metal composites via reversible addition-fragmentation chain transfer (RAFT) polymerization

Reactive & Functional Polymers 69 (2009) 55–61

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Reactive & Functional Polymers journal homepage: www.elsevier.com/locate/react

Preparation and characterization of poly(styrene)/metal composites via reversible addition-fragmentation chain transfer (RAFT) polymerization Di Zhou a,b, Xiulin Zhu a,*, Jian Zhu a, Zhenping Cheng a a b

Key Lab. of Organic Synthesis of Jiangsu Province, School of Chemistry and Chemical Engineering of Soochow (Suzhou) University, Suzhou 215006, China Jiangsu Key Lab. of Advanced Functional Materials, Chemistry Department, Changshu Institute of Technology, Changshu, China

a r t i c l e

i n f o

Article history: Received 28 April 2008 Received in revised form 15 October 2008 Accepted 16 October 2008 Available online 25 October 2008 Keywords: RAFT polymerization Dithiocarbamate Poly(styrene)

a b s t r a c t The expectant dithiocarbamate group end-functional poly(styrene) (PS) with a controlled molecular weight and low molecular weight distribution was synthesized conveniently via reversible addition-fragmentation chain transfer (RAFT) polymerization and was used to prepare polymer/metal composites with coordination chemistry. By the self-assembly technique, PS coordinated with the rare earth metal in N,Ndimethylformamide (DMF) to generate the fluorescent Eu–PS and Sm–PS complexes. Furthermore, PScoated spherical silver nanoparticles (AgNPs) were prepared by reducing Ag+ to Ag0 under ultrasound irradiation in the presence of DMF and H2O. The well core/shell structure of the AgNPs was characterized by transmission electron microscopy (TEM). Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction Polymer/metal composites offer tremendous possibilities for combining properties stemming from both the organic components of a polymer and the inorganic components of metal [1–4]. Due to the properties of the self-assembly technology, such as simplicity and the high level of order on a molecular scale, it has been widely used to prepare polymer/metal composites [5,6]. On the other hand, silver nanoparticles (AgNPs) as a special material have been the subject of intense interest due to its importance in chemistry [7], biology [8], optics [9], electronics [10], magnetics [11], and pharmacy [12]. Various other approaches have been developed to prepare the AgNPs with a narrow size distribution [13–16]. One could control this parameter during chemical synthesis by using a larger amount of the stabilizer, such as surfactants [17] or polymers [18], to avoid aggregation of the nanoparticles. Polymeric materials with different structures are usually used as stabilizers to prevent nanoparticle agglomeration and precipitation [19–23]. For example, poly(vinylpyrrolidone) (PVP) has been widely applied as an effective stabilizer for AgNPs [24,25]. The reversible additionfragmentation chain transfer (RAFT) polymerization is one convenient way to prepare functional polymers, especially expectant end-labeled polymers with designed structures (controlled molecular weight and low molecular weight distribution), by designing proper Z and R groups of RAFT agents (Scheme 1) [26–32]. Zhou et al. reported the synthesis of ruthenium(II)-centered polymers * Corresponding author. Fax: +86 512 65112796. E-mail address: [email protected] (X. Zhu). 1381-5148/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2008.10.010

via the RAFT polymerization with a designed R group of the RAFT agent [33,34]. Nuopponen et al. synthesized copolymer PMAA-bPNIPAM using the RAFT technique and prepared gold nanoparticles protected with PMAA-b-PNIPAM [35]. Several authors have reported that a hydrosulfide group (–SH) end-labeled polymer was conveniently obtained by reducing the end-group of the RAFT resulting polymer and, thus, that polymer-stabilized gold nanoparticles could be formed via SH bound to an Au atom [36–44]. Dithiocarbamate derivatives were used as the capping ligands to stabilize the silver or gold nanoparticles [45,46]. This work focused on the convenient synthesis of the dithiocarbamate group end-functional poly(styrene) (PS) via the RAFT polymerization using a designed proper Z group of the RAFT agent. Subsequently, the end-functional PS was directly applied both in the fabrication of polymer/metal composites with the fluorescent rare earth metal as the line macroligand (Scheme 2) and in the preparation of polymer-coated silver nanoparticles as the polymeric stabilizer (Scheme 3). 2. Experimental 2.1. Materials All materials were purchased from Shanghai Chemical Reagents Co., Ltd., China and J&K-Acros Co., Ltd., Styrene (St., analytical grade) was washed with an aqueous solution of sodium hydroxide (5 wt%) three times and then with deionized water until neutralization. After drying with anhydrous magnesium sulfate, the styrene was distilled under reduced pressure and kept in a refrigerator at 2 °C. The synthesis methods for the dithiocarba-

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S

R

X

S

R

+ n

X Y n

Y

Z

S

S

Radicals ource

Z

Scheme 1. Overall reaction in RAFT polymerization.

n

+ M =dithiocarbamate group

self-assembly DMF, r.t.

M

n

M=low molecular weight Eu or Sm complexes

n=1,2

Scheme 2. Synthesis of polymer/metal composites by self-assembly.

eral times to remove any unreacted low molecular metal complexes and was dried at room temperature under vacuum. 2.4. Preparation of polymer-coated silver nanoparticles Silver nanoparticles were prepared by reducing AgNO3 under ultrasound irradiation in the presence of the obtained PS. In a typical synthesis, 1 mL of AgNO3 solution (1.0  10 3 mol/L in H2O) was added dropwise to a 100 mL PS solution (1.0  10 4 mol/L in DMF). The mixture solution was exposed to high-intensity ultrasound irradiation under ambient conditions for 0.5 h at room temperature. Ultrasound irradiation was accomplished using a KQ-500 sonication bath with a 500 W output power. 2.5. Characterization

ultrasound irradiation + AgNO3 DMF, H2O = dithiocarbamate group

Scheme 3. Preparation of polymer-coated AgNPs under ultrasound irradiation.

mates (BTC and BIC, Scheme 4) were reported in our previous papers [47,48]. The low molecular Eu complex (Eu(DBM)2Cl) and Sm complex (Sm(DBM)2Cl) were synthesized by the classical process and characterized by elemental analyses [49]. Other materials were used without further purification.

The molecular weight (Mn) and molecular weight distribution (Mw/Mn) of the PS were determined with a waters 1515 gel permeation chromatographer (GPC) equipped with refractive index detector, using the HR 1, HR 3, and HR 4 columns. The calibration was performed with the PS (molecular weight range 100–500,000) as standard samples. Tetrahydrofuran (THF) was used as the eluent at a flow rate of 1.0 mL min 1 operated at 30 °C. 1H NMR spectra of the polymers were recorded on an INOVA400 nuclear magnetic

A

2.2. The RAFT polymerizations of styrene The following procedure was typical. A solution of styrene (5.2075 g, 50 mmol) and BTC (0.0235 g, 0.1 mmol) was prepared in a 10 mL ampule. The content was purged with argon for approximately 10 min to eliminate any oxygen. The ampule was then flame-sealed. The polymerization reaction was performed at the appropriate temperature. After the desired reaction time, the ampule was quenched in ice water and then opened. The reaction mixture was diluted with a small amount of tetrahydrofuran (THF) (2 mL) and precipitated in large amount of methanol (300 mL). The polymer was obtained by filtrating and was dried at room temperature under vacuum oven to constant weight. The conversion was determined gravimetrically.

(c) (b) (a) 15

16

17

18

19

20

21

22

23

24

Time (min)

B

2.3. Synthesis of polymer/metal composites by self-assembly The obtained PS (1.0  10 5 mol) and 10 mL DMF were added to a 50 mL flask. The mixture was heated slightly to form a homogeneous solution. Then, 0.5  10 5 mol low molecular metal complex EuCl(DBM)2 or SmCl(DBM)2 was added. The mixture was stirred at room temperature overnight. The complex was obtained by precipitation into a large amount of methanol, followed with filtration. After these processes, the product was washed with methanol sev-

(c) (b) (a)

S

S S

S

14 N

N N BT C

16

17

18

19

20

21

22

23

24

Time (min)

N N

15

BIC Scheme 4. Chemical structures of RAFT agents.

Fig. 1. (A) GPC plots of the resulting PS by BTC ((a) Mn = 21,300, Mw/Mn = 1.11), Eu– PS (b), and Sm–PS (c); (B) GPC plots of resulting PS by BIC ((a) Mn = 33,800, Mw/ Mn = 1.10), Eu–PS ((b) Mn = 63,900, Mw/Mn = 1.43) and Sm–PS ((c) Mn = 66,600, Mw/ Mn = 1.41).

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the end-functional PS for further use. The results of the polymerizations were reported in detail in our previous paper [47,48].

A 35000 389

30000

3.2. Synthesis of fluorescent polymer/metal composites by selfassembly

Intensity (counts)

(b)

25000 397 391

332

20000

(a)

15000 10000

(c) 276

5000

254

0 250

300

350

400

450

500

550

600

Wavelength (nm)

B 40000

388

S

(a)

30000

O

306 419

n

S

N

25000 20000

Ph

(b)

35000

Intensity (counts)

The obtained PS with the dithiocarbamate moiety at the end of the chain was complexed with the rare earth metal europium (Eu) and samarium (Sm) to obtain polymer/metal composites, which were characterized by gel permeation chromatography (GPC). The typical GPC plots shown in Fig. 1 explicitly illustrated the changes in Mn of the PS before and after self-assembly with Eu or Sm in DMF. In Fig. 2A, the GPC trace of the polymer/metal composites showed two peaks. One of these peaks was in the same position with original BTC resulting PS, and the other new peak was detected with about twice the molecular weight of the original PS, which indicated that two different structures of the polymer/ metal composites (Scheme 5, 1 and 2) were formed. The reason

N

N

O

244

Ph

15000 10000

1

M

2

2

Cl

252 282

Ph

5000

(c) 390

255

S

O

N

0 250

300

350

400

450

500

550

M

600 n

Wavelength (nm)

S

N

Ph

Fig. 2. (A) Excitation spectra of Eu complexes: (a) Eu(DBM)2Cl; (b) Eu–PS complex obtained using BTC as RAFT agent; and (c) Eu–PS complex obtained using BIC as RAFT agent. (B) Excitation spectra of Sm complexes: (a) Sm(DBM)2Cl; (b) Sm–PS complex obtained using BTC as RAFT agent; and (c) Sm–PS complex obtained using BIC as RAFT agent.

3. Results and discussion

Ph

Ph

O n

S

N

N

3

M O Ph 2

2

Cl

Scheme 5. Possible structure of polymer/metal composites, M = Eu or Sm.

Table 1 Metal ion concentrations measure by ICP-AESa. Polymer

Metal ion

Nb

PS by BTC (Mn = 21,300, Mw/Mn = 1.11)

Eu(DBM)2Cl Sm(DBM)2Cl

0.63 0.69

PS by BIC (Mn = 33,800, Mw/Mn = 1.10)

Eu(DBM)2Cl Sm(DBM)2Cl

0.47 0.48

3.1. Synthesis of end-functional PS via RAFT polymerization The RAFT polymerization technique is an efficient way to prepare end-functional polymers with predesigned structure. In this work, the ‘‘living”/controlled polymerizations of styrene in bulk using BTC and BIC as RAFT agents were carried out to synthesize

2

Cl S

resonance (NMR) instrument using CDCl3 as a solvent and tetramethylsilane (TMS) as the internal standard. The emission and steady-state fluorescence spectra were recorded on a FLS920, Edinburgh Instruments. The source of light was a CW 450 W xenon arc lamp. The fluorescence was measured in solid powder packed between silex glass films at room temperature, and the silt widths of the monochromators were both 1 nm. The Ag nanoparticles were characterized using transmission electron microscopy (TEM, TecnaiG220, FEI, America). The metal ion concentrations were determined by VISTA-MPX CCD Simultaneous ICP-AES, and the operating conditions are as follows: plasma flow rate, 15 L min 1; carrier gas (Ar) flow rate, 1.5 L min 1; incident power (kW), 1.2 kW; and vaporization press, 240 KPa.

2 O

N

a

Measured using low molecular weight metal complexes as standard samples. N is the mole ratio between metal ion and PS chain (or average metal atom number per PS chain). b

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for this may be that the triazole group at the end of PS could form both intramolecular and intermolecular coordination polymers [50–52]. In the case of the obtained PS by BIC (Fig. 2B), the GPC trace of the polymer/metal composites showed only one peak with twice the molecular weight of the original PS, which indicated that most of the polymer chains carried out the self-assembly reaction with Eu or Sm and formed the new metal-centered linear polymer 3, as shown in Scheme 5. Molecular weight determination by GPC confirmed that these PS macroligands were chelated to rare earth metal precursor complexes. Furthermore, ICP-AES was also used for the determination of metal ions attached to the end of the polymer. The amounts of metal ions coordinated with the polymer were analyzed by ICP-AES, as shown in Table 1. The samples were purified by three cycles of dissolving in DMF and precipitating into the methanol, followed by washing with absolute ethyl alcohol. The results listed in Table 1 show that there were on average about 0.66 metal atoms per BTC resulting PS chain, which also suggested

A

that the triazole formed two types of coordination polymers with the metal ion; additionally, there were about 0.50 metal atoms per BIC resulting PS chain, which verified that the metal-centered linear polymer was formed. Thus, polymer/metal composites were constructed by combining the RAFT polymerization technique with coordination chemistry. Rare earth metal-based materials are of special interest in optical excitation and emission because of their high luminescent quantum efficiencies. Here, fluorescence spectra of the obtained polymer/metal complexes and original low molecular weight metal complexes were investigated at room temperature in a solid. The excitation spectra of these were quite different, as shown in Fig. 2. There were two strong absorptions in both the Eu(DBM)2Cl and Sm(DBM)2Cl excitation spectra. In the case of the polymer/metal composites, they showed a broadband ranging absorption only, and the excitation wavelength was about 389 nm. The reason for this is that the details of the rare earth metal excitation and

18000

612 16000

(b)

Intensity (counts)

14000 12000 10000 8000

647

6000

(c)

4000 2000

563

700

600

(a)

0 450

500

550

600

650

700

750

Wavelength (nm)

B

6000

645

5000

612 Intensity (counts)

4000

(b)

(c)

3000

2000

1000

599

(a) 701

0 450

500

550

600

650

700

750

Wavelength (nm) Fig. 3. (A) Fluorescence spectra of the resulting PS by BTC and its metal complexes in a solid: (a) PS, Mn = 21,300, Mw/Mn = 1.11; (b) Eu–PS complex; (c) Sm–PS complex. (B) Fluorescence spectra of resulting PS by BIC and its metal complexes in solid: (a) PS, Mn = 33,800, Mw/Mn = 1.10; (b) Eu–PS complex; and (c) Sm–PS complex.

D. Zhou et al. / Reactive & Functional Polymers 69 (2009) 55–61

59

Fig. 4. TEM micrographs of AgNPs with the resulting PS by BTC (Mn = 11,300, Mw/Mn = 1.10) as capping reagent under different ultrasound irradiation times.

Fig. 5. TEM micrographs after ultrasound irradiation for 0.5 h. (a, b) 1 mL 1.0  10 3 mol/L AgNO3 added to 100 mL 1.0  10 4 mol/L (DMF solvent) resulting PS by BTC (Mn = 22,300, Mw/Mn = 1.10). (c, d) 1 mL 1.0  10 3 mol/L AgNO3 dropped to 100 mL 1.0  10 4 mol/L (DMF solvent) resulting PS by BIC (Mn = 33,800, Mw/Mn = 1.10).

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emission spectra are particularly sensitive to structural details of the coordination environment [53–58]. These results also indicated that the structures of the Eu and Sm complexes were changed and that they bonded with dithiocarbamate units. As can be seen from the fluorescence spectra of these polymer/metal composites (Fig. 3), the emission spectra of the Eu–PS complexes recorded from 450 to 750 nm, with excitation at 389 nm, showed three major emission bands at 590, 612 and 700 nm, corresponding to the 5D0 ? 7FJ (J = 1, 2, 4) transitions. Among these transitions, 5 D0 ? 7F2 was the strongest. The emission spectra of the Sm–PS complexes are also shown in Fig. 4 under excitation at 389 nm. Three emission peaks were observed centered at 563, 600 and 647 nm. These peaks could be assigned to the 4G5/2 ? 6H5/2, 4 G5/2 ? 6H7/2, 4G5/2 ? 6H9/2 transitions, respectively, where the 4 G5/2 ? 6H9/2 transition was the strongest. 3.3. Preparation of polymer-coated silver nanoparticles PS-coated silver nanoparticles were prepared by means of the adsorption of stabilizers to reduce the surface energy of the AgNPs, and the nanostructures at various stages of the growth process were characterized by TEM. Fig. 4 shows typical images of the sample taken from the reaction mixture after the solution was exposed to high-intensity ultrasound irradiation under ambient conditions for 5, 10, 20 and 30 min, respectively. Due to the quick reduction process, the AgNPs were formed immediately in the initial reaction mixture, as shown in Fig. 4. However, irregular silver nanoparticles were initially observed at 5, 10, and 20 min. After ultrasound irradiation for 30 min, the reaction was almost finished, and the main

products were uniform silver spherical nanoparticles with a well core/shell structure. In this case, the size of the particles was about 145 nm. The black middle part of the sphere was the core with a diameter of about 116 nm, and the interfacial part of the sphere was the shell made of the resulting PS by BTC with a thickness of about 14.5 nm. To show the effect of the dithiocarbamate group end-functional PS on the formation of silver nanoparticles, several different experiments were carried out. The TEM images in Fig. 5 show silver nanoparticles prepared in the presence of the resulting PS by BTC and BIC under ultrasound irradiation. As can be seen from Figs. 4 and 5, the diameter of the AgNPs became larger as the molecular weight of PS increased (Mn = 11,300, Mw/Mn = 1.10; Mn = 22,300, Mw/Mn = 1.10; and Mn = 33,800, Mw/Mn = 1.10, respectively). The reason for this may be that the PS with a high molecular weight had lower movement ability and the end-groups could not be easily released in the DMF and H2O media compared to those with low molecular weights; thus, the dithiocarbamate group had difficulty bonding with the Ag atom. Additionally, with PS bonding to the particle surface and acting as an outer block, the Ag nanoparticles could not aggregate in water; thus, the well core/shell (silver/PS) structure particles with a good size distribution could be formed and had almost no agglomeration. However, as shown in Fig. 6, in the cases without PS (e, f) and using normal thermal polymerized PS (g, h), the AgNPs seemed to be covered by PS, and there were no regular silver nanoparticles or well core/shell (silver/PS) structure particles formed. The reason for this was that PS partially covered the surface of the Ag particles because of its high surface energy, but the force of physical absorbability was lower than

Fig. 6. TEM micrographs after ultrasound irradiation for 0.5 h. (e, f) 1 mL 1.0  10 3 mol/L AgNO3 added to 100 mL DMF. (g, h) 1 mL 1.0  10 100 mL 1.0  10 4 mol/L (DMF solvent) normal thermal polymerized PS (Mn = 88,300, Mw/Mn = 2.35).

3

mol/L AgNO3 dropped to

D. Zhou et al. / Reactive & Functional Polymers 69 (2009) 55–61

HCONMe2 + 2Ag++ H2O nAg0 Agn

2Ag0

+ Me 2NCOOH + 2H+

Scheme 6. The probable mechanism of the formation of silver nanoparticles under ultrasound irradiation.

the bonding force between the dithiocarbamate group and the AgNPs. These results suggested that the dithiocarbamate group end-functional PS prepared via RAFT polymerization was an effective stabilizer for the formation of AgNPs. Ultrasound irradiation induced the formation of reducing radicals, and the probable mechanism is shown in Scheme 6. DMF and H2O were used both as solvents and as reducing agents [59,60]. 4. Conclusion The polymer/rare earth metal composites with controlled molecular weight and low molecular weight distribution were prepared via a combination of the RAFT polymerization technique with coordination chemistry. Eu–PS and Sm–PS composites exhibited strong fluorescent properties. The PS-coated spherical silver nanoparticles with a well core/shell structure were prepared by reducing Ag+ to Ag0 under ultrasound irradiation using DMF and H2O as both solvents and reducing agents. Acknowledgement The financial supports of this work by the National Nature Science Foundation of China (No. 20574050), the Science and Technology Development Planning of Jiangsu Province (Nos. BK2007702 and BK2007048), the Foundation of Changshu Institute of Technology (No. 20070702), and the Nature Science Key Basic Research of Jiangsu Province for Higher Education (No. 05KJA15008) are gratefully acknowledged. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

X.F. Wu, C.L. Fraser, Macromolecules 33 (2000) 4053. R. Shunmugam, G.N. Tew, J. Polym. Sci. A: Polym. Chem. 43 (2005) 5831. T.W. Canzler, J. Kido, Org. Electr. 7 (2006) 29. O.G. Marambio, G. del C. Pizarro, M. Jeria-Orell, M. Huerta, C. Olea-Azar, W.D. Habicher, J. Polym. Sci. A: Polym. Chem. 43 (2005) 4933. W.B. Song, M. Okamura, T. Kondo, K. Uosaki, J. Electroanal. Chem. 612 (2008) 105. L. Wang, G. Wei, C.L. Guo, L.L. Sun, Y.J. Sun, Y.H. Song, T. Yang, Z. Li, Coll. Surf. A: Physicochem. Eng. Asp. 312 (2008) 148. M.H. Rashid, T.K. Mandal, J. Phys. Chem. C 111 (2007) 16750. H.Y. Seferyan, R. Zadoyan, A.W. Wark, R.M. Corn, V.A. Apkarian, J. Phys. Chem. C 111 (2007) 18525. B.J. Wiley, Y. Chen, J.M. McLellan, Y. Xiong, Z.-Y. Li, D. Ginger, Y. Xia, NanoLetters 7 (2007) 1032. B.K. Kuila, A. Garai, A.K. Nandi, Chem. Mater. 19 (2007) 5443. P. Poddar, S. Srinath, J. Gass, B.L.V. Prasad, H. Srikanth, J. Phys. Chem. C 111 (2007) 14060. D. Guin, S.V. Manorama, J.N.L. Latha, S. Singh, J. Phys. Chem. C 111 (2007) 13393.

61

[13] R. Sardar, J.W. Park, J.S. Shumaker-Parry, Langmuir 23 (2007) 11883. [14] X. Zheng, W. Xu, C. Corredor, S. Xu, J. An, B. Zhao, J.R. Lombardi, J. Phys. Chem. C. 111 (2007) 14962. [15] Q. Shen, J. Sun, H. Wei, Y. Zhou, Y. Su, D. Wang, J. Phys. Chem. C. 111 (2007) 13673. [16] S. Tan, M. Erol, A. Attygalle, H. Du, S. Sukhishvili, Langmuir 23 (2007) 9836. [17] M. Yamamoto, Y. Kashiwagi, M. Nakamoto, Langmuir 22 (2006) 8581. [18] D. Radziuk, A. Skirtach, G. Sukhorukov, D. Shchukin, H. Möhwald, Macromol. Rapid Commun. 28 (2007) 848. [19] D.G. Yu, W.C. Lin, M.C. Yang, Bioconj. Chem. 18 (2007) 1521. [20] Y.W. Kim, D.K. Lee, K.J. Lee, B.R. Min, J.H. Kim, J. Polym. Sci. B: Polym. Phys. 45 (2007) 1283. [21] W. Lesniak, A.U. Bielinska, K. Sun, K.W. Janczak, X. Shi, J.R. Baker Jr., L.P. Balogh, NanoLetters 5 (2005) 2123. [22] O. Siiman, A. Burshteyn, J. Phys. Chem. B 104 (2000) 9795. [23] Y. Dong, Y. Ma, T.Y. Zhai, F.G. Shen, Y. Zeng, H.B. Fu, J.N. Yao, Macromol. Rapid Commun. 28 (2007) 2339. [24] W.J. Jin, H.K. Lee, E.H. Jeong, W.H. Park, J.H. Youk, Macromol. Rapid Commun. 26 (2005) 1903. [25] B. Yin, H. Ma, S. Wang, S. Chen, J. Phys. Chem. B. 107 (2003) 8898. [26] T.P.T. Le, G. Moad, E. Rizzardo, S.H. Thang, PCT Int. Pat. Appl. WO 9801478 A1 980115. [27] J. Chiefari, Y.K. Chong, F. Ercole, J. Krstina, J. Jeffery, T.P.T. Le, R.T.A. Mayadunne, G.F. Meijs, C.L. Moad, G. Moad, E. Rizzardo, S.H. Thang, Macromolecules 31 (1998) 5559. [28] S. Perrier, P. Takolpuckdee, J. Polym. Sci. A: Polym. Chem. 43 (2005) 5347. [29] L.P. Wang, Y.P. Wang, R.M. Wang, S.C. Zhang, React. Funct. Polym. 68 (2008) 643. [30] H. Mori, H. Iwaya, T. Endo, React. Funct. Polym. 67 (2007) 916. [31] A.L. Li, X.Y. Wang, H. Liang, J. Lu, React. Funct. Polym. 67 (2007) 481. [32] J. Jagur-Grodzinski, React. Funct. Polym. 49 (2001) 1. [33] G.C. Zhou, I.I. Harruna, Macromolecules 38 (2005) 4114. [34] G.C. Zhou, I.I. Harruna, Macromolecules 37 (2004) 7132. [35] M. Nuopponen, H. Tenhu, Langmuir 23 (2007) 5352. [36] C.L. McCormick, A.B. Lowe, Acc. Chem. Res. 37 (2004) 312. [37] A.B. Lowe, B.S. Sumerlin, M.S. Donovan, C.L. McCormick, J. Am. Chem. Soc. 124 (2002) 11562. [38] A. Housni, H. Cai, S. Liu, S.H. Pun, R. Narain, Langmuir 23 (2007) 5056. [39] L.W. Zhang, Y.M. Chen, Polymer 47 (2006) 5259. [40] A. Aqil, C. Detrembleur, B. Gilbert, R. Jerome, C. Jerome, Chem. Mater. 19 (2007) 2150. [41] Z. Merican, T.L. Schiller, C.J. Hawker, P.M. Fredericks, I. Blakey, Langmuir 23 (2007) 10539. [42] J.W. Hotchkiss, A.B. Lowe, S.G. Boyes, Chem. Mater. 19 (2007) 6. [43] J. Shan, M. Nuopponen, H. Jiang, E. Kauppinen, H. Tenhu, Macromolecules 36 (2003) 4526. [44] A. Aqil, H.J. Qiu, J.F. Greisch, R. Jérôme, E.D. Pauw, C. Jérôme, Polymer 49 (2008) 1145. [45] M.C. Tong, W. Chen, J. Sun, D. Ghosh, S. Chen, J. Phys. Chem. B 110 (2006) 19238. [46] Y. Zhao, W. Perez-Segarra, Q. Shi, A. Wei, J. Am. Chem. Soc. 127 (2005) 7328. [47] D. Zhou, X.L. Zhu, J. Zhu, H.S. Ying, J. Polym. Sci. A: Polym. Chem. 43 (2005) 4849. [48] H.S. Yin, X.L. Zhu, D. Zhou, J. Zhu, J. Appl. Polym. Sci. 100 (2006) 560. [49] L.R. Melby, N.J. Rose, E. Abramson, J.C. Caris, J. Am. Chem. Soc. 86 (1964) 5117. [50] X.F. Wu, J.E. Collins, J.E. McAlvin, R.W. Cutts, C.L. Fraser, Macromolecules 34 (2001) 2812. [51] K. Peter, M. Thelakkat, Macromolecules 36 (2003) 1779. [52] X.W. Xia, J.M. Lu, H. Li, S.C. Yao, L.H. Wang, Opt. Mater. 27 (2005) 1350. [53] B.S. Li, J. Zhang, S.B. Fang, Polym. Adv. Technol. 7 (1996) 108. [54] Y.F. Pan, A.N. Zheng, F.Z. Hu, H.N. Xiao, J. Appl. Polym. Sci. 100 (2006) 1506. [55] Y. Ueba, K.J. Zhu, E. Banks, Y. Okamoto, J. Polym. Sci.: Polym. Chem. Ed. 20 (1982) 1271. [56] Z. Wang, J.L. Yuan, K. Matsumoto, Luminescence 20 (2005) 347. [57] Y.P. Wang, Y. Luo, R.M. Wang, L. Yuan, J. Appl. Polym. Sci. 66 (1997) 755. [58] C.X. Du, L. Ma, Y. Xu, W.L. Li, J. Appl. Polym. Sci. 66 (1997) 1405. [59] W. Chen, J.Y. Zhang, Y. Di, Z.M. Wang, Q. Fang, W.P. Cai, Appl. Surf. Sci. 211 (2003) 280. [60] Z.L. Lei, Y.H. Fan, Mater. Lett. 60 (2006) 2256.