Article pubs.acs.org/Macromolecules
Facile Arm-First Synthesis of Star Block Copolymers via ARGET ATRP with ppm Amounts of Catalyst Hangjun Ding,†,‡,¶ Sangwoo Park,†,¶ Mingjiang Zhong,†,⊥ Xiangcheng Pan,† Joanna Pietrasik,†,§ Christopher John Bettinger,*,‡,∥ and Krzysztof Matyjaszewski*,† †
Department of Chemistry, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, United States Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, United States § Institute of Polymer and Dye Technology, Lodz University of Technology, Stefanowskiego 12/16, 90-924 Lodz, Poland ∥ Department of Biomedical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, United States ‡
S Supporting Information *
ABSTRACT: Star polymers with block copolymer arms were prepared by atom transfer radical polymerization (ATRP) via an arm-first method. Several macroinitiators based on block copolymers (MIs), PBA-b-PtBA−Br, PtBA-b-PBA−Br, PSAN-b-PBA−Br, and PBA-b-PtBA−Br, were prepared by activators regenerated by electron transfer (ARGET) ATRP to maintain high chain-end functionality. Then the MIs were reacted with divinylbenzene as a cross-linker to form star-shaped polymers via ARGET ATRP. Several parameters including concentration of reducing agent, copper catalyst concentration, degree of polymerization (DP) of MIs, and composition of MIs were investigated. A high level of control was achieved by sequential feeding of the reducing agents for DPMI ≤ 100. Stars in >95% yield and with narrow molecular weight distributions (Mw/Mn < 1.3) were obtained under the optimized polymerization condition.
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INTRODUCTION The development of reversible deactivation radical polymerization (RDRP), also termed controlled radical polymerization (CRP), provided procedures for the facile synthesis of welldefined polymers with complex architectures and predetermined chemical compositions.1,2 One class of these materials, receiving increased attention, are star block copolymers which contain multiple linear block copolymer arms connected to a central core.3−5 Star block copolymers have many unique properties because the star molecules combine special features of both, block copolymers with tunable block composition and lengths, and star polymers, with compact structure, globular shape, and multifunctionality, into one entity.6−10 Compared to other core−shell nanoscale materials, star block copolymers are readily accessible and can find potential applications as engine oil additives, coatings, lithographic or biomedical devices and as unimolecular containers for nanomaterials.11−19 Atom transfer radical polymerization (ATRP)2,20−22 is one of the most robust RDRP methods and typically allows synthesis of star block polymers via three different strategies: “core-first”, “coupling-onto”, and “arm-first” (Scheme 1).23 The “core-first” method for star polymers exploits a procedure for polymerization of monomers from multifunctional initiators (core) to grow arms from the core.24,25 The retention of living character of the initiating sites at the © XXXX American Chemical Society
periphery of each arm can be further used for chain extension with second monomers to form star block copolymers. The number of arms per star polymer can be predetermined by the number of initiating groups on the core. However, additional and sometimes tedious reaction steps are required for the synthesis of well-defined multifunctional (star) cores.26,27 In the “coupling-onto” approach, α- or ω-functional polymers (arms) are specifically combined with a multifunctional agent (core) by highly efficient complementary coupling reactions, such as click reactions.28,29 Because of the low concentration of the chainend groups on the (co)polymers and steric congestion at the reactive sites, highly efficient coupling reactions are required to achieve pure uniform star polymers in high yields.30,31 The third technique“arm-first”can be typically divided into two approachesmacroinitiator (MI) and macromonomer (MM) methods. In both procedures, the macromolecules (either MI or MM) can be incorporated into the formed core of the star by copolymerization with di- or multivinyl compounds.32−34 Star polymers formed by the MI method can be utilized by chain extension from MI with cross-linkable monomers such as divinyl monomers. The MIs will be then Received: July 23, 2016 Revised: August 29, 2016
A
DOI: 10.1021/acs.macromol.6b01597 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Scheme 1. Three Approaches for Block Star Polymer Synthesis
ATRP.41 Another approach employed electrochemically mediated ATRP,45 also successfully applied to the synthesis of star polymers.46 Herein, we reported a facile methodology for preparation of uniform star block copolymers in high purity and high yields by an arm-first method via ARGET ATRP.
converted to arms of the star molecules and divinyl compounds can form a densely cross-linked core.35−37 On the other hand, star molecules formed by MM method can also be prepared by reaction with (low molar mass) initiators and multifunctional cross-linking agents to bind a core.38−40 These “arm first” approaches have several advantages in synthesis of star polymers with multiple arms over the core-first or couplingonto procedures. Arm-first approaches allow for easily tuned arm composition by using predesigned MIs such as block, gradient, or random MIs. Nevertheless selection of a suitable CRP method is crucial to obtain well-defined star block copolymers in a facile manner. For example, star synthesis by normal ATRP generally used relatively high concentrations of copper based catalyst, which required extensive purification of the product to remove the catalyst complex.34 A further limitation was the relatively high amount of radical−radical termination reactions resulting in a low conversion of MIs and broad molecular weight distribution of the star polymers as a consequence of star−star coupling reactions.37 ATRP systems with low ppm catalysts loading were developed to resolve these limitations and exploited for star polymer synthesis.41 Among these procedures, activators regenerated by electron transfer (ARGET) ATRP utilizes a reducing agent for spontaneous (re)generation of the activator (Cu I/L) from formed deactivator (X−CuII/L).42−44 Combining ARGET ATRP and slow feeding of the reducing agent system can allow controlling the concentration of active radicals in the ATRP reaction mixture and thus provide uniform star copolymers in a relatively short reaction time when compared to normal
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EXPERIMENTAL SECTION
Materials. n-Butyl acrylate (BA, 99%), tert-butyl acrylate (tBA, 99%), styrene (St), acrylonitrile (AN), and divinylbenzene (DVB, 80%) were purchased from Aldrich and purified by passing through a column filled with basic alumina. Anisole (Aldrich, 99%), CuBr2 (Acros, 99%), ethyl 2-bromoisobutyrate (EBiB, Acros, 98%), tin(II) 2-ethylhexanoate (SnII(EH)2, Aldrich, 95%), DMF (Aldrich, 99%), were used as received. Tris(2-pyridylmethyl)amine (TPMA) was synthesized according to the previously reported procedure.47 Synthesis of PBA−Br Macroinitiator Using ARGET ATRP. General Conditions. The initial molar ratio of reagents were [BA]0/ [EBiB]0/[SnII(EH)2]0/[CuBr2]0/[TPMA]0 = 67/1/0.05/0.0033/0.05 ([BA]0 = 0.2 M). CuBr2 (7.8 mg, 50 ppm), TPMA (150.0 mg) and 50 mL of anisole were added to a 200 mL Schlenk flask. The flask was subjected to sonication, and then DMF (5.0 mL) was added to the flask to provide a 1H nuclear magnetic resonance (NMR) internal standard. The mixture was bubbled with nitrogen (N2) for 30 min to remove O2. BA was purified by passing it through a basic alumina column to remove inhibitor and then bubbled with N2 for 30 min. Then 50 mL of BA was transferred to the reaction flask by syringe under protection of N2. The initiator, EBiB, 2.02 mL, was added to the flask. A mixture of SnII(EH)2 (0.27 mL) and anisole (10 mL) was deoxygenated by bubbling with N2 for 5−10 min, and 1 mL of the mixture was added to the reaction flask under protection of N2 to reduce part of the CuII catalyst complex and initiate the polymerization. The flask was sealed with a glass stopper and immersed in an B
DOI: 10.1021/acs.macromol.6b01597 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Scheme 2. Synthetic Procedure for PBA-b-PtBA Star Block Copolymer
oil bath set at 70 °C. At timed intervals, samples were withdrawn and diluted with THF for GPC (with PMMA calibration) and with CDCl3 for NMR analysis. The reaction was stopped after 3h and was quenched by adding an excess amount of oxygenated THF. The resulting polymers were purified by passing the solution through a neutral alumina column to remove the catalyst followed by rotary evaporation to remove the solvent and the residue was dried under vacuum at room temperature. A similar procedure was used to synthesize the PtBA macroinitiator. Synthesis of PBA-b-PtBA−Br Diblock Copolymer from PBA− Br MI. General Conditions. The initial molar ratio of the reagents were [tBA]0/[PBA−Br]0/[Sn(EH)2]0/[CuBr2]0/[TPMA]0 = 30/1/ 0.05/0.01/0.25. A clean dry Schlenk flask was charged with CuBr2 (3.7 mg, 50 ppm), TPMA (12.2 mg), and a solution of the PBA−Br macroinitiator (1.0 g) in anisole (10 mL). The flask was sonicated, and then DMF (1.0 mL) was added to provide an internal NMR standard. tert-Butyl acrylate (tBA) was purified by passing it through a basic alumina column to remove inhibitor and then bubbling with N2 for 30 min. Five mL of the deoxygenated tBA was then added to the reaction flask. A solution of SnII(EH)2 (0.3 mL) in degassed anisole (10 mL) was deoxygenated by bubbling with N2 for 5−10 min, and a 1 mL aliquot of the solution was added to the reaction flask. The flask was sealed with a glass stopper and immersed in an oil bath set at 70 °C. At timed intervals, samples were withdrawn and diluted with THF for GPC analysis (with PMMA calibration) and with CDCl3 for NMR analysis. The reaction was stopped after 4h by adding an excess amount of THF to quench the reaction. The resulting solution was purified by passing through a neutral alumina column to remove the catalyst and the solvent removed by rotary evaporation then the remaining polymer was dried under vacuum at room temperature. Similarly, a PtBA-b-PBA−Br diblock copolymer was also prepared by ARGET ATRP. Synthesis of PBA-b-PtBA Star Copolymer Using ARGET ATRP. PBA-b-PtBA−Br diblock copolymers were used as MIs for the synthesis of block star copolymers. An ARGET ATRP reaction was carried out using SnII(EH)2 as reducing agent, CuBr2/TPMA as catalyst, and divinylbenzene (DVB) as a cross-linker. General conditions: the initial molar ratio of reagents were [MI]/[DVB]/ [SnII(EH)2]/[CuBr2]/[TPMA] = 1/14/0.2/0.01/0.1. CuBr2 (0.9 mg), and TPMA (12.1 mg) were added to a clean and dry Schlenk flask. Then a solution of the PtBA-b-PBA−Br MI (5.0 g) dissolved in 2 mL anisole after bubbling with N2 for 60 min was added. DVB was passed through a column of basic alumina, and 0.8 mL of it was injected to the flask. The flask was sealed with a glass stopper and immersed in an oil bath set at 110 °C. A solution of SnII(EH)2 (2.7 mL) in degassed anisole (10 mL) was deoxygenated by bubbling with N2 for 5−10 min, and 0.1 mL of the solution was added to the reaction flask at the different timed intervals0, 5, 10, 20, 40, and 50 h. At timed intervals, samples were withdrawn and diluted with THF for GPC analysis and
with CDCl3 for NMR analysis. The reaction was stopped after 55 h by adding an excess amount of THF to quench the reaction. The resulting polymer solution was purified by passing it through a neutral alumina column to remove the catalyst. The solids were precipitated by addition of the solution to cold methanol, and the solid polymer was obtained after evaporation of residual solvent. The samples were dried under reduced pressure at room temperature. A similar method was used to synthesize the PtBA-b-PBA star. Synthesis of PSAN−Br MI Using ARGET ATRP. General Conditions. The molar ratio of reagents were [St/AN]0/[EBiB]0/ [SnII(EH)2]0/[CuBr2]0/[TPMA]0 = [50/30]/1/0.01/0.04/0.2. A clean dry Schlenk flask was charged with CuBr2 (2.9 mg, 30 ppm), TPMA (75.3 mg), and anisole (10 mL). Styrene (St) and acrylonitrile (AN) were purified by passing through a basic alumina column to remove inhibitor and then bubbling with N2 for 30 min. Then 30 mL of St and 10 mL of AN was added to the flask, and EBiB was quickly added into the flask. A stock solution of the reducing agent was prepared by adding SnII(EH)2 (0.8 mL) to degassed anisole (10 mL) and deoxygenated by bubbling with N2 for 5−10 min, and 1 mL of the solution was added to the reaction flask. The flask was sealed with a glass stopper and immersed in 70 °C oil bath. At timed intervals, samples were withdrawn and diluted with THF for GPC analysis (with PS calibration) or diluted with CDCl3 for NMR analysis. The reaction was stopped after 18 h and passed through neutral alumina to remove the copper catalyst. The polymer solution was added to methanol to precipitate the poly(styrene-co-acrylonitrile) (PSAN) macroinitiator. The white powder was dried under vacuum. Synthesis of PSAN-b-PtBA−Br Using ARGET ATRP. General Conditions. The molar ratio of reagents was [tBA]0/[PSAN]0/ [SnII(EH)2]0/[CuBr2]0/[TPMA]0 = 120/1/0.01/0.06/0.3. A clean dry Schlenk flask was charged with the initiator of PSAN−Br (1 g), CuBr2 (2.1 mg, 500 ppm), TPMA (13.6 mg), and anisole (5 mL). The mixture was stirring to form a homogeneous solution and then bubbled with N2 for 60 min. tBA was purified by passing through a basic alumina column to remove inhibitor and then bubbled with N2 for 30 min. Then 3 mL of tBA was added into the above flask. SnII(EH)2 (0.5 mL) was added into degassed anisole (10 mL) to prepare a stock solution which was deoxygenated by bubbling N2 for 5−10 min, and a 0.1 mL solution was added to the reaction flask to activate the catalyst. The flask was sealed with a glass stopper and immersed in 70 °C bath. At timed intervals, samples were withdrawn and diluted with THF for GPC (with PS calibration) and with CDCl3 for NMR analysis. The reaction was stopped after 40 h, and copper was removed by passing the solution through a neutral alumina column. The product was precipitated by adding the solution to methanol/H2O (9/1). The white sticky powder was collected and dried under vacuum. Synthesis of PSAN-b-PtBA Star Using ARGET ATRP. General Conditions. The initial molar ratio of reagents was [MI]0/[DVB]0/ C
DOI: 10.1021/acs.macromol.6b01597 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Table 1. Synthesis of PBA and PtBA MIs using ARGET ATRP entry
monomer
DPa
SnII(EH)2b
Cu (ppm)c
time (h)
convn (%)d
Mn,gpce
Mw/Mne
1 2 3 4 5
BA BA BA tBA tBA
30 30 67 30 30
0.01 0.01 0.05 0.05 0.01
100 500 50 75 250
3 20 3 1 7
55 60 43 70 48
1600 2500 6100 6800 2500
1.32 1.11 1.29 1.96 1.25
a
Target DP. b[SnII(EH)2]/[EBiB]. cVersus monomer mole concentration. dDetermined by NMR. eDetermined by THF GPC with PMMA calibration.
[SnII(EH)2]0/[CuBr2]0/[TPMA]0 = 1/14/0.2/0.01/0.1. CuBr2 (0.09 mg), and TPMA (1.12 mg). were added to a clean dry Schlenk flask. The PSAN40-b-PtBA24−Br (0.25 g) macroinitiator was dissolved in 2 mL of anisole and placed in the flask, and the mixture was bubbled with N2 for 60 min. DVB was passed through a column on basic alumina, and 0.08 mL of the DVB was added to the flask. SnII(EH)2 (0.25 mL) was mixed with degassed anisole (10 mL), additional N2 bubbling was carried out for 5−10 min, and 0.1 mL of the solution was added to the reaction flask at the different timed intervals0, 5, 10, 20, 40, and 50 h. The flask was sealed with a glass stopper and immersed in 90 °C oil bath. At timed intervals, samples were withdrawn and diluted with THF for GPC (with PS calibration). The reaction was stopped, and copper catalyst was removed by passing the mixture through a column of neutral alumina. The product was obtained by adding the solution to methanol to precipitate the solids which were dried under vacuum. Characterization. Monomer conversions were determined by nuclear magnetic resonance (NMR, Bruker Avance 300 MHz) or gas chromatography (GC) using Shimadzu GC-14A equipped with a capillary column (DBWax, 30 m × 0.54 mm × 0.5 μm, J&W Scientific). The polymer samples were separated by gel permeation chromatography (GPC) with Polymer Standards Services (PSS) columns (guard, 105, 103, and 102 Å) with THF eluent at 35 °C, flow rate = 1.00 mL/min and differential refractive index (RI) detector (Waters 2410). The apparent molecular weights and molecular weight distributions (MWD or Mw/Mn) were determined with a calibration based on linear polystyrene (PSt) or poly(methyl methacrylate) (PMMA) standards using WinGPC 7.0 software (PSS). Eluogram area fractions of both star and linear polymers were determined by multipeak splitting of the eluogram of GPC results. The absolute molecular weights (Mw,MALLS) were determined using ASTRA software from Wyatt Technology from a multiangle laser light scattering (MALLS) detector (Wyatt Technology, DAWN EOS) equipped with THF GPC.
small amount of SnII(EH)2, for instance, Table 1, entries 1 and 2 showed narrow MWD (95%) were achieved. The star yield increased when the DP of MI decreased. PtBA-b-PBA MIs were also prepared and used for star synthesis. MIs with two different DPs were prepared: DPtotal = 80 and 100, Table 2, entries 6 and 7. The results showed high chain-end functionality, resulting in good star yield when using MI with DP ≤ 100. Typically, Narms were higher than 30, when using DP MI ≤ 100, indicating large number of arms incorporated to the core under the optimal reaction conditions. These two examples showed that different compositions of BA/ tBA did not affect yields in star synthesis; however using PBA as the second block in MI significantly resulted in more number of arms of synthesized stars (Narm = 75, 80 vs 45, 50; entry 6, 7 vs entry 1, 2; Table 2). This observation could be attributed to a lower steric hindrance of BA compared to tBA.
Figure 3. Influence of DP of MIs on the formation of star polymers. GPC traces of star synthesis using MI = (a) PBA50-b-PtBA30, (b) PBA80-b-PtBA20, (c) PBA20-b-PtBA100, (d) PBA50-b-PtBA100, (e) PBA50-b-PtBA300, (f) PtBA30-b-PtBA50, and (g) PtBA20-b-PtBA80. Apparent MW was obtained from the linear PMMA standards curve.
Synthesis of Poly(styrene-co-acrylonitrle) (PSAN)-bPtBA Star Block Copolymers. Random copolymers of St and AN (styrene-co-acrylonitrile, SAN) are commercially important thermoplastics with unique properties, such as excellent chemical resistance, dimensional stability, impact strength and ease of processing. A styrene (St) and acrylonitrile (AN) copolymer was incorporated as the outer segment of a MI for formation of block star copolymers and their synthesis was systemically investigated by ARGET ATRP. PSAN-PtBA-stars could be dispersed in PMMA matrices, due to favorable between both polymers.50 A series of PSAN was synthesized by ARGET ATRP to optimize reaction conditions and prepare well-defined MIs. Parts a−c of Figure 4 show the results of ARGET ATRP of PSAN with the ratio of St/AN = 50/30. The initial ratio of reagents were [St/AN]0/[EBiB]0/[SnII(EH)2]0/[CuBr2]0/ F
DOI: 10.1021/acs.macromol.6b01597 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules
Star block copolymers with different DP of PSAN-b-PtBA MI were prepared by normal ATRP and ARGET ATRP, Figure 5.
Figure 4. (a) GPC traces of St/AN polymerization; (b) first-order kinetic plot and conversion of St/AN; (c) MW and MWD versus monomer conversion determined by THF GPC with PSt calibration; (d) GPC trace of chain extension of tBA from PSAN MI; (e) firstorder kinetic plot and conversion of tBA; (f) MW and MWD versus monomer conversion determined by THF GPC with linear PSt calibration.
[TPMA]0 = [50/30]/1/0.01/0.04/0.2 at 70 °C in anisole. Since the copolymerization was carried out under azeotropic d[M ]
conditions, ( d[M St ] = AN
[MSt] [MAN]
=
1 − rAN , 1 − rSt
Figure 5. GPC traces during the synthesis of PSAN-b-PtBA star copolymer of (a) PSAN40-b-PtBA24 (normal ATRP), (b) PSAN40-bPtBA24 (ARGET ATRP), (c) PSAN70-b-PtBA40, (d) PSAN70-b-PtBA70, and (e) PSAN70-b-PtBA90. Apparent MW was measured by THF GPC with linear PSt calibration.
where [M] is monomer
concentration, rx is reactivity ratio of x monomer [rSt = 0.4 and rAN = 0.04]),51,52 and linear first-order kinetic plots were obtained for both monomers (Figure 4) with similar conversions. GPC analysis showed linear increase of MW versus total monomer conversion, matching well with theoretical MW values, and decreasing MWD with increasing monomer conversion, Mn = 3500, Mw/Mn = 1.09, and DPSAN = 40. Similarly a PSAN with DP = 70 (Mn = 6000, Mw/Mn = 1.07, and DPSAN = 70) was synthesized under similar conditions with the initial ratio of reagents: [St/AN]0/[EBiB]0/[SnII(EH)2]0/ [CuBr2]0/[TPMA]0 = [100/60]/1/0.01/0.08/0.4 at 70 °C in anisole (Figure S2). The PSAN70 was also used for MI for chain extension with tBA as well as for star copolymer synthesis. Using two different PSAN MIs (DPSAN = 40 or 70), chain extension with tBA was also carried out using ARGET ATRP and different target DP ([M]0/[MI]0) for the second segment. Parts d and e of Figure 4 showed the results of the chain extension from PSAN40. Block copolymers were successful (PSAN40-b-PtBA24), GPC analysis indicated clean peak shift from low to higher molar mass region. The obtained PSAN-bPtBA MI showed Mn = 7000 and Mw/Mn = 1.10. Similarly three more block MIs were prepared from PSAN70PSAN70-bPtBA40 (Mn = 10000 and Mw/Mn = 1.10), PSAN70-b-PtBA70 (Mn = 14000 and Mw/Mn = 1.15), and PSAN70-b-PtBA90 (Mn = 17000 and Mw/Mn = 1.30) (Figure S2).
When the polymerization was carried out by normal ATRP with PSAN40-b-PtBA24 MI, overall yield of the star copolymer was 85%, determined from eluogram. Approximately 15% MIs remained the reaction mixture after 40 h, and no further peak shift was observed. The residual MIs might indicate some loss of chain-end functionality by the uncontrolled initial intermolecular cross-linking reaction, Figure 5a. Furthermore, some star−star coupling was also observed, Figure 5a, arrow. This can be attributed to a high amount of activator which could probably still be present at the end of polymerization stage, and CuI/L could activate halides within the star polymers so that intermolecular cross-linking reaction between star−star molecules could occur. In contrast, ARGET ATRP with reducing agent feeding system showed improvement of star yield and narrower MWD than under previous stars synthesis conditions via normal ATRP, by minimizing initial intermolecular coupling reactions. In addition, no star−star coupling products were observed. Presumably, activators would predominantly react with MIs rather than with terminal star−Br due to higher diffusivity of smaller molecules (MIs) and [CuI/ L]. Therefore, no gelation was observed under optimal polymerization conditions. Under such conditions for PSANPtBA-star copolymers, a total 0.2 eq. of reducing agents were G
DOI: 10.1021/acs.macromol.6b01597 Macromolecules XXXX, XXX, XXX−XXX
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sequentially injected to the reaction mixture: 0.01, 0.03, 0.06, and 0.1 equiv was added at 0, 1, 2.5, and 5 h, respectively. The effect of total DP of the MIs on the star synthesis was also evaluated. When high MIs with DPs were used (DPMI ≥ 140), a dramatic decrease in star yield was observed while over 90% of MIs were incorporated into stars when DPMIs ≤ 110 by area fraction of eluogram (Figure S3).
CONCLUSIONS The star block copolymers were synthesized by ARGET ATRP with the “arm-first” MI method. Several parameters such as normal/ARGET ATRP, degree of polymerization of MI, monomer sequence, and different monomer compositions were examined. A high level of control was achieved by sequential feeding of the reducing agent and for DPMI ≤ 110. Under the optimal condition, > 95% of star yield was achieved. ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b01597. Details of multiple peak separation of star/MI from eluogram using PSAN-b-PtBA and PBA-b-PtBA as MIs with different DP and GPC traces during polymerization of SAN and chain extension from PSAN MIs with tBA, synthesis data for PSAN-b-PtBA star polymers, and an AFM image of the film composed of SAN70-b-AA40-star block copolymers(PDF)
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REFERENCES
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AUTHOR INFORMATION
Corresponding Authors
*(C.J.B.) E-mail:
[email protected]. *(K.M.) E-mail:
[email protected];. Present Address ⊥
Department of Chemical and Environmental Engineering, Yale University, 17 Hillhouse Ave, New Haven, CT 06511 Author Contributions ¶
H.D. and S.P. contributed equally. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Financial support from Natural Science Foundation (DMR 1501324), Natural Science Foundation of China (NSFC51273022), and National Science Centre, Poland (via Grant UMO-2014/14/A/ST5/00204) is acknowledged.
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ABBREVIATIONS PtBA, poly(tert-butyl acrylate); PBA, poly(n-butyl acrylate); PSAN, poly(styrene-co-acrylonitrile); ATRP, atom transfer radical polymerization; ARGET, activator regenerated by electron transfer, ATRP; DP, degree of polymerization; RDRP, reversible deactivation radical polymerization; CRP, controlled radical polymerization; MI, macroinitiator; MM, macromonomer; MALLS, multiangle laser light scattering H
DOI: 10.1021/acs.macromol.6b01597 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
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DOI: 10.1021/acs.macromol.6b01597 Macromolecules XXXX, XXX, XXX−XXX
