MADIX and “click” chemistry

European Polymer Journal 44 (2008) 1789–1795

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European Polymer Journal journal homepage: www.elsevier.com/locate/europolj

Synthesis of poly(vinyl acetate) with fluorescence via a combination of RAFT/MADIX and ‘‘click” chemistry Fen Chen, Zhenping Cheng, Jian Zhu, Wei Zhang, Xiulin Zhu * Key Laboratory of Organic Synthesis of Jiangsu Province, School of Chemistry and Chemical Engineering of Soochow (Suzhou) University, Suzhou 215006, China

a r t i c l e

i n f o

Article history: Received 8 January 2008 Received in revised form 10 March 2008 Accepted 11 March 2008 Available online 27 March 2008

Keywords: Vinyl acetate Reversible addition–fragmentation chain transfer (RAFT) ‘‘Click” chemistry Macromolecular design via interchange of xanthates (MADIX) Fluorescence

a b s t r a c t A novel x-azido-functionalized RAFT reagent, O-(2-azido-ethyl) S-benzyl dithiocarbonate (AEBDC), was synthesized and subsequently employed to mediate the reversible addition–fragmentation chain transfer (RAFT) polymerization of vinyl acetate (VAc) to prepare end-functionalized polymers. The polymerization results showed that the RAFT polymerizations of VAc could be well controlled using AEBDC as the RAFT agent. Number-average molecular weights (Mn GPC) increased linearly with monomer conversion, and molecular weight distributions were relatively narrow. 1H NMR spectrum of the poly(vinyl acetate) (PVAc) confirmed the existence of functional azido group at the end of the polymers chains. The x-azido-terminated polymers were coupled by ‘‘click” chemistry with a fluorescent alkyne, 7-propinyloxy coumarin, to prepare fluorescent PVAc. The fluorescence properties of the PVAc homopolymers before and after coupling with 7-propinyloxy coumarin in CH2Cl2 solution were investigated. Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction Poly(vinyl acetate) (PVAc) is an essential chemical material for a range of industrial and consumer products such as paints, concrete additives, adhesives, textiles, and plastics. Furthermore, Partial or totally hydrolysis of PVAc is used to prepare poly(vinyl alcohol) (PVA), which is an environmental friendly, water soluble, biocompatible polymer and extensively used in paper, paints, coatings and pharmaceutical products [1–4]. However, vinyl acetate (VAc) is a unique monomer since it can only be polymerized via a radical mechanism. Over the past few years, the preparation of well-defined PVAc has been received many attentions since the vigorous development of controlled/‘‘living” radical polymerization (CRP) techniques [3,5–17]. Until now, several papers reported the CRP of VAc via nitroxide-mediated polymerization (NMP) [5], atom transfer radical polymerization (ATRP) [6,7], and

* Corresponding author. Fax: +86 512 65112796. E-mail address: [email protected] (X. Zhu). 0014-3057/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2008.03.014

reversible addition–fragmentation chain transfer (RAFT) polymerization [8,9]. For instance, Matyjaszewski and his coworkers first utilized an initiator system of i-Bu3Al/ 2,20 -bipyridine/TEMPO (TEMPO = 2,2,6,6-tetramethyl-1piperidinyl-oxy) to regulate the polymerization of VAc [10], and the polymerization was proved to be much more complicated and difficult to reproduce [11]. Later, they used another ternary system, CCl4/Fe(OAc)2/PMDETA (PMDETA = N,N,N0 ,N00 ,N00 -pentamethyldiethylenetriamine), but obtained the PVAc with a higher polydispersity (PDI = 1.8–2.0) [12]. The first example of metal-catalyzed radical polymerization of VAc was reported by Sawamoto who employed dicarbonylcyclopentadienyliron dimer [Fe(Cp)(CO)2]2 with an iodide compound as an initiator [13]. Neither NMP or ATRP of VAc has been successful due to the high reactivity of VAc propagation radical, which undergoes radical–radical termination and chain transfer to the methyl group of the acetoxy substituents on the polymer and monomer [3]. Up to date, the best control systems for the CRP of VAc were achieved by degenerative chain transfer in the presence of iodides [14],

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cobalt-mediated radical polymerization [15] and RAFT polymerization using dithiocarbamate [16] and xanthate as RAFT agents [17]. In the past few years, ‘‘click” chemistry, as termed by Sharpless et al. [18,19], has gained most attention for the high specificity, quantitative yields, and near-perfect fidelity. Copper(I)-catalyzed Huisgen dipolar cycloaddition reaction between an azide and an alkyne leading to 1,2,3triazole may be the most popular reaction [20,21]. Recently, several groups have reported the synthesis of a wide range of functional polymers by a coupling procedure using a combination of ATRP and ‘‘click” chemistry. In this process, ATRP was usually the first step since the chain ends of polymers prepared by ATRP can be easily transformed into azides via nucleophilic substitution. Then, the azide end-functionalized polymer can be readily ‘‘clicked” with functional alkynes [22–29]. However, there are some special monomers, such as VAc, which cannot be well polymerized via ATRP but they can be well polymerized via RAFT polymerization. Therefore, the combination of RAFT polymerization and ‘‘click” chemistry is a good choice to synthesize well-defined functional polymers. For example, Wooley and her coworkers obtained block copolymers of acrylic acid and an alkyne-containing monomer by RAFT polymerization. The copolymers were employed to prepare shell-crosslinked micelles, where cores were susceptible to couple with low-molecularweight azides to afford fluorescent nanoparticles [30,31]. Sumerlin’s group synthesized two azido-functionalized RAFT agents and subsequently employed to mediate the RAFT polymerization of styrene and N,N-dimethylacrylamide, and the obtained polymers were coupled with various alkynes to prepare a range of functional telechelics [32]. Our group also obtained well-defined star polymers with hetero-arms, containing three polystyrene and one poly(methyl methacrylate) (PMMA) arms, by the combination of RAFT polymerization, ATRP and ‘‘click” chemistry [33]. In addition, Stenzel and her coworkers synthesized two RAFT agents bearing azide or alkyne moiety in the R group. The RAFT agents were then used in the RAFT polymerization to produce homopolymers of PVAc and poly(styrene) (PS). Combining the PVAc and PS, well-defined block copolymer, poly(styrene)-b-poly(vinyl acetate) (PS-b-PVAc), was successfully obtained by the utility of ‘‘click” chemistry [34]. Very recently, they employed this strategy for the preparation of PVAc comb polymers [35]. Herein, we first synthesized a novel x-azido-functionalized xanthate agent with an azide group in the Z group, namely O-(2-azido-ethyl) S-benzyl dithiocarbonate (AEBDC), and used the new xanthate agent to mediate RAFT polymerization of VAc to give rise to the well-defined PVAc homopolymer with an azido group. Then the resulting x-azido-terminated PVAc was reacted with a fluorescent alkyne, 7-propinyloxy coumarin, to obtain a fluorescent polymer. The fluorescence spectra of 7-propinyloxy coumarin, PVAc prepared via RAFT polymerization using AEBDC as the RAFT agent and the final product after joint PVAc with 7-propinyloxy coumarin were investigated. To the best of our knowledge, this work represents the first synthesis of PVAc with fluorescence.

2. Experimental part 2.1. Materials Sodium azide (Alfa Aesar, 98%, A Johnson Matthey Company), propargyl bromide (Alfa Aesar, 97%, A Johnson Matthey Company), and 7-hydroxy coumarin (Sigma–Aldrich, 98%), n-tetrabutyl ammonium bromide (n-Bu4NBr) (Shanghai Chemical Reagents Co. Ltd, China, 99%) were used as received. Vinyl acetate (VAc) (Shanghai Chemical Reagents Co. Ltd., China, 99%) was purified by passing over a column of basic alumina and subsequently distilled and kept in a refrigerator at 15 °C for short-time store. 2,20 -Azobisisobutyronitrile (AIBN, Shanghai Chemical Reagent Co. Ltd., China, 99%) was recrystallized three times from ethanol. Copper(I) bromide (CuBr) (Chemically pure, Shanghai Chemical Reagent Co. Ltd., China) was purified by washing with acetic acid and acetone, dried under vacuum. N,N,N0 ,N00 ,N00 -pentamethyldiethylenetriamine (PMDETA) (98%, Jiangsu Liyang Jiangdian Chemical Factory, China) was dried with 4 Å molecular sieve and distillated under vacuum. Unless otherwise specified, all other chemicals were purchased from Shanghai Chemical Reagents Co. Ltd. and used as received without further purification. 2.2. Synthesis of RAFT agent O-(2-azido-ethyl) S-benzyl dithiocarbonate (AEBDC) The RAFT agent AEBDC was synthesized by two steps. The synthetic route is shown in Scheme 1. 2.2.1. Synthesis of 2-azidoethanol A mixture of NaN3 (5.13 g, 122 mmol) in water (60 mL), 2-bromoethanol (7.51 g, 60.5 mmol), and n-Bu4NBr (500 mg, 1.5 mmol) was added to a 100 mL flask. The mixture was stirred at 80 °C for 24 h. Then the mixture was extracted with ether (3  70 mL). The combined organic extracts were dried in anhydrous MgSO4 over night and concentrated. Then the crude product was received. 1H NMR (CDCl3): d 3.74 (t, 2H, CH2–OH), 3.45 (t, 2H, CH2– N3). Yield: 73%. 2.2.2. Synthesis of O-(2-azido-ethyl) S-benzyl dithiocarbonate (AEBDC) A mixture of 2-azidoethanol (50 mmol) in DMSO (30 mL), NaOH (50 mmol) water solution was added to a 250 mL flask at room temperature. After stirring for 4 h,

OH Cl

OH 1) NaOH/DMSO

NaN3

2) CS2

N3 S 3) PhCH2Br

N3 O

S

Scheme 1. Synthetic route of the x-azido-functionalized xanthate agent, O-(2-azido-ethyl) S-benzyl dithiocarbonate (AEBDC).

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carbon disulfide (75 mmol) was added dropwise. The reaction mixture was stirred over night at room temperature, and benzyl chloride (50 mmol) was introduced. After 5 h, the reaction mixture was poured into ice water and extracted with ether (3  50 mL). The combined organic extracts were washed with water (2  50 mL). Dried over anhydrous MgSO4 and evaporated to afford a crude product, which was purified by column chromatography on silica gel (petroleum ester as an eluent) to give a yellow liquid (45% yield). 1H NMR(CDCl3): d 3.65 (t, 2H, CH2–N3), 4.42 (s, 2H, CH2–S–), 4.76 (t, 2H, CH2–O–), 7.25–7.40 (m, 5H, CH aro). Elem. Anal. Calcd. (%): C, 47.41; H, 4.38; N, 16.59; Found: C, 47.24; H, 4.55; N, 16.45. 2.3. Synthesis of 7-propinyloxy coumarin A mixture of 7-hydroxy coumarin (20 mmol) in acetone (50 mL), K2CO3 (20 mmol), KI (1 mmol) and propargyl bromide (25 mmol) was added to a flask, and the mixture was stirred over night at 80 °C. Then the reaction mixture was cooled to room temperature and extracted with CH2Cl2 (3  50 mL). The combined organic extracts were washed with water (2  50 mL), dried over anhydrous MgSO4 and evaporated to afford a crude product, which was purified by recrystallization from anhydrous ethanol to give a white solid (75% yield). The synthetic route is shown in Scheme 2. 1 H NMR (CDCl3): d 7.62–7.68 (d, 1H), 7.37–7.63 (d, 1H), 6.88–6.97 (m, 2H), 6.24–6.32 (d, 1H), 4.76–4.80 (d, 2H, CH2–O), 2.55–2.62 (t, 1H).

2.4. RAFT polymerization The procedure of RAFT polymerization of VAc was as follows: a stock solution of 11 mL (119 mmol) of VAc, 450.4 mg (1.78 mmol) of AEBDC, 97.6 mg (0.59 mmol) of AIBN was prepared, and aliquots of 1 mL were placed in each ampoule. The content was purged with argon for 10 min to eliminate the dissolved oxygen. Then the ampoules were flame-sealed and placed in an oil bath held by a thermostat at 80 °C to polymerize. After a preset reaction time, each ampoule was cooled with ice water and opened. The reaction mixture was diluted with a little tetrahydrofuran (ca. 2 mL) and precipitated in a large amount of hexane (ca. 300 mL). The polymer was obtained by filtration and dried at room temperature in vacuum to a constant weight. The conversion of polymerization was determined gravimetrically. 2.5. Click reactions of x-azido-terminated polymers with 7-propinyloxy coumarin The synthetic pathway is shown in Scheme 3. A solution of polymer (PVAc-N3) (0.1 M PVAc-N3 in THF), PMDETA (0.5 equiv), and 7-propinyloxy coumarin (1 equiv) was purged with argon to remove the dissolved oxygen. CuBr (0.5 equiv) was added under argon atmosphere. Then the ampoule was flame-sealed and stirred at 80 °C in the absence of oxygen for 24 h. The reaction mixture was exposed to air, and diluted by THF, then passed through a

propargyl bromide K2CO3 /acetone HO

O

O

O

O

O

Scheme 2. Synthetic route of 7-propinyloxy coumarin.

S N3

O O

S

O

n O

CuBr/PMDETA O

N

N

S

N O

O

S

n O

O

O

O Scheme 3. Synthetic route of postpolymerization with 7-propinyloxy coumarin.

O

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column of neutral alumina. The resultant polymer was precipitated into hexane, filtered and dried under vacuum.

3. Results and discussion 3.1. RAFT polymerization of VAc with AEBDC as a RAFT agent The RAFT polymerizations of VAc using AEBDC as the RAFT agent and AIBN as an initiator at 80 °C were carried out. The results are shown in Figs. 1 and 2, respectively. Fig. 1 shows the kinetic plots of the bulk RAFT polymerization of VAc with [VAc]0:[AEBDC]0:[AIBN]0 = 200:3:1 at 80 °C. The linear relationship between ln([M]0/[M]) and reaction time indicated that the concentration of free radicals in the reaction system remained constant during the process of polymerizations. The dependences of the number-average molecular weight (Mn) and polydispersity index (PDI) on monomer conversions are shown in Fig. 2. The number-average molecular weight (Mn GPC) values

1.8 1.6

ln ([M]0 /[M])

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0

1

2

3 4 Time (h)

5

2.4

Mn ------- Mn th

2.2

PDI

2.0 1.8 1.6

PDI

The number-average molecular weight (Mn) values and polydispersity index (PDI) values of the PVAc were determined with a Waters 1515 gel permeation chromatographer (GPC) equipped with refractive index detector, using HR1, HR3, and HR4 column with molecular weight range 100–500,000 calibrated with poly(methyl methacrylate) (PMMA) standard samples. THF was used as the eluent at a flow rate of 1.0 mL/min operated at 30 °C. 1H NMR spectrum was recorded on an Inova 400 MHz nuclear magnetic resonance instrument, using CDCl3 as a solvent and tetramethyl-silane as the internal standard. The elemental analyses (EA) for C, H, and N were performed on a Leco-CHNS microanalyzer. The purity of products was determined on high-performance liquid chromatograph (HPLC, mode 515, Waters) with the solvent of acetonitrile as eluent at 30 °C. FT-IR spectra were recorded on a Perkin–Elmer 2000 FT-IR spectrometer. The fluorescence spectra were measured by Edinburgh Instruments FLS920.

Mn

2.6. Characterizations

6500 6000 5500 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0

1.4 1.2 1.0 0

20

40 60 Conversion (%)

80

Fig. 2. Dependence of the molecular weights and PDIs on the monomer conversion for the bulk RAFT polymerization of VAc at 80 °C ([VAc]0:[AEBDC]0:[AIBN]0 = 200:3:1).

from GPC results increased almost linearly with monomer conversions and were close to their corresponding calculated values (by Eq. (1)). The polydispersities of the PVAc were relatively low (PDI = 1.22–1.53). However, the PDI values increased to reach 1.5 at high conversion (up to 70%). This phenomenon is likely influenced by the irreversible transfer reactions, such as transfer to the monomer and polymers, which yield both dead chains and new smaller chains and result in the increment of the polydispersity index (PDI). Moreover, the influence of irreversible transfer reactions, especially transfer to polymers, probably amplified by the high viscosity of polymeric solution at high conversions [17d,36]. Mnth ¼

monomer weight  conversion þ M AEBDC mole of AEBDC

ð1Þ

3.2. End group analysis The 1H NMR spectrum of PVAc obtained via RAFT polymerization in the presence of AEBDC is shown in Fig. 3. The results showed the characteristic signals at around 7.05– 7.43 ppm corresponding to the aromatic protons of AEBDC, The characteristic signals at around 3.56–3.80 ppm, 4.60– 4.74 ppm and 2.50–2.74 ppm were assigned to the protons of methylene a, b and c, respectively. These results suggested that the RAFT agent was successfully attached to the polymer chain-end. Furthermore, the molecular weight of PVAc can be calculated from the 1H NMR spectrum (Mn NMR = 3140 g/mol, by Eq. (2)) in Fig. 3, and it was found that the Mn NMR was close to the value obtained by GPC (Mn GPC = 3500 g/mol) and agreed well with the theoretical value (Mn th = 3200 g/mol).    I4:74—5:10 I2:50—2:74  MW VAc þ M nAEBDC ð2Þ Mn ¼ 1 2

6

Fig. 1. Relationship between ln([M]0/[M]) and polymerization time for the bulk RAFT polymerizations of VAc at 80 °C ([VAc]0:[AEBDC]0: [AIBN]0 = 200:3:1).

I2.50–2.74: the integral of the signals (methylene c in the RAFT agent) at 2.50–2.74 ppm; I4.74–5.10: the integral of the signals (methyne d in the PVAc) at 4.74–5.10 ppm.

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g

b

N3

S

g

c

f

R O

d O

a

S

S

n

g g

O

O

g O N3

(i) : R =

e

d

f

e O N (ii) : R =

g

d a

N

e

f

O

N

O

c

O

b

CDCl3 g

b

c

a

2.00

33.57 1.78 1.70

7

6

5

4

3

2

1

0 ppm

Fig. 3. 1H NMR spectrum of PVAc prepared via RAFT polymerization using AEBDC as the RAFT agent. (Solvent: CDCl3, TMS as the internal standard, Mn GPC = 3500 g/mol, PDI = 1.22).

MW VAc : molecular weight of VAc: Thus, all the above evidence showed that AEBDC was an effective RAFT agent for the RAFT polymerization of VAc under these experimental conditions, and PVAc was attached with azide end group with high functionality due to the use of the RAFT agent with azide group in the Z group. 3.3. End group functionalization The obtained x-azido-functionalized PVAc (PVAc-N3) was subsequently involved in ‘‘click” chemistry with 7propinyloxy coumarin to prepare fluorescent polymers. The copper(I) and its ligands were reported [25,37] to be very efficient to catalyze the 1,3-dipolar cycloaddition of organic azides with terminal alkynes. Herein, CuBr/PMDETA was used as the catalytic system, and THF as solvent for the 1,3-dipolar cycloaddition of PVAc-N3 and 7-propinyloxy coumarin at 80 °C. Fig. 4 shows the 1H NMR spectrum recorded for the PVAc-N3 prepared via RAFT polymerization (i) and the product after coupling with 7-propinyloxy coumarin (ii). Compared with Fig. 4i, beside the signals were assigned to the PVAc, neonatal signals at d = 5.26– 5.30 ppm due to the methylene proton (Hb) neighboring the 1,2,3-triazole group, and signals at d = 7.37–7.43 ppm were assigned to the proton of the 1,2,3-triazole ring (Ha) appeared in Fig. 4ii. The characteristic signals at around 6.90–7.00 ppm, 7.63–7.68 ppm, 7.80–7.85 ppm and 6.25– 6.30 ppm in Fig. 4ii were assigned to the protons of the coumarin group. All of these signals confirmed quantitative transformation of PVAc-N3 into the functionalized triazole chain end. Moreover, the success of the ‘‘click” reaction can also be confirmed from FT-IR spectroscopy. In Fig. 5, the IR spectra of PVAc before and after the ‘‘click” reaction showed that the signal at 2100 cm1 (Fig. 5i) as-

fea

(ii)

b

c,d g

(i) 8

7

6

5

4

3

2

1

ppm

0

Fig. 4. 1H NMR spectrum of PVAc (Mn = 3930, PDI = 1.28) prepared via RAFT polymerization using AEBDC as the RAFT agent before (i) and after (ii) coupling with 7-propinyloxy coumarin.

i PVAc-N3 2100

ii PVAc-1,2,3-triazole

800 1650

4500 4000 3500 3000 2500 2000 1500 1000 500

0

Wavenumber cm-1 Fig. 5. FT-IR analysis of the PVAc (Mn = 3930, PDI = 1.28) prepared via RAFT polymerization using AEBDC as the RAFT agent before (i) and after (ii) coupling with 7-propinyloxy coumarin.

signed to the azide group almost disappeared and triazole bands signal at 800, 1650 cm1 (Fig. 5ii) appeared in the polymer after ‘‘click” reaction, indicating higher efficiency of the ‘‘click” reaction between PVAc-N3 and 7-propinyloxy coumarin. 3.4. UV–vis absorption of the polymers Fig. 6 shows the UV–vis spectra of the 7-propinyloxy coumarin, PVAc-N3 and PVAc-1,2,3-triazole, which was obtained by coupling of PVAc-N3 with 7-propinyloxy coumarin, in THF at room temperature. Both of 7-propinyloxy coumarin and PVAc-1,2,3-triazole showed an characteristic UV–vis absorption peak of coumarin moiety at 318 nm.

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0.30

50000

7-propinyloxy coumarin

45000 Fluorescence Intensity (a.u.)

Absorbance (a.u.)

0.25

PVAc-1,2,3-triazole

0.20 0.15 0.10 0.05 0.00 290

300

310

320 330 340 Wavelength (nm)

350

360

-5

i: c = 1*10 mol/L -4

40000

i: c = 2*10 mol/L

35000

iii: c = 2*10 mol/L

-3

-4

30000

iii: c = 1*10 mol/L

25000

iii: c = 2*10 mol/L

20000

iii: c = 1*10 mol/L

15000

ii: c = 1*10 mol/L

-4 -5

-4

10000 5000 0 340 360 380 400 420 440 460 480 500 520 540 Wavelength (nm)

Fig. 6. UV–vis spectra of 7-propinyloxyl coumarin and PVAc-1,2,3-triazole, obtained by coupling of PVAc-N3 with 7-propinyloxy coumarin, in CH2Cl2 at room temperature. The concentration of coumarin moieties is 2  105 mol/L (The concentration of PVAc-1,2,3-triazole with Mn GPC = 4000 g/mol was calculated on the assumption that all of the chain ends of polymers were end-caped with coumarin moieties).

Therefore, the degree of end-functionalized coumarin moiety in PVAc can be measured from the results of UV–vis spectra. The calibration curve was obtained by 7-propinyloxy coumarin in CH2Cl2. Fig. 7 shows the UV–vis standard curve of 7-propinyloxy coumarin in CH2Cl2 at room temperature with the concentrations of coumarin group ranged from 2  106 to 10  106 mol/L. If the ‘‘click” reaction was completely carried out, the concentration of PVAc1,2,3-triazole prepared for the sample with Mn GPC = 4000 g/mol should be 4  106 mol/L. However, the results from Fig. 6 shows that there are about 69% of PVAc-1,2,3triazole (Mn GPC = 4000 g/mol) was end-capped with coumarin moiety. It may be due to the loss of end groups or unperfect ‘‘click” chemistry under these conditions. 3.5. Fluorescence properties of the polymers The fluorescence spectra of 7-propinyloxyl coumarin, PVAc (PVAc-N3) prepared via RAFT polymerization using AEBDC as the RAFT agent and the product (PVAc-1,2,3-triazole) after coupling with 7-propinyloxy coumarin in

Abs.

i: c = 1*10 mol/L

Fig. 8. Fluorescence spectra of (i) 7-propinyloxyl coumarin, (ii) PVAc-N3 prepared via RAFT polymerization using AEBDC as the RAFT agent and (iii) the product (PVAc-1,2,3-triazole with Mn GPC = 4000 g/mol) after coupling with 7-propinyloxy coumarin in CH2Cl2 solution at room temperature, the excitation wavelength was 340 nm. The concentrations are calculated according to the coumarin moieties.

CH2Cl2 solution with different concentrations of coumarin moiety are shown in Fig. 8. It can be observed that both of 7-propinyloxy coumarin and PVAc-1,2,3-triazole, obtained by coupling of PVAc-N3 with 7-propinyloxy coumarin, exhibited a strong fluorescence peak at about 385 nm, and no fluorescence of PVAc-N3 was observed under the same condition. Furthermore, the fluorescence intensity of PVAc-1,2,3-triazole was higher than that of the 7-propinyloxy coumarin with the same concentration of coumarin moiety, indicating a strategy that the fluorescence intensity of polymers can be enhanced by ‘‘click” chemistry method. In the previous study, it was reported that the substitutions at 3- and 7-position of coumarin have strong impact on their fluorescence properties [38,39]. Electrondonating groups at the 7-position of coumarin showed valid enhancement of the fluorescence [40]. In the present work, the electron-donating property of the 1,2,3-triazole ring formed by the ‘‘click” chemistry may enhance the fluorescence intensity of coumarin chromophore [41]. 4. Conclusions A novel strategy endowed the PVAc with fluorescence was demonstrated by combining RAFT polymerization and ‘‘click” chemistry. The process involved (i) the synthesis of a novel x-azido-functionalized PVAc via a RAFT process, and (ii) the ‘‘click” reaction using an alkyne bearing fluorophores. The RAFT process showed that the polymerizations of VAc were controlled. The fluorescence intensity of PVAc can be enhanced after the ‘‘click” reaction in comparison with that of the alkyne. This work presented the first synthesized PVAc with fluorescence, which may extend potential applications of PVAc.

0.12 0.11 0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01

Acknowledgements 1

2

3

4

5 6 7 8 Conc. (mol/L*10-6)

9

10

Fig. 7. UV–vis standard curve of 7-propinyloxyl coumarin.

11

The financial supports of this work by the National Nature Science Foundation of China (No. 20574050), the Science and Technology Development Planning of Jiangsu

F. Chen et al. / European Polymer Journal 44 (2008) 1789–1795

Province (No. BK2007702 and BK2007048), and the Nature Science Key Basic Research of Jiangsu Province for Higher Education (No. 05KJA15008) are gratefully acknowledged.

[16] [17]

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