Synthesis of Well-Defined Polythiol Copolymers by RAFT Polymerization

Article pubs.acs.org/Macromolecules

Synthesis of Well-Defined Polythiol Copolymers by RAFT Polymerization Renaud Nicolay*̈ Matière Molle et Chimie (ESPCI-CNRS, UMR 7167), ESPCI ParisTech, 10 rue Vauquelin, 75005 Paris, France S Supporting Information *

ABSTRACT: A simple methodology to prepare well-defined polythiol copolymers by RAFT polymerization was developed. A methacrylate monomer carrying a S-alkyl-O-ethyl xanthate moiety as thiol protecting group was prepared in two high yield steps. Polythiols were obtained by copolymerizing the functional methacrylate and subsequent aminolysis of the protecting groups. Model reactions and polymerizations showed that the S-alkyl-O-ethyl dithiocarbonate functionality is fully compatible with the RAFT polymerization of methacrylates and did not induce any side reactions. Functionalization of polythiol copolymers was done via thiol−ene addition, Michael addition and thiol−disulfide exchange. Thiol deprotection and functionalization were done in one pot for Michael addition and thiol−disulfide exchange. A complete conversion of thiol groups was observed for all three types of reactions, exemplifying the potential of polythiol copolymers for the preparation of functional materials.

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INTRODUCTION The recent and exponential development of click chemistry1−5 and other efficient functionalization methodologies6−10 has dramatically widened the scope of accessible functional polymers. Among these methodologies, thiol chemistry is of special interest since thiols are capable of reacting to high yields under benign conditions with numerous chemical species including alkyl halides, epoxides, enes, acrylates, ynes, and others.1 As a result, thiol chemistry has been successfully employed for surface and (nano)particle patterning, bioorganic synthesis, polymer modification, imprint nanolithography, fabrication of optical components, hydrogel synthesis, curing of hard protective coatings, self-healing coatings, and many other applications.1,11−15 In addition, the specific interaction of thiols with soft Lewis acids such as gold, silver, cadmium, etc., has been widely used in different areas ranging from microelectronics to biochemistry.16−18 Controlled radical polymerization (CRP) has emerged during the past decade as one of the most robust and powerful techniques for the synthesis of polymeric materials with various topologies (linear, star, comb, (hyper)branched, cyclic, network, etc.), compositions (homopolymer, statistical, gradient, alternating, block, multiblocks, etc.), and functionalities (with almost infinite possibilities regarding the number and nature of functions).19−22 Reversible addition−fragmentation chain transfer (RAFT)23−27 polymerization is one of the most efficient CRP methods, allowing the synthesis of novel (co)polymers with a predetermined degree of polymerization (DP) and low dispersity (Đ = Mw/Mn, where Mw and Mn are the weight- and the number-average molecular weights, respectively), the incorporation of a wide range of functional © 2011 American Chemical Society

monomers, and the preparation of controllable macromolecular structures under mild reaction conditions. Therefore, combining RAFT polymerization and thiol chemistry would allow preparing a variety of macromolecular architectures that could be used as building blocks for the synthesis of functional materials. Unfortunately, what makes thiols so reactive and efficient also makes them very difficult to directly incorporate into polymers. The thiol group is incompatible with most of the polymerization techniques and especially controlled/living polymerizations. Thiols induce side reactions with catalysts and monomers used in living alkene28,29 and living ring-opening metathesis polymerizations30 as well as with monomers and/or active species employed in chaingrowth polycondensation,31 living ring-opening polymerization of heterocyclic monomers,32 living anionic vinyl polymerization,33 and controlled radical polymerization.20 For instance, in the case of radical polymerizations, thiols can react with monomers through radical or Michael additions and will also induce irreversible transfer reactions with propagating radicals. As a result, the work dealing with thiol−ene functionalization almost exclusively relies on polyenes and monothiols.34−40 However, well-defined polythiols would much more versatile building blocks for macromolecular engineering,41 as such polymers would be reactive toward a wide range of functional (macro)molecules, including enes, acrylates, disulfides, alkyl halides, epoxides, and ynes. Received: October 19, 2011 Revised: December 7, 2011 Published: December 20, 2011 821

dx.doi.org/10.1021/ma202344y | Macromolecules 2012, 45, 821−827

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mixture was cooled in an ice−water bath, and a solution of methacryloyl chloride (12.2 mL, 125 mmol) in dry dichloromethane (50 mL) was slowly added while stirring. The mixture was stirred in the cooling bath for 1 h and then at room temperature overnight. Excess of methacryloyl chloride was neutralized with 10 mL of water. The reaction mixture was then successively washed with water (2 × 200 mL), a solution of hydrochloric acid (2 × 200 mL, 0.5 M), a solution of sodium hydroxide (2 × 200 mL, 0.5 M), and brine (200 mL). The organic phase was dried over MgSO4, passed through a column filled with neutral alumina, and concentrated under vacuum to afford 19.4 g (yield = 82.8%) of a yellow liquid. 1H NMR (400 MHz, CDCl3) δ: 6.12 (apparent sextuplet, J = 1 Hz, 1H), 5.58 (quintuplet, J = 1.6 Hz, 1H), 4.65 (q, J = 7.12 Hz, 2H), 4.38 (t, J = 6.44 Hz, 2H), 3.44 (t, J = 6.44 Hz, 2H), 1.94 (dd, J = 1 Hz and J = 1 Hz, 3H), 1.42 (t, J = 7.12 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ: 213.8, 167.1, 136.1, 126.2, 70.4, 62.3, 34.5, 18.4, 13.9. Synthesis of S-Propyl-O-ethyl Dithiocarbonate, 2. A 500 mL round-bottomed flask equipped with a dropping funnel was charged with a magnetic stirring bar, potassium ethyl xanthogenate (21 g, 131 mmol), and acetone (150 mL). A solution of 1-bromopropane (14.0 g, 114 mmol) in acetone (50 mL) was added dropwise at room temperature over a period of 60 min. Stirring was continued overnight at room temperature. Solids were removed by filtration to afford a clear pale yellow solution. The solids on the funnel were washed with acetone (total of 75 mL). The combined washing and filtrate solutions were concentrated under vacuum to furnish a yellow viscous liquid that was dissolved in dichloromethane (200 mL). This solution was washed twice with water (150 mL), and the organic phase was dried over MgSO4 and evaporated to dryness to afford 17.2 g (91.7%) of a pale yellow liquid. 1H NMR (400 MHz, CDCl3) δ: 4.62 (q, J = 7.12 Hz, 2H), 3.08 (t, J = 7.3 Hz, 2H), 1.70 (apparent sextuplet, J = 7.32 Hz, 2H), 1.40 (t, J = 7.12 Hz, 3H), 1.00 (t, J = 7.38 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ: 215.3, 69.8, 37.8, 21.9, 13.9, 13.5. General Procedure for the RAFT Polymerization of Monomer 1. In a typical experiment, 2-cyano-2-propyl benzodithioate (CPBDT) (3.26 mg, 1.47 × 10−5 mol), 2,2′-azobis(2methylpropionitrile) (AIBN) (2.42 × 10−1 mg, 1.47 × 10−6 mol), monomer 1 (622 mg, 2.65 × 10−3 mol), and anisole (0.175 mL) were charged in a flask. The flask was deoxygenated by bubbling N2 for 30 min and placed in an oil bath thermostated at 65 °C for 15 h. The reaction was stopped by placing the flask in an ice−water bath, and the polymer was isolated by precipitation in diethyl ether. General Procedure for RAFT Copolymerization of MMA, BMA, and Monomer 1. In a typical experiment, MMA was purified by passing through a basic alumina column and then bubbled with N2 for 30 min. 2-Cyano-2-propyl benzodithioate (CPBDT) (25.9 mg, 1.17 × 10−4 mol), 2,2′-azobis(2-methylpropionitrile) (AIBN) (1.92 mg, 1.17 × 10−5 mol), monomer 1 (682 mg, 2.91 × 10−3 mol), and anisole (0.75 mL) were charged in a flask. The flask was deoxygenated by bubbling N2 for 30 min. MMA (2 mL, 18.7 × 10−3 mol) was added, and the flask was placed in an oil bath thermostated at 65 °C for 24 h. Samples were withdrawn periodically under a N2 atmosphere for monomer conversion and molecular weight determination. The reaction was stopped by placing the flask in an ice−water bath. A pink polymer was isolated by precipitation in methanol or diethyl ether. General Procedure for Polythiol Copolymers Deprotection. In a typical experiment, the protected copolymer, P2 (Mn,th = 21 000; 25 xanthate functions per chain) (420 mg, 0.5 mmol of thiocarbonyl moieties), was introduced in a flask placed under a nitrogen atmosphere. THF (3 mL) was added, and after complete dissolution of the polymer, butylamine (91.4 mg, 1.25 mmol, 2.5-fold molar excess with respect to the thiocarbonyl moiety) and traces of reducing agent, tributylphosphine, were added to the solution. The reaction mixture was stirred for 1.5 h at room temperature. During this period, the originally pink solution became pale yellow. A white polymer, P7 (Mn = 16 100; Mw/Mn = 1.18), was recovered by precipitation in diethyl ether. General Procedure for Thiol−Ene Addition. In a typical experiment, the polythiol copolymer, P7 (Mn,th = 18 700, 25 functions

Despite numerous reports on the synthesis of polymers containing thiol functional groups,42−57 the synthesis of wellcontrolled polymers with a defined number of mercapto groups remains challenging. The difficulty in preparing such polymers is that the typical polymerization and functionalization conditions give side reactions and/or moderate yields.14,51−57 Therefore, the search for a simple synthetic procedure that would allow synthesizing well-controlled polythiols is still an ongoing effort. In the present work, a very simple and efficient methodology to prepare well-defined (block) copolymers incorporating thiol side groups is reported. Polythiol copolymers were prepared by copolymerizing a methacrylate monomer carrying a protected thiol, via RAFT polymerization, and then deprotecting the thiol functionality of the copolymers. The S-alkyl-O-ethyl xanthate moiety used as thiol protecting group proved to be fully compatible with the RAFT polymerization of methacrylates and did not induce any side reactions. In addition, thiol deprotection could be done under very mild conditions, e.g., aminolysis at room temperature, which allowed deprotection and functionalization to be performed in a one-pot process. To exemplify the versatility of polythiol copolymers as building blocks for macromolecular engineering, polythiol copolymers were quantitatively functionalized through thiol−ene addition, Michael addition, and thiol−disulfide exchange.

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EXPERIMENTAL SECTION

Materials. Butyl methacrylate (BMA, 99%) and methyl methacrylate (MMA, 99%) were purified by passing through a column filled with basic alumina to remove the inhibitors or antioxidants. Unless otherwise noted, reagents were commercially available and used without further purification. Analyses. Ultraviolet (UV) light irradiation was carried out with two UVGL-55 UV lamps at a wavelength of 365 nm. 1H and 13C NMR spectra were recorded at 297 K on a Bruker AVANCE 400 spectrometer at 400 and 100 MHz, respectively, and referenced to the residual solvent peaks (1H, δ 7.26 for CDCl3; 13C, δ 77.16 for CDCl3). Monomer conversions were determined by 1H NMR. Molecular weights and dispersities were determined by size exclusion chromatography (SEC). SEC analyses were conducted with a Waters 590 pump and a Waters R410 refractive index detector using three thermostated styragel columns set (two HT6E and one HT2) in THF as eluent at 40 °C and at a flow rate of 1 mL min−1. The apparent molecular weights (Mn,SEC and Mw,SEC) and dispersities (Mw/Mn) were determined with a calibration based on polystyrene standards. The spectroscopic measurements were performed on a UV-2401PC (Shimadzu Corp.) UV/vis spectrometer. Synthesis of S-2-Hydroxyethyl-O-ethyl Dithiocarbonate. A 500 mL round-bottomed flask equipped with a dropping funnel was charged with a magnetic stirring bar, potassium ethyl xanthogenate (53.8 g, 336 mmol), and acetone (210 mL). A solution of 2bromoethanol (34.5 g, 276 mmol) in acetone (90 mL) was added dropwise at room temperature over a period of 60 min. Stirring was continued overnight at room temperature. Solids were removed by filtration to afford a clear pale yellow solution. The solids on the funnel were washed with acetone (total of 150 mL). The combined washings and filtrate were concentrated under vacuum to furnish a yellow solid that was dissolved in chloroform (500 mL). This solution was washed three times with brine (250 mL), dried over MgSO4, and evaporated to dryness to afford 41.9 g (91.3%) of a yellow liquid. 1H NMR (400 MHz, CDCl3) δ: 4.59 (q, J = 7.12 Hz, 2H), 3.79 (t, J = 6.3 Hz, 2H), 3.27 (t, J = 6.3 Hz, 2H), 3.17−2.88 (broad peak, 1H, OH), 1.36 (t, J = 7.12 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 214.4, 70.2, 60.4, 38.2, 13.7. Synthesis of Monomer 1. S-2-Hydroxyethyl-O-ethyl dithiocarbonate (16.6 g, 100 mmol) and triethylamine (18.1 mL, 130 mmol) were dissolved in dry dichloromethane (125 mL). The reaction 822


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Scheme 1. (A) Preparation of Functional Monomer 1; (B) Preparation of Model Xanthate 2; (C) RAFT Copolymerization of 1 with MMA

thiol per chain) (94 mg, 0.125 mmol of thiol moieties), and 2,2dimethoxy-2-phenylacetophenone (DMAP) (16 mg, 62.5 × 10−3 mmol) were introduced in a vial placed under a nitrogen atmosphere. Deoxygenated anisole (1 mL) was added, and after complete dissolution of the polymer, 4-allylanisole (92.6 mg, 0.625 mmol, 5fold molar excess with respect to the thiol moiety) was added to the solution. UV irradiation at 365 nm was carried for 1 h at room temperature. A white polymer, P11 (Mn = 18 800; Mw/Mn = 1.24), was recovered by precipitation in diethyl ether. General Procedure for Michael Addition. In a typical experiment, the protected copolymer, P2 (Mn,th = 21 000; 25 xanthate functions per chain) (210 mg, 0.25 mmol of thiocarbonyl moieties), was introduced in a flask placed under a nitrogen atmosphere. THF (2 mL) was added, and after complete dissolution of the polymer, butylamine (45.7 mg, 0.625 mmol, 2.5-fold molar excess with respect to the thiocarbonyl moiety) and traces of reducing agent, tributylphosphine, were added to the solution. The reaction mixture was stirred for 1.5 h at room temperature (under a nitrogen atmosphere). During this period, the originally pink solution became pale yellow. Benzyl acrylate (185 mg, 1.25 mmol, 5-fold molar excess with respect to the thiocarbonyl moiety) was added to the reaction mixture which was stirred overnight at room temperature. A yellow polymer, P12 (Mn = 28 500; Mw/Mn = 1.15), was recovered by precipitation in diethyl ether. General Procedure for Thiol−Disulfide Exchange. In a typical experiment, the protected copolymer, P2 (Mn,th = 21 000; 25 xanthate functions per chain) (52.5 mg, 6.25 × 10−2 mmol of thiocarbonyl moieties), and 2,2′-dipyridyl disulfide (688 mg, 3.12 mmol, 50-fold molar excess with respect to the thiocarbonyl moiety) were dissolved in THF (1.5 mL). Butylamine (11.4 mg, 0.156 mmol, 2.5-fold molar excess with respect to the thiocarbonyl moiety) was added. The pink solution immediately turned to yellow. The reaction mixture was stirred overnight at room temperature. A white polymer, P13 (Mn = 24 000; Mw/Mn = 1.22), was recovered by precipitation in diethyl ether or methanol.

prepared in two simple steps with an overall yield of 76% (Scheme 1A). In order to demonstrate that the xanthate moiety used as thiol protecting group does not induce transfer reactions during the polymerization of methacrylates, a model molecule, 2, was synthesized (Scheme 1B). Methyl methacrylate (MMA) was then polymerized by RAFT in the presence of this model compound. The polymerization was conducted at 65 °C, using 2-cyano-2-propyl benzodithioate (CPBDT) as CTA and a ratio [MMA]0/[2]0/[CPBDT]0/[AIBN]0 of 200/200/1/0.2. The polymerization showed the typical features of a controlled radical polymerization (CRP), i.e., a constant concentration of propagating radicals with first-order kinetics in monomer and a linear evolution of molecular weight (MW) with conversion (Figure 1). After 22 h of reaction, a well-defined polymer, P1,

Figure 1. Kinetics, Mn, and Mw/Mn vs conversion plots for the RAFT polymerization of MMA in the presence of xanthate 2. [MMA]0/[2]0/ [CPBDT]0/[AIBN]0 = 200:200:1:0.2, MMA/anisole = 5:3 (v/v), 65 °C.

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RESULTS AND DISCUSSION Synthesis of Functional Monomer, 1. Dithiocarbonates, commonly called xanthates, are common chain transfer agents (CTAs) for the RAFT polymerization of nonconjugated monomers.25,26,58 However, it was recently demonstrated that xanthates can be designed to be inactive toward radical generated from conjugated monomers, such as methacrylates, styrenics, or even more reactive acrylates.59−62 In addition, thiols can easily be obtained by aminolysis of dithiocarbonyl moieties such as xanthates.48−50 Therefore, a methacrylate monomer containing a xanthate as thiol protecting group was

with Mn = 16 100 (Mn,th = 16 800) and Mw/Mn = 1.13, was obtained. The very good agreement between theoretical and experimental molecular weights is consistent with the absence of transfer reactions to model xanthate 2 during the polymerization. Transfer to model xanthate 2 would generate new polymer chains and would cause a discrepancy (toward lower mass) between experimental and theoretical molecular weights. 823


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To further confirm that xanthate 2 did not induce transfer reactions during MMA polymerization, P1 was analyzed by 1H NMR and UV spectroscopy. The 1H NMR spectrum of P1 did not show any peak around 4.6 ppm that would be characteristic of protons in the α-position of the oxygen of the xanthate. On the other hand, three peaks at 7.82, 7.46, and 7.30 ppm confirmed the presence of the dithiobenzoate chain-end on P1 (Figure 2).

MW with conversion were observed for all polymerizations, yielding well-defined copolymers with low dispersities (Figure

Figure 4. Kinetics, Mn, and Mw/Mn vs conversion plots for the RAFT copolymerization of 1 and MMA, P3. [MMA]0/[1]0/[CPBDT]0/ [AIBN]0 = 120:55:1:0.1, anisole 20% (in volume), 65 °C.

4). Moreover, a DP of 1000 was targeted to exemplify that high-MW functional copolymers can be prepared with monomer 1. A well-defined copolymer with Mn = 77 600 (Mn,th = 72 500) and Mw/Mn = 1.25 was obtained. In every case, a drift of the composition in the final copolymer was observed, as compared to the initial ratio of monomers (Table 1). This drift of composition indicates that 1 was incorporated slightly faster than MMA into the polymer chains. Monomer 1 was also homopolymerized using a ratio [1]0/[CPBDT]0/ [AIBN]0 of 180/1/0.1. A well-defined polymer, with Mn = 51 000 and Mw/Mn = 1.08 (monomer conversion of 97.4%; Mn,th = 41 400), was obtained after 15 h of polymerization at 65 °C. The retention of chain-end functionality is one of the key features of CRP. To confirm the presence of the dithiobenzoate chain-end on copolymers prepared with monomer 1, a block copolymer was synthesized using P2 as macroCTA and 2,2′azobis(N-butyl-2-methylpropionamide) (VAm-110) as radical initiator. A well-defined high MW block copolymer, P6, with Mn = 145 000 (Mn,th = 165 000) and Mw/Mn = 1.25, was obtained by polymerizing 2000 equiv of butyl methacrylate (BMA) at 80 °C. No unreacted macroCTA could be detected by SEC, demonstrating very high chain-end functionality for copolymer P2 (Figure 5). Well-defined polythiols, P7−P10, were prepared by aminolysis at room temperature of the protected copolymers, P2−P5 (Scheme 2A and Table 2). The quantitative deprotection of thiol groups was confirmed by 1H NMR, 13C NMR, and UV−vis spectroscopy. Before deprotection, peaks at 4.65 (a), 4.15 (b), and 3.40 (d) ppm corresponding to the protected thiols were observed by 1H NMR (Figure 6). After deprotection, the peak (a) corresponding to the protons in α position of the oxygen of the xanthate completely disappeared.

Figure 2. 1H NMR spectrum in CDCl3 of PMMA, P1, prepared in the presence of xanthate 2. [MMA]0/[2]0/[CPBDT]0/[AIBN]0 = 200:200:1:0.2, MMA/anisole = 5:3 (v/v), 65 °C, 22 h. Polymer isolated by precipitation in diethyl ether.

UV/vis spectroscopy showed the presence of the dithiobenzoate chain-end (peak at 306 nm) and also confirmed the complete absence of xanthate group (no peak at 282 nm) on P1 (Figure 3). All these results clearly demonstrate that the S-

Figure 3. UV/vis spectra of P1 (1 × 10−4 M in DMF), xanthate 2 (4 × 10−4 M in DMF), and CPBDT (1 × 10−4 M in DMF).

alkyl-O-ethyl dithiocarbonate functionality did not induce any side reactions during the RAFT polymerization of MMA. The functional monomer 1 and MMA were copolymerized by RAFT using CPBDT as CTA (Scheme 1A). Different ratios of 1/MMA were used, while keeping a targeted DP of ∼180 (Table 1, P2−P4). First-order kinetics and linear evolutions of Table 1. RAFT Copolymerization of 1 with MMAa P2 P3 P4 P5

[MMA]0/[1]0

time (h)

86.7/13.3 68.4/31.6 49.1/50.9 84.7/15.3

24 24 16 43

conv (%)b

Mn,SEC

Mw/Mn

MMA/1 in polymc

95.2; 89.3; 66.2; 58.8;

18 800 26 800 31 100 77 600

1.15 1.29 1.30 1.25

85.5/14.5 65.9/34.1 44.2/55.8 81.2/18.8

96.6 94.4 77.9 62.0

Anisole 20% (in volume) at 65 °C; [CPBDT]0/[AIBN]0 = 1:0.1; targeted DP = ([MMA]0 + [1]0)/[CPBDT]0: P2 = 185, P3 = 175, P4 = 200, P5 = 1000. bConversion of MMA and 1, respectively. cDetermined by 1H NMR. a

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Table 2. Synthesis of Polythiol Copolymersa P7 P8 P9 P10

precursor

Mn,SEC

Mw/Mn

thiol/chainb

P2 P3 P4 P5

16 100 28 400 25 100 66 900

1.18 1.27 1.35 1.33

26 53 82 96

a

Thiol deprotection carried out in THF at RT for 1.5 h; 2.5 equiv of butylamine with respect to thiol groups, traces of tributylphosphine. b Determined by 1H NMR.

Three model reactions relying on thiol−ene radical addition, thiol Michael addition, and thiol−disulfide exchange were performed on the polythiol copolymer P7 and on the protected polythiol copolymer P2 (Scheme 2 and Table 3). A complete functionalization of the thiol moieties was observed by 1H NMR for all three types of reactions (Figure 7 and Figures S10 and S11). The efficiency of the deprotection and functionalization reactions under these mild conditions is in good agreement with previous reports on thiol chemistry.14,63,64 For example, in the case of the thiol Michael addition, the peak (c) corresponding to the protons in α position of the oxygen of the xanthate protecting group completely disappeared after functionalization, while peaks corresponding the benzyl moiety

Figure 5. SEC trace of P2-b-PBMA block copolymer, P6, prepared by RAFT polymerization of BMA with P2 as macroCTA. [BMA]0/ [P2]0/[VAm-110]0 = 2000:1:1, BMA/anisole = 1:3 (v/v), 73 h at 80 °C.

On the other hand, peaks (b′ and d′) from the ethyl linker could be observed and were shifted toward the high field region (Figure 6). The complete absence of thiocarbonyl (no peak at 214 ppm) and xanthate groups (no peak at 282 nm) on the deprotected polythiol copolymers was also confirmed by 13C NMR and UV−vis spectroscopy, respectively (Figures S1−S9).

Scheme 2. (A) Synthesis of Polythiol Copolymers and Their Subsequent Functionalization via Thiol−Ene Chemistry; (B) OnePot Deprotection and Functionalization, through Michael Addition and Thiol−Disulfide Exchange, of Protected Polythiol Copolymers

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polymerization of methacrylates. Well-defined protected polythiol copolymers and block copolymers were prepared. Polythiol copolymers were subsequently obtained by simple aminolysis of the xanthate protecting groups at room temperature. Functionalization of polythiol copolymers was done via thiol−ene addition, Michael addition, and thiol− disulfide exchange. A complete conversion of thiol groups was observed for all three types of reactions. Thanks to the mild conditions used for the removal of the xanthate protecting group, thiol deprotection and functionalization were done in one pot for Michael addition and thiol−disulfide exchange. The simplicity and efficiency of the reported procedure, coupled with the great potential of CRP and thiol chemistry, should allow using polythiol (co)polymers as versatile building blocks for the preparation of a wide range of functional materials.

Figure 6. 1H NMR spectra (zoomed in between 2.5 and 5 ppm) in CDCl3 of protected copolymer P2 and polythiol copolymer P7.

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b

P11 P12c P13d

precursor

reagent

Mn,SEC

P7 P2 P2

4-allylanisole benzyl acrylate 2,2′-dithiodipyridine

18 800 28 500 24 000

S

1 H NMR, 13C NMR, and UV spectra. This material is available free of charge via the Internet at http://pubs.acs.org.

Mw/Mn conv (%)a 1.24 1.15 1.22

ASSOCIATED CONTENT

* Supporting Information

Table 3. Functionalization of Polythiol Copolymers

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100 100 100

a

AUTHOR INFORMATION

Corresponding Author

Conversion obtained from the disappearance of the thiol (or protected thiol) peak by 1H NMR and the appearance of peaks corresponding to the product. bIrradiation at 365 nm for 1 h at RT in anisole; SH/4-allylanisole/DMAP = 1:5:0.5. cOvernight in THF at RT; benzyl acrylate added after 1.5 h; SH/butylamine/benzyl acrylate = 1/2.5/5. dOvernight in THF at RT; SH/butylamine/2,2′dithiodipyridine = 1/2.5/50.

*E-mail: [email protected].

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ACKNOWLEDGMENTS The author is grateful to ESPCI and CNRS for financial support. The author thanks the members of the Matière Molle et Chimie laboratory for their valuable help. Prof. Ludwik Leibler and Dr. Ilias Iliopoulos are especially acknowledged for many stimulating and extremely helpful discussions.

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REFERENCES

(1) Hoyle, C. E.; Lowe, A. B.; Bowman, C. N. Chem. Soc. Rev. 2010, 39, 1355−1387. (2) Iha, R. K.; Wooley, K. L.; Nystrom, A. M.; Burke, D. J.; Kade, M. J.; Hawker, C. J. Chem. Rev. 2009, 109, 5620−5686. (3) Hoyle, C. E.; Bowman, C. N. Angew. Chem., Int. Ed. 2010, 49, 1540−1573. (4) Kade, M. J.; Burke, D. J.; Hawker, C. J. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 743−750. (5) Hoogenboom, R. Angew. Chem., Int. Ed. 2010, 49, 3415−3417. (6) Theato, P.; Kim, J.-U.; Lee, J.-C. Macromolecules 2004, 37, 5475− 5478. (7) Theato, P. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 6677− 6687. (8) Nicolay, R.; Marx, L.; Hemery, P.; Matyjaszewski, K. Macromolecules 2007, 40, 9217−9223. (9) Fu, Q.; Lin, W.; Huang, J. Macromolecules 2008, 41, 2381−2387. (10) Kulis, J.; Bell, C. A.; Micallef, A. S.; Jia, Z.; Monteiro, M. J. Macromolecules 2009, 42, 8218−8227. (11) Ryu, J.-H.; Jiwpanich, S.; Chacko, R.; Bickerton, S.; Thayumanavan, S. J. Am. Chem. Soc. 2010, 132, 8246−8247. (12) Oh, J. K.; Siegwart, D. J.; Lee, H.-i.; Sherwood, G.; Peteanu, L.; Hollinger, J. O.; Kataoka, K.; Matyjaszewski, K. J. Am. Chem. Soc. 2007, 129, 5939−5945. (13) Yuan, Y. C.; Rong, M. Z.; Zhang, M. Q.; Chen, J.; Yang, G. C.; Li, X. M. Macromolecules 2008, 41, 5197−5202. (14) Ghosh, S.; Basu, S.; Thayumanavan, S. Macromolecules 2006, 39, 5595−5597. (15) Wong, L.; Boyer, C.; Jia, Z.; Zareie, H. M.; Davis, T. P.; Bulmus, V. Biomacromolecules 2008, 9, 1934−1944. (16) Trollss, M.; Hawker, C. J.; Hedrick, J. L.; Carrot, G.; Hilborn, J. Macromolecules 1998, 31, 5960−5963.

Figure 7. 1H NMR spectra (zoomed in between 2.35 and 7.85 ppm) in CDCl3 of protected copolymer P2 and functional copolymer P12.

were observed by 1H NMR (Figure 7). In addition, for the Michael addition and the thiol−disulfide exchange, deprotection and functionalization were done in one-pot directly from the protected copolymer P2. These results illustrate the versatility and potential of (protected) polythiol copolymers as precursors for the synthesis of functional polymers.

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CONCLUSION In summary, a very simple methodology to prepare welldefined polythiol copolymers by RAFT polymerization is reported. This approach relies on the use of S-alkyl-O-ethyl dithiocarbonate as thiol protecting group. Model reactions and polymerizations demonstrate that the xanthate protecting group does not induce any side reactions during the RAFT 826


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