run

Temperature ( C)

Time (h)

Conversion (%)

Mn,th (g mol1)

Mn,GPC (g mol1)

MWD

1 2 3 4

50 60 70 80

8.2 5 3.6 2.2

55.71 71.06 75.24 78.73

27,900 35,500 37,600 39,400

39,600 47,700 49,200 49,900

1.29 1.25 1.26 1.37

8

7

6

5

4

3

2

1

0

Chemical shift (ppm) 1

Fig. 5. H NMR spectrum of PMMA (Mn,GPC ¼ 11,900 g/mol, MWD ¼ 1.30).

G. Wang et al. / Polymer 53 (2012) 1093e1097

1097

initiator showed that the chain ends of the obtained PMMA-Cl have high functionality. Macroinitiator PMMA Mn,GPC=15000 g/mol WMD=1.30

Chain extended PMMA Mn,GPC=31800 g/mol WMD=1.34

10

11

12

13

14

15

16

17

18

19

Elution time (min) Fig. 6. GPC traces of (a) the macroinitiator PMMA-Cl and (b) the chain extended PMMA.

4. Conclusion In this investigation, ICAR ATRP of MMA was successfully performed at 60  C in ionic liquid based microemulsion with CCl4 as initiator, FeCl3 6H2O/HMTA as catalyst complex and AIBN as reducing agent. CTAB was used as surfactant in this study. Welldefined PMMA with narrow MWD was obtained with this system. The kinetics results indicated that the polymerization is a living/controlled polymerization process, as demonstrated by the first-order kinetics and a linear increase of the molecular weights with monomer conversion, as well as relatively narrow molecular weight distribution. The polymerization rate increased when the molar ratio of [CCl4]/[FeCl3 6H2O] increased from 1:0.02 to 1:0.1. Furthermore, the polymerization proceeded in a controlled/‘living’ process even though the molar ratio of [CCl4]/[FeCl3 6H2O] was 1:0.02. It demonstrated that the catalyst system was highly efficient used for the ICAR ATRP of MMA in ionic liquid based microemulsion. Increasing the concentration of AIBN, the polymerization rate increased. However, the polymerization proceeded in an uncontrolled fashion when the molar ratio of [CCl4]/[AIBN] was 1:0.5. The polymerization increased with the reaction temperature. The MWD became broader at 80  C. The concentration of CTAB had a profound effect on the polymerization and particle size. The polymerization rate increased and the particle size decreased from 14 nm to 7 nm with increasing the ratio of wCTAB/wMMA from 2 to 6. However, the polymerizations were poorly controlled when the ratio of wCTAB/wMMA was 6. The chain extension of PMMA macro-

References [1] Wang JS, Matyjaszewski K. Macromolecules 1995;28:7572. [2] Kato M, Kamigaito M, Sawamoto M, Higashimura T. Macromolecules 1995;28: 1721. [3] Plichta A, Li WW, Matyjaszewski K. Macromolecules 2009;42:2330. [4] Matyjaszewski K, Jakubowski W, Min K, Tang W, Huang JY, Braunecker WA, et al. Proc Natl Acad Sci USA 2006;103:15309. [5] Mueller L, Matyjaszewski K. Macromol React Eng 2010;4:180. [6] Dong HC, Matyjaszewski K. Macromolecules 2008;41:6868. [7] Min K, Gao HF, Matyjaszewski K. Macromolecules 2007;40:1789. [8] Kwak Y, Magenau AJD, Matyjaszewski K. Macromolecules 2011;44:811. [9] Braunecker WA, Matyjaszewski K. Prog Polym Sci 2007;32:93. [10] Cheng CJ, Gong SS, Fu QL, Shen L, Liu ZB, Qiao YL, et al. Polym Bull 2011;66: 735. [11] Li WW, Matyjaszewski K. Macromolecules 2011;44:5578. [12] Eslami H, Zhu SP. Polymer 2005;46:5484. [13] Li WW, Matyjaszewski K, Albrecht K, Moöller M. Macromolecules 2009;42: 8228. [14] Stoffelbach F, Griffete N, Bui C, Charleux B. Chem Commun 2008;39:4807. [15] Li WW, Min K, Matyjaszewski K, Stoffelbach F, Charleux B. Macromolecules 2008;41:6387. [16] Kagawa Y, Zetterlund PB, Minami H, Okubo M. Macromol Theory Simul 2006; 15:608. [17] Min K, Gao HF, Matyjaszewski K. J Am Chem Soc 2006;128:10521. [18] Kagawa Y, Kawasaki M, Zetterlund PB, Minami H, Okubo M. Macromol Rapid Commun 2007;28:2354. [19] Min K, Matyjaszewski K. Macromolecules 2005;38:8131. [20] Danielsson I, Lindman B. Colloid Surf 1981;3:391. [21] Guerrero-Sanchez C, Schubert US. Polym Prep 2004;45:321. [22] Kubisa P. Prog Polym Sci 2004;29:3. [23] Li NJ, Lu JM, Xu QF, Xia XW, Wang LH. J Appl Polym Sci 2007;103:3915. [24] Qi MY, Wu GZ, Sha ML, Liu YS. Radiat Phys Chem 2008;77:1248. [25] Biedron T, Kubisa P. Macromol Rapid Commun 2001;22:1237. [26] Biedron T, Kubisa P. J Polym Sci Part A Polym Chem 2002;40:2799. [27] Chen ZZ, Yan F, Qiu LH, Lu JM, Zhou YX, Chen JX, et al. Langmuir 2010;26: 3803. [28] Lu JJ, Ding YS, Yu Y, Wu SY, Feng WG. Macromol Symp 2010;298:167. [29] Yan F, Texter J. Chem Commun 2006;25:2696. [30] Zhang GP, Zhou HH, Hu JQ, Liu M, Kuang YF. Green Chem 2009;11:1428. [31] Moniruzzaman M, Kamiya N, Nakashimaa K, Goto M. Green Chem 2008;10: 497. [32] Drury A, Chaure S, Kröll M, Nicolosi V, Chaure N, Blau WJ. Chem Mater 2007; 19:4252. [33] Yu SM, Yan F, Zhang XW, You JB, Wu PY, Lu JM, et al. Macromolecules 2008; 41:3389. [34] Zhou YX, Qiu LH, Deng ZJ, Texter J, Yan F. Macromolecules 2011;44:7948. [35] Ando T, Kamigaito M, Sawamoto M. Macromolecules 1997;30:4507. [36] Matyjaszewski K, Wei M, Xia J, McDermott NE. Macromolecules 1997;30: 8161. [37] Zhu GH, Zhang LF, Zhang ZB, Zhu J, Tu YF, Cheng ZP, et al. Macromolecules 2011;44:3233. [38] Xue ZG, He D, Noh SK, Lyoo WS. Macromolecules 2009;42:2949. [39] He D, Xue ZG, Khan MY, Noh SK, Lyoo WS. J Polym Sci Part A Polym Chem 2010;48:144. [40] Huddleston JG, Rogers RD. Chem Commun; 1998:1765. [41] Mori S, Barth HG. Size exclusion chromatography. Berlin: SpringereVerlag, ISBN 3-540-65635-9; 1999. P201.