Hybridization of CMRP and ATRP: A Direct Living Chain Extension

Article pubs.acs.org/Macromolecules

Hybridization of CMRP and ATRP: A Direct Living Chain Extension from Poly(vinyl acetate) to Poly(methyl methacrylate) and Polystyrene Ya-Jo Chen,† Bing-Jyun Wu,† Fu-Sheng Wang,† Mu-Huan Chi,‡ Jiun-Tai Chen,*,‡ and Chi-How Peng*,† †

Department of Chemistry and Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, 101, Sec 2, Kuang-Fu Rd., Hsinchu 30013, Taiwan ‡ Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan

Downloaded by CENTRAL MICHIGAN UNIV on September 14, 2015 | http://pubs.acs.org Publication Date (Web): September 14, 2015 | doi: 10.1021/acs.macromol.5b01101

S Supporting Information *

ABSTRACT: Cobalt-mediated radical polymerization (CMRP) was used to prepare well-defined poly(vinyl acetate) (PVAc) as the macroinitiator in the reverse atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and styrene (Sty) for the synthesis of block copolymers of PVAc-b-PMMA and PVAc-b-PSty with linearly increased molecular weight and smoothly shifted gel permeation chromatography (GPC) traces. The chain extension from PVAc to PMMA or PSty via the hybridization of CMRP and ATRP required neither a difunctional initiator nor further chain-end modification and was as simple as regular chain extension in the reverse ATRP process. Because the cobalt complex bonded to the chain end of PVAc was dissociated during the ATRP process, this method also efficiently solved the issue of metal removal in the CMRP process.

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INTRODUCTION Cobalt-mediated radical polymerization (CMRP)1−5 has been recognized among various controlled/living radical polymerization (C/LRP)6−13 methods because of its highly efficient control process to vinyl acetate and other “inactive monomers”;9 however, the mediation for the polymerization of the commodity monomers, such as methyl methacrylate or styrene, which are categorized as “active monomers”,14 remains a challenge for CMRP.15,16 Alternatively, although atom transfer radical polymerization (ATRP),17−22 one of the most developed C/LRP methods, has been applied to many vinyl monomers, the polymerization of vinyl acetate still cannot be well controlled by the ATRP process.23,24 A similar situation has also been encountered by other C/LRP methods; most of the methods or agents can mediate the C/LRP of only one type (either active or inactive) of vinyl monomer.25−29 Thus, the block copolymers of active and inactive monomers were synthesized using difunctional initiators30−32 or chain-end modification of the first block polymer,33−36 which require additional synthetic processes and purifications. In this work, we successfully obtained the block copolymers of poly(vinyl acetate)-b-poly(methyl methacrylate) (PVAc-b-PMMA) and poly(vinyl acetate)-b-polystyrene (PVAc-b-PSty) via the reverse ATRP process using controlled poly(vinyl acetate) with a cobalt(III) chain end prepared by the CMRP as a radical initiator. The linearly increased molecular weight with conversion and smoothly shifted gel permeation chromatog© XXXX American Chemical Society

raphy (GPC) traces were observed during the chain growth of the second block. The polymeric products were precipitated as a white powder, indicating the absence of metal complexes, and then hydrolyzed to form amphiphilic block copolymers able to undergo micellization to further demonstrate the formation of block copolymers.

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RESULTS AND DISCUSSION

System Design Based on an Understanding of the Mechanism. Theoretically, the direct chain extension from PVAc to PMMA or PSty can be achieved via the reverse ATRP of MMA or Sty initiated by a PVAc macroinitiator formed from the CMRP (Scheme 1) if the CMRP and ATRP systems are properly selected. The CMRP of vinyl acetate was reported to be mediated via degenerative transfer (DT) by cobalt porphyrin and cobalt salen complexes (eq a)37−39 and via reversible termination (RT) by cobalt acetylacetonate (CoII(acac)2) at a relatively high temperature (eq b).40,41 Herein, we chose CoII(acac)2 to prepare PVAc macroinitiators (CoIII-PVAc) that can generate PVAc radicals by self-dissociation because the external radical source required by the DT process38,42,43 could also initiate new polymer chains during the subsequent ATRP process. The copper complex of CuII(bpy)2Br2 was first Received: May 21, 2015 Revised: August 31, 2015

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DOI: 10.1021/acs.macromol.5b01101 Macromolecules XXXX, XXX, XXX−XXX

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Scheme 1. Proposed Mechanism for the Hybridization of CMRP and ATRP That Could Generate the Block Copolymer of PVAc-b-PMMA

selected to mediate the reverse ATRP for chain extension of the PMMA block because the system with a smaller KATRP value would retain a lower radical concentration, thereby driving the CoII/CoIII-PVAc equilibrium (eq b) to the CoII side. Thus, this system could minimize the residual CoIII-PVAc. Chain Extension from CoIII-PVAc to PMMA. The macroinitiator of CoIII-PVAc was synthesized by following the previously reported CMRP process,44 with a slightly modified condition of [CoII(acac)2]0/[AIBN]0/[VAc]0 = 1/3/700 in bulk at 60 °C to obtain the polymeric product with Mn equal to 9800 g/mol and Mw/Mn (PDI) equal to 1.19 after 240 min (Figure S1). The chain extension was then performed with the typical reverse ATRP condition45−47 as [CoIII-PVAc]0/ [CuBr2]0/[bpy]0/[MMA]0 = 1/2/4.4/2000 in benzene with [MMA]0 = 4.0 M at 60 °C. The MMA polymerization followed a first-order kinetic process to reach 80% monomer conversion in 20 h with a linearly increasing molecular weight and gradually decreasing Mw/Mn values versus conversion (Figure 1). The solution turned from dark green to yellow during the polymerization, suggesting the transformation from organocobalt(III) and copper(II) species to cobalt(II) and copper(I) complexes. A white polymer powder product was obtained by precipitation in methanol after the column chromatography and had a molecular weight of 60700 and an Mw/Mn value of 1.38, with a PVAc/PMMA ratio of approximately 9800/50900 (Table 1, entry 1). To our knowledge, this result is the first example of direct chain extension from PVAc to PMMA that required neither chain-end modification nor a difunctional initiator, showing the living characteristics of Mn increasing linearly with conversion and a narrow molecular weight distribution. Furthermore, this method also provided an efficient route for the removal of the cobalt chain end from the polymers. Although the controlled block copolymer of PVAc-b-PMMA was obtained via the first hybridization of CMRP and ATRP, the bimodal GPC traces observed during the polymerization and the molecular weight deviation indicated that the chain extension process could be further optimized. The addition of copper wire, which was reported to positively affect the equilibrium of Cu(I) and Cu(II) species and thus enhance the control efficiency of ATRP,48 was applied to our system and indeed improved the chain extension process. The reverse ATRP initiated by CoIII-PVAc with 1 cm of Cu(0) wire showed a faster MMA polymerization approaching 44% conversion in 7

Figure 1. Reverse ATRP of MMA initiated by PVAc macroinitiator (Mn = 9800 g/mol, Mw/Mn = 1.19) in benzene at 60 °C with the condition of [CoIII-PVAc]0/[CuBr2]0/[bpy]0/[MMA]0 = 1/2/4.4/ 2000, [MMA]0 = 4.0 M. (a) Plots of Mn and Mw/Mn (PDI) versus conversion; (b) evolution of GPC traces.

h and generated the polymeric product with a higher molecular weight of 109700 but a slightly increased Mw/Mn value of 1.69 (Table 1, entry 2). The molecular weight deviation and bimodal GPC traces were also significantly diminished (Figure 2). The increasing polymerization rate is attributed to the reduction of Cu(II) complexes by Cu(0) wire, which provides another route for the generation of more Cu(I) species that act as an activator in the ATRP process. The attempt to narrow the molecular weight distribution by lowering the temperature was not successful. The chain extension became slower at 40 °C, with a positive molecular weight deviation and higher Mw/Mn value of 2.11 (Table 1, entry 3). The GPC traces illustrated that the macroinitiators of CoIII-PVAc may not even react completely (Figure S4). This result should be attributed to the declined initiation efficiency of CoIII-PVAc caused by the lowered temperature. Alternatively, increasing the temperature to 75 °C led to a more rapid chain extension, which reached 65% conversion after 4 h, with a negative molecular weight deviation and Mw/Mn value as high as 1.71 (Table 1, entry 4). However, the molecular weight increased only slightly after 40% conversion, suggesting the formation of terminated chains (Figure S5). Thus, the proper reaction temperature, which is sufficiently high for the dissociation of CoIII-PVAc within a reasonable time but can still ensure a low radical concentration to minimize the influence of termination reaction, was critical for the hybridization of CMRP and ATRP. The ligand is one of the most important factors determining the performance of ATRP.49−52 In addition to bpy, two ATRP ligands, PMDETA and Me6TREN, were also used in the chain extension process to evaluate the ligand effect. Replacing the ligand from bpy to PMDETA, which was reported to form the copper complex with a higher KATRP value, led to a chain B


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Table 1. Direct Chain Extension from PVAc Macroinitiator Prepared by the CMRP to PMMA Obtained from Reverse ATRP entry 1 2 3 4 5 6 7 8 9 10


11

reactants III

[Co -PVAc]0/[CuBr2]0/[bpy]0/[MMA]0 = 1/2/4.4/2000 [CoIII-PVAc]0/[CuBr2]0/[bpy]0/[MMA]0/Cu(0) = 1/2/4.4/2000/1 cm

[CoIII-PVAc]0/[CuBr2]0/[PMDETA]0/[MMA]0/Cu(0) = 1/2/2.2/2000/1 cm [CoIII-PVAc]0/[CuBr2]0/[Me6TRAN]0/[MMA]0/Cu(0) = 1/2/2.2/2000/1 cm [CoIII−PVAc]0/[MMA]0 = 1/2000 [CoIII-PVAc]0/[CuBr2]0/[bpy]0/[Sty]0/Cu(0) = 1/2/4.4/2000/1 cm [CoIII-PVAc]0/[CuBr2]0/[PMDETA]0/[Sty]0/Cu(0) = 1/2/2.2/2000/1 cm [CoIII-PVAc]0/[CuBr2]0/[Me6TREN]0/[Sty]0/Cu(0) = 1/2/2.2/2000/1 cm [CoIII-PVAc]0/[Sty]0 = 1/2000

temp (°C)

time (min)

conva (%)

Mn,GPCb (g/mol)

Mn,thc (g/mol)

Mw/Mnb

60 60 40 75 60

1200 420 720 240 480

80 44 26 65 56

60700 109700 222900 38200 105400

170100 97000 61600 142500 123400

1.38 1.69 2.11 1.71 1.42

60

960

53

74000

114900

1.35

60 60 60

300 3000 2610

44 38 40

114400 86500 48500

93600 90000 90100

1.54 1.58 2.15

60

1440

42

39000

97100

1.75

60

360

11

61800

32700

1.73

a

Conversion was determined using the 1H NMR spectrum. bMn and Mw/Mn were measured via gel permeation chromatography (GPC) using polystyrene as the standard. cMn,th = ([MMA]0/[CoIII-PVAc]0) × (MW of MMA) × conv + MWPVAc.

Figure 2. Reverse ATRP of MMA initiated by a PVAc macroinitiator (Mn = 8200 g/mol, Mw/Mn = 1.11) in benzene at 60 °C with the condition of [CoIII-PVAc]0/[CuBr2]0/[Bpy]0/[MMA]0/Cu(0) wire = 1/2/4.4/2000/1 cm, [MMA]0 = 4.0 M. (a) Plots of Mn and Mw/ Mn(PDI) versus conversion; (b) evolution of the GPC traces.

Figure 3. Reverse ATRP of MMA initiated by a PVAc macroinitiator (Mn = 10800 g/mol, Mw/Mn = 1.13) in benzene at 60 °C with the condition of [CoIII-PVAc]0/[CuBr2]0/[PMDETA]0/[MMA]0/Cu(0) wire = 1/2/2.2/2000/1 cm, [MMA]0 = 4.0 M. (a) Plots of Mn and Mw/Mn (PDI) versus conversion; (b) evolution of the GPC traces.

extension process generating PVAc-b-PMMA with an Mn equal to 105400 and an Mw/Mn ratio equal to 1.42 at 56% MMA conversion within 8 h (Table 1, entry 5). The molecular weight not only increased linearly with conversion but also matched the theoretical values (Figure 3). Considering the shift of GPC traces, the linearity of the kinetic plots, and the properly increasing molecular weight, the hybridized system using PMDETA as ATRP ligand appears to be as efficient as that using bpy. The reverse ATRP of MMA started from CoIII-PVAc (M n = 8700, M w /M n = 1.18), Cu(0) wire, and CuII(Me6TREN)Br2, which has an even higher KATRP value, showed a linear first-order kinetic plot up to 53% MMA conversion in 16 h. The polymeric product had the molecular weight of 74000 and a narrower molecular weight distribution,

as demonstrated by the Mw/Mn ratio of 1.35 (Table 1, entry 6). The linearly increasing molecular weight versus conversion associated with the relatively low and gradually declining polydispersity (Mw/Mn) demonstrated that the reverse ATRP of MMA was under control even though a moderate molecular weight deviation was observed (Figure 4). The obtained PVAcb-PMMA was a white powder, indicating the removal of most of the transition metal ions, which were further detected by ICP-AES as 1.36 ppm cobalt and 10.2 ppm copper (Figure 5). The functional groups of both PVAc and PMMA were identified in the 1H NMR spectrum (Figure 6). Compared to the results with bpy and PMDETA, the more smoothly shifted GPC traces with almost no tailing, and the narrowest molecular C


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Figure 6. 1H NMR spectrum for the poly(vinyl acetate)(8700)-bpoly(methyl methacrylate)(65300) block copolymer in CDCl3 (Table 1, entry 6).33

Chain Extension from CoIII-PVAc to PSty. This method of hybridizing CMRP and ATRP was further expanded to synthesize the block copolymer of PVAc-b-PSty because styrene has been widely used in the field of C/LRP but cannot be well controlled by the CMRP.16 The chain extension from CoIII-PVAc to PSty was first performed at 60 °C in benzene with the condition of [CoIII-PVAc]0/[CuBr2]0/[bpy]0/[Sty]0/ Cu(0) wire = 1/2/4.4/2000/1 cm and [Sty]0 = 4.0 M (Table 1, entry 8). The low reaction temperature of 60 °C was selected to avoid the self-initiation of styrene but may cause slow polymerization; thus, bpy, which enabled the most rapid chain extension of MMA, was used as the ATRP ligand. The formation of PVAc-b-PSty was a first-order kinetic process approaching 38% conversion in 3000 min. The polymeric product was characterized by GPC analysis, yielding Mn and Mw/Mn values of 86500 and 1.58, respectively, and by 1H NMR spectrum to confirm the coexistence of acetate and benzyl functional groups (Figure 7). The smoothly shifted GPC traces

Figure 4. Reverse ATRP of MMA initiated by a PVAc macroinitiator (Mn = 8700 g/mol, Mw/Mn = 1.18) in benzene at 60 °C with the condition of [CoIII-PVAc]0/[CuBr2]0/[Me6TREN]0/[MMA]0/Cu(0) wire = 1/2/2.2/2000/1 cm, [MMA]0 = 4.0 M. (a) Plots of Mn and Mw/Mn (PDI) versus conversion; (b) evolution of the GPC traces.

Figure 5. (a) Photograph of the poly(vinyl acetate)-b-poly(methyl methacrylate) block copolymer. This sample was measured by ICPAES and was found to have 1.36 ppm cobalt and 10.2 ppm copper. (b) Picture of the macroinitiator (CoIII-PVAc) dissolved in benzene, [CoIII-PVAc]0 = 2 × 10−3 M (514 ppm).

Figure 7. 1H NMR spectrum for the poly(vinyl acetate)(10900)-bpolystyrene(76500) block copolymer in CDCl3 (Table 1, entry 8).33

weight distribution suggested that ATRP with Me6TREN could better match the CMRP to generate the block copolymer of PVAc-b-PMMA. The chain extension from PVAc to PMMA using only CMRP was also performed as a control study and showed the characteristics of free radical polymerization (Table 1, entry 7, and Figure S8).

as well as the characteristics of ATRP, such as a linearly increasing molecular weight with conversion and gradually decreasing polydispersity, indicated a well-controlled polymerization process (Figures 8a,1 and 8b). The ATRP ligand effect has also been evaluated in the chain extension of polystyrene using PMDETA and Me6TREN under similar conditions (Table 1, entries 9 and 10). The styrene conversion approached D


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ATRP could not be fully understood via only thermodynamic considerations but should be further studied from the kinetic perspective. The measurement of kinetic parameters and theoretical calculation for the hybridized CMRP and ATRP are being processed. Block Copolymer Composition Confirmed by the Formation of Micelles. Micellization of block copolymers in solutions has been recognized as an effective method to demonstrate the formation of block copolymers and their controlled molecular weight distribution.53−55 Although both PVAc-b-PMMA and PVAc-b-PSty may not form micelles easily, poly(vinyl alcohol)-b-polystyrene (PVOH-b-PSty), derived from the hydrolysis of PVAc-b-PSty, is an amphiphilic block copolymer that could be used for micellization. PVAc-b-PSty was hydrolyzed according to the reported method,33 and the completion of the reaction was confirmed by the IR spectrum using the disappearance of the peak at 1735.62 cm−1 (−CO) and the occurrence of a signal at 3301.54 cm−1 (−OH) (Figure S13). The micelles formed in N-methyl-2-pyrrolidone (NMP) solution with 1% (w/w) PVOH-b-PSty were observed using TEM images (Figure 9). By using OsO4 as the staining agent,

Figure 8. (a) Plots of Mn and Mw/Mn (PDI) versus conversion for the reverse ATRP of Sty initiated by PVAc macroinitiator in benzene at 60 °C with the condition of [CoIII-PVAc]0/[CuBr2]0/[ligand]0/[Sty]0/ Cu(0) wire = 1/2/x/2000/1 cm, [Sty]0 = 4.0 M. The ligand was (1) bpy, x = 4.4; (2) PMDETA, x = 2.2; and (3) Me6TREN, x = 2.2. (b) Evolution of GPC traces for the reverse ATRP of Sty initiated by PVAc macroinitiator (Mn = 10900, Mw/Mn = 1.29) in benzene at 60 °C with the condition of [CoIII-PVAc]0/[CuBr2]0/[bpy]0/[Sty]0/ Cu(0) wire = 1/2/4.4/2000/1 cm, [Sty]0 = 4.0 M.

Figure 9. TEM images of micelles formed by PVOH-b-PSty 1% (w/w) in NMP solution.

approximately 40% within 2610 and 1440 min to generate PVAc-b-PSty with molecular weights of 48500 and 39000 for the systems with PMDETA and with Me6TREN, respectively. The molecular weight elevated properly with the conversion but deviated from ideality more significantly, and the values of polydispersity became higher (Figure 8a, 2 and 3), suggesting that a less efficient control process occurred when PMDETA and Me6TREN were used. The control study of styrene chain extension initiated by CoIII-PVAc under the condition of the CMRP only illustrated the properties of free radical polymerization, i.e., that high-molecular-weight polymers were formed at low monomer conversion rates within a relatively short time frame (Table 1, entry 11, and Figure S12). This result indicated that reverse ATRP with bpy effectively controlled the chain extension process, whereas reverse ATRP with PMDETA and Me6TREN showed only moderate control. Compared to the chain extension to PMMA and PSty, the slower polymerization showed better control of the molecular weight and molecular weight distribution, which matches the general concept of controlled/living radical polymerization.48 However, the ligand effect was reversed. The chain extension to polystyrene followed the reported trend of ATRP ligands that the ligand forming the copper complex with higher KATRP provides more rapid polymerization.50 Nevertheless, the slowest chain extension of PMMA was observed when Me6TREN was the ligand. The inconsistency of these two systems indicated that the mechanism of chain extension achieved by the CMRP and

the PVOH block appeared darker in the TEM images, where the PVOH core and PSty shell can be observed. The size distribution histogram of the micelles obtained by TEM measurements is shown in Figure S14, and the average diameter was ∼220 nm. The observed micellization confirmed that the hybridization of CMRP and ATRP can generate the block copolymer of PVAc-b-PSty.

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CONCLUSION The combination of CMRP and ATRP provided a new synthetic route, which is as simple as the regular reverse ATRP process and requires neither difunctional initiation nor chainend modification to prepare PVAc-b-PMMA and PVAc-b-PSty and perhaps other conjugated−unconjugated (active−inactive) block copolymers. The linearly increasing molecular weight with conversion and relatively narrow molecular weight distribution associated with smoothly shifted GPC traces demonstrated a well-controlled chain extension process for the propagation of the second block. Because the hybridization of CMRP and ATRP involved two types of transition metal species associated with the competition of several reaction pathways, the mechanism could be more complex than the simple combination of RT, DT, and ATRP. Further study of this hybridized process is in progress regarding the measurement of the kinetic parameters and theoretical calculations. This method can potentially expand the variety of block E


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thus, after the calculation, the block copolymer had 1.36 ppm cobalt and 10.2 ppm copper.

copolymers and contribute to studies of their morphology, physical property, and application.


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EXPERIMENTAL SECTION

ASSOCIATED CONTENT

S Supporting Information *

Materials. Methyl methacrylate (>99%, ACROS), styrene (>99%, ACROS), and vinyl acetate (>99%, ACROS) were purified by distillation under reduced pressure. Benzene (>99.7%, Aldrich) and tetrahydrofuran (>99%, MARCON) were purified by distillation with CaH 2 under nitrogen. Tris(2-(dimethylamino)ethyl)amine (Me6TREN) was synthesized by following the reported procedure.56 Cobalt(II) acetylacetonate (CoII (acac) 2 ), copper(II) bromide (CuBr2), copper wire (diameter 1.0 mm, ≥99.9%), 2,2′-bipyridine (bpy), and N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) were purchased from Sigma-Aldrich and used as received. Characterization. 1H NMR spectra were measured at 298 K using a mercury spectrometer (400 MHz) in CDCl3 (δ 7.24 ppm). Gel permeation chromatography (GPC) analysis for polymeric products was performed in THF at 30 °C at a flow rate of 1 mL min−1 using the Ultimate 3000 liquid chromatograph equipped with a 101 refractive index detector and styrene−divinylbenzene gel columns (Shodex KF802, KF-803 and KF-804). Polystyrene standards were used for the calibration. TEM images were obtained using a JEM-2100 instrument, and the micelles were observed by using an acceleration voltage of 200 kV. ICP-AES analysis was measured using an Agilent 725 instrument. Synthesis of PVAc Macroinitiator. CoII(acac)2 (0.0257 g, 1 × 10−1 mmol) and AIBN (0.0492 g, 3 × 10−1 mmol) were placed in a 50 mL Schlenk flask and then degassed by three vacuum/nitrogen cycles. Next, dry, degassed vinyl acetate (6.5 mL, 70 mmol) was added using a syringe under nitrogen. The orange mixture was stirred and heated to 60 °C to start the polymerization. The monomer conversion was followed by 1H NMR. After 4 h, the polymerization was stopped, and the residual monomer was removed by vacuum. The CoIII-PVAc macroinitiator was obtained after the purification including washing out the unreacted AIBN by ester and precipitating the CoII(acac)2 by benzene. General Procedure for Reverse ATRP of MMA (or Sty) Initiated by PVAc Macroinitiator. PVAc macroinitiator with Mn = 9800 g/mol and Mw/Mn = 1.19 (0.1505 g, 2 × 10−3 M), CuBr2 (0.0069 g), and copper wire (1 cm) were placed in a 50 mL Schlenk flask and degassed via three vacuum/nitrogen cycles. A solution of MMA (3.3 mL, 4.0 M), 2,2′-bipyridine (0.0106 g, 8.8 × 10−3 M), and benzene (4.4 mL) was degassed via three freeze−pump−thaw cycles and then transferred to the Schlenk flask with PVAc macroinitiator. Polymerization was initiated by heating the mixture to 60 °C. At the end of polymerization, the crude block copolymers were dissolved in THF and then purified by column chromatography using Al2O3 gel to remove the cobalt and copper complexes. Next, the solution was added to n-hexane to obtain the white precipitation as the product of block copolymers. Chain Extension from PVAc to PMMA (or PSty) by the CMRP Only. PVAc macroinitiator with Mn = 7900 g/mol and Mw/Mn = 1.06 (0.1625 g, 2 × 10−3 M) in a 50 mL Schlenk flask was degassed via three vacuum/nitrogen cycles, and a solution of MMA (2.9 mL, 4.0 M) and benzene (3.8 mL) that was degassed by three freeze−pump− thaw cycles was injected into the flask using a syringe. The chain extension was initiated by heating the solution to 60 °C. A similar procedure was applied to the chain extension of PSty. Hydrolysis of PVAc-b-PSty To Form PVOH-b-PSty. The block copolymer of PVAc-b-PSty (Mn = 86500 g/mol, Mw/Mn = 1.58) was dissolved in the mixed solution of THF and MeOH (THF/MeOH = 10 mL/15 mL) with the addition of KOH (0.02 g). The reaction was stirred at room temperature for 40 h. After the hydrolyzation, the PVOH-b-PSty product formed white precipitation in the solution, which was collected by filtration. IR spectroscopy was used to confirm the completion of hydrolysis. ICP-AES Analysis of PVAc-b-PMMA. The sample of 0.1 g of PVAc-b-PMMA (Mn = 60700 g/mol, Mw/Mn = 1.38) in 1 mL of THF was detected using ICP-AES. The result showed that the residual amount of cobalt and copper is 0.136 and 1.02 mg/L, respectively, and

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.5b01101. Representative GPC trace of CoIII-PVAc macroinitiator, experimental data of each polymerization, IR spectra of PVAc-b-PSty and PVOH-b-PSty block copolymer, and size distribution histogram of the PVOH-b-PSty micelles obtained from TEM images (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (J.-T.C). *E-mail: [email protected] (C.-H.P). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Ministry of Science and Technology, Taiwan (MOST 102-2113-M-007-007-MY2), for supporting this research.

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REFERENCES

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