Statistically Syndioselective Coordination (Co)polymerization of 4

Article pubs.acs.org/Macromolecules

Statistically Syndioselective Coordination (Co)polymerization of 4‑Methylthiostyrene Zichuan Wang,†,‡ Dongtao Liu,† and Dongmei Cui*,† †

State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China ‡ Graduate School of the Chinese Academy of Sciences, Beijing 100039, China S Supporting Information *

ABSTRACT: The homopolymerization of a polar monomer, 4-methylthiostyrene (MTS), was successfully achieved by a rare-earth metal based catalyst in the highest activity of 45.1 × 104 g molY−1 h−1 and the excellent syndioselectivity (rrrr > 99%). The polymerization was rather controllable that the resultant poly(methylthiostyrene)s (PMTS) had molecular weights comparable to the theoretic ones reaching up to 1.7 × 105 while the molecular weight distributions were narrow (PDI = 1.3−1.9). Moreover, the copolymerization of this polar MTS with the nonpolar styrene (St) performed fluently under various MTS-to-St ratios in a quasi-living mode. The monomer reactivity ratios were rMTS = 1.08 and rSt = 0.77, following the first Markov statistics, and was close to the ideal random copolymerization. Therefore, a series of unprecedented statistical random copolymers, P(St-r-MTS)s, where the compositions were strictly closed to the monomer fed ratios, had been accessed. Strikingly, both monomer sequences remained highly syndiotactic as their homopolymers regardless of the compositions, thus endowing P(St-r-MTS)s variable glass transition temperatures and melting points. The shortest number-averaged sequence length for these copolymers P(St-r-MTS) crystallizing from the melts was n̅St = 5.75 for PS sequences and nM ̅ TS = 8.11 for PMTS.

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INTRODUCTION Introducing functional groups in syndiotactic polystyrene (sPS) is a promising method to improve its surface property, adhesive property, affinity for dyes, and compatibility with other polar polymers.1 Postmodification such as sulfonation,2 acetylation,3 benzoylation,4 borylation,5 or hydrogenation6 is a convenient method to surface functionalization of sPS without changing the bulk properties of sPS.7 Comparatively, the copolymerization of styrene with functionalized styrenes is a more convenient and controllable manner with respect to the number and position of the polar groups substituted on the macromolecular chains.1,8 However, homo- and copolymerizations of functionalized olefins including styrene derivatives have been a long-standing academic research challenge in polymer science because the commonly employed catalysts in these polymerizations are based on the Lewis acid group 3 or 4 transition metals that are extremely sensitive to these functional groups owing to the Lewis acid−base interaction.9 Therefore, loss of activity and selectivity, low polar monomer insertion, and low molecular weight are always encountered problems. Styrenic monomers bearing meta- and para-halogen substituents10 are hardly polymerized by the half-titanocene CpTiCl3/ MAO, although it is highly active to the alkyl-substituted styrenes.10,11 p-Dimethylaminostyrene has been reported to be polymerized by the half-titanocenes Cp*TiMe3/B(C6F5)3 and Cp*Ti(TEA)/MMAO and the half-scandocene Cp′Sc© XXXX American Chemical Society

(CH2C6H4NMe2-o)2/[Ph3C][B(C6F5)4] in high activity and distinguished syndioselectivity, whereas affords low molecular weight or insoluble products with broad molecular weight distributions.12 Therefore, masking the polar atoms by bulky groups such as trialkylsilyl13 and borane,14 complexing with metal alkyls (the activators), or separating them with a long spacer apart from the olefinic locus of the insertion15 is requisite, which, however, still arouses dramatic drops of the activity and the selectivity. Very recently, our group reported the syndioselective and isoselective polymerizations of methoxystyrenes with remarkable activities and high molecular weights by using the constrained-geometry-configuration rareearth metal complex (Flu-CH2-Py)Y-(CH2SiMe3)2(THF)2 and the β-diketiminatoyttrium and lutetium based precursors.16 To date, the copolymerization of heteroatomic substituted styrenes and St has been less reported; therefore, the fairly controlled insertion of the substituted styrene units and their distribution along the macromolecular chains owing to the big difference in the reactivity ratios for the polar and nonpolar monomers, in particular, retention of the stereoregularity, have still remained challenging and unexplored. Received: October 14, 2015 Revised: January 7, 2016

A

DOI: 10.1021/acs.macromol.5b02263 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 1. Homopolymerizations of St and MTS by Using 1/[Ph3C][B(C6F5)4]/[AliBu3]a entry

monomer

[M]/[Y]

time (h)

conv (%)

activityb

Mnc (×104)

PDIc

Tgd (°C)

Tmd (°C)

1 2 3 4 5 6 7 8 9e

St MTS MTS MTS MTS MTS MTS MTS MTS

500 250 500 750 1000 500 750 1000 500

10 min 2 2 2 2 6 12 48 6

99 93 77 56 60 95 58 63 87

310.1 17.5 28.9 31.6 45.1 11.9 5.4 2.0 10.9

14.7 5.7 10.4 14.0 16.1 13.4 14.8 17.0 11.6

1.3 1.7 1.9 2.0 1.8 1.8 1.9 1.9 1.8

99 103 104 107 106 103 106 104 108

260/270 254/259 256/263 252/255/263 253/258 252/258 254/262 252/257 253/258

General polymerization conditions: complex 1 (10 μmol), [Y]/[Ph3C][B(C6F5)4]/[AliBu3] = 1/1/10 (mol/mol/mol), toluene (5 mL), Tp = 25 °C, unless otherwise noted. bGiven in 104 g molY−1 h−1. cDetermined by GPC in 1,2,4-trichlorobenzene at 150 °C against polystyrene standard. d Determined by DSC. e2 mL of toluene as the solvent. a

Table 2. NBO Analysis of the Charge for Each Carbon in Styrene and MTS

carbon

a

b

c

d

e

f

sum

MTS(1)

−0.360

−0.189

−0.099

−1.598

−0.351

−0.190

−0.083

−0.237 −0.210 −0.199 −0.196

−0.179

St(2)

−0.161 −0.163 −0.181 −0.179

−0.201

−1.580

methylamino group as well as its weak electron donating property (its NBO values are close to those of St; Table 2 and Figure S1). Whereas, further increasing the MST concentration did not arouse the corresponding increase of the conversion for a long polymerization time (Table 1, entries 7−9) because the active metal−PMTS species precipitated from the polymerization solution, and the aggregation of methylthio groups (except those coordinating ones) around the active metal centers became more serious to inhibit the coordination of reactive CC bonds.19 This meant the polar groups indeed affected the polymerization behavior no matter how weak they were, since the same catalytic system we reported previously exhibited an extremely high activity for the polymerization of St.18 Delightedly, the resultant polymers have high molecular weights with moderate molecular weight distributions, displaying a certain degree of controlled polymerization mode. More remarkably, the obtained polymers possess excellent syndiotacticity (rrrr > 99%), which can be confirmed by the typical triplet−quintet resonances arising from the methylene CH2 and methine CH protons in the 1H NMR spectrum, and the sharp singlet resonances of ipso carbon at 142.18 ppm and CH2 at 44.34 ppm and CH at 40.62 ppm in the 13C NMR spectrum (Figure 1). The differential scanning calorimetry (DSC) curves showed that PMTS display higher glass transition temperatures around 106 °C but lower melting points within 252−263 °C as compared to those of sPS, indicating that they may have the similar complex polymorphism. Copolymerization of MTS and St. Intrigued by the distinguished polymerization behavior of MST, the copolymerization of MTS with St was carried out with the same catalytic system at different MST-to-St monomer molar ratios

Among the variety of functional group, sulfide species has a relatively weaker polarity, which is less poisonous to catalyst and readily reduced to sulfhydryl group, a convenient building block for further modification. Herein, we wish to report the highly active homopolymerization of methylthio-substituted styrene (MTS) with Hammett constant (σp = 0) equal to St17 and its copolymerization with St using the yttrium complex (Flu-CH2-Py)Y-(CH2SiMe3)2(THF)2 as the precursor18 to give, unprecedentedly, the statistical random copolymers having excellent syndiotacticity, variable MTS insertion rates, Tg, and Tm. The kinetics, the polymerization mode, the dynamic chain length, and its correlation with the physical properties will also be provided.

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RESULTS AND DISCUSSION Homopolymerization of MTS. The polymerization of methylthio-substituted styrene (MST) was performed by using the yttrium precursor (Flu-CH2-Py)Y−(CH2SiMe3)2(THF) (1) activated by [Ph3C][B(C6F5)4] and AliBu3 at room temperature under various monomer-to-catalyst molar ratios (MST/Y = 250−1000/1) (Table 1). The polymerization reached a high conversion (93%) at the ratio of 250:1 in 2 h (Table 1, entry 2), and an even higher conversion of 95% was obtained by increasing the MST loading to 500 equiv, albeit at a prolonged polymerization time (6 h) (Table 1, entries 3 and 6). This result represented a rare example that the coordination homopolymerization of a polar monomer can be carried out at high monomer loadings, leading to a catalytic activity of 4.5 × 104 g molY−1 h−1 that is competitive to the recorded highest value for the homopolymerization of polar styrenic monomers.16b This might be attributed to the weak coordination ability of the methylthio group to the active metal centers as compared to many other polar groups such as methoxyl or B

DOI: 10.1021/acs.macromol.5b02263 Macromolecules XXXX, XXX, XXX−XXX

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This stimulated us to explore further the copolymerization kinetics as well as the microstructure and the sequence distribution of the product. To this end, following the conditions shown in Table 2, entries 2−7, the copolymerizations were designed and terminated at low conversions ( 99%) within 48 h (Table 3, entry 10), which was impossible for the homopolymerization of MST (Table 1, entry 8). Nevertheless, in all cases, the molar fraction of MST in the copolymer, FMTS, was in well agreement with the fed fMTS; the obtained polymers had molecular weights closing to the theoretic ones and narrow molecular weight distributions, which were able to dissolve in dimethylbenzene (130 °C), tetrahydrofuran, chloroform and ethyl ether. These results were drastically contrary to many copolymerizations involving a polar monomer that allow usually low polar monomer loading to give copolymers with low molecular weights and limited polar monomer insertions.

Figure 2. Fineman and Ross plot for the copolymerization of MTS and styrene and least-squares best fit line.

homopolymerization, and was more easily incorporated into the macromolecular chains than St. The product of reactivity ratios rMTS × rSt being 0.83 suggested a roughly ideal copolymerization, which could explain well the above results that the composition of the copolymers were close to those of monomer loadings. However, it was contrary to many previously reported copolymerizations involving polar olefins and olefins, where r1 (polar olefin) and r2 (olefin) were quite different to provide copolymers with low molecular weights and low polar monomer insertion and/or blocky structure, since the continuous insertion of polar monomer units and insertion of a none polar monomer after the polar units are impossible.13a The copolymerization results were also strikingly contrast to the homopolymerization behaviors of both monomers. As mentioned above, the competitive coordination between

Table 3. Copolymerization of MTS with Styrenea

entry

f MTSb (mol %)

time (h)

yield (%)

FMTSc (mol %)

Mnd (×104)

PDId

Tge (°C)

Tme (°C)

1 2 3 4 5 6 7 8 9 10g

10 20 30 40 50 60 71 80 89 93

1 4 8 8 8 8 8 8 8 48

99 91 94 97 95 95 90 94 86 >99

11 21 30 38 49 57 67 73 84 93

13.0 11.1 16.8 19.1 18.5 19.3 16.2 16.3 20.0 29.4

1.9 1.4 1.7 1.4 1.8 1.7 2.0 1.9 1.7 1.9

96 99 100 102 103 105 99 102 102 101

225 −f − − − − − − 221 227

General polymerization conditions: catalyst Y (10 μmol), [Y]/[Ph3C][B(C6F5)4]/[AliBu3] = 1/1/10 (mol/mol/mol), toluene (5 mL), [MTS + St]/[Y] = 500, Tp = 25 °C,unless otherwise noted. bMolar fraction of MTS in feed. cMolar fraction of MTS in copolymer. dDetermined by GPC in THF at 40 °C against polystyrene standard. eDetermined by DSC. fNot detected. g[MTS + St]/[Y] = 1000/1.

a

C

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product precipitated completely at the fourth stage when the obtained copolymer had a boarder molecular weight distribution than the previous three. The 13C NMR spectrum (Figure 3) showed clearly the singlet resonance at 145.10 and 142.11 ppm (o-dichlorobenzene as solvent) assigned to the ipso carbon atoms from the highly syndiotactic sPS and syndiotactic sPMTS sequences, respectively, suggesting the block copolymerization maintained the stereoselectivity of the catalyst system. The successful preparation of quarter-block copolymer proved the quasi-living character of this copolymerization and provided a direct way to obtain well-defined functionalized PS. Analysis of the 13C NMR Spectra of Copolymers. Because the statistical nature of copolymerization, whether the distinguished syndiotacticity of both monomer sequences maintained in the copolymerization was crucial and requisite to clear. Subjected to 13C NMR analyses, to our surprise, the copolymers (Table 2) exhibited more complicated and broad signals than the block sPS-b-sPMTS-sPS-b-sPMTS (Figure 3). Taking the ipso carbon on phenyl ring, for example, it appears as three peaks for St units but seven peaks for MTS units. With the increase of f MTS, α peak in the triplet became relatively weaker, while the β peak became relatively stronger in the “septuplet”. Similar phenomena were observed for the signals at ∼135, ∼127, ∼125, and ∼44 ppm (Figure S3). Obviously, assignment of these signals needed too much information. To simplify the analysis, the relatively clear and decisive three peaks at 145.27, 145.14, and 145.03 ppm were chosen for assignment. We assumed first that the chemical shift of a carbon from one monomer unit might be influenced by the two adjacent monomer units. Thus, the peaks at 145.27, 145.14, and 145.03 ppm can be attributed to the ipso carbon of St from SSS, SSM/ MSS, and MSM sequences, respectively (S stands for St unit and M stands for MTS unit). It can be proved directly by comparing the α peak in the 13C NMR spectrum of P(St-bMTS) and the ipso carbon of sPS in the spectrum of P(St-co-

methylthio group and the CC double bond to the active metal center significantly decreased the polymerization activity of MTS as compared to that of St (vide supra). This polar group privilege in the copolymerization environment, on the other hand, provided more chances for MST to attach the active centers, since the Lewis acid active metal cations preferred to be surrounded by the Lewis base methylthio polar groups to form a “cage” that obstructed the nonpolar St molecules approaching the active metal centers. Obviously, such a case was more severe at higher f MTS and was the reason why the activity of copolymerization decreased when f MTS increased.20 Note that this Lewis acid−base interaction just hampered the copolymerization rather than prohibited it; thus, even under a higher than 900:1 MTS-to-Y molar ratio, owing to the homogeneous nature of copolymerization as compared to the heterogeneous homopolymerization, a 100% conversion could be reached at last (Table 2, entry 10). To assign the microstructures of the copolymers, first, a quarter-block sPS-b-sPMTS-sPS-b-sPMTS copolymer was synthesized by sequentially alternating addition of equivalent St and MTS to the catalytic system. Samples isolated from every stage were characterized (Table 4). Each sample showed Table 4. Block Copolymerization of St and MTS stage

type

Mn (×104)

PDI

Tg (°C)

Tm (°C)

1 2 3 4

St St-MTS St-MTS-St St-MTS-St-MTS

3.1 5.8 7.3 9.2

1.4 1.5 1.6 2.2

92 103 99 103

266/270 252/263/270 252/260/268 242/253/260/267

a unimodal GPC curve (Figure S2), indicative of single active site in the process. The polymerization system became heterogeneous at the first stage of polymerization, however, which did not affect the proceeding of polymerization until the

Figure 3. 13C NMR spectra (C6D4Cl2) of statistical copolymer (upper) and the quarter-block copolymer (lower). D

DOI: 10.1021/acs.macromol.5b02263 Macromolecules XXXX, XXX, XXX−XXX

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and yttrium center in calculation. As mentioned before, this interaction would hinder the coordination of MTS in the later period of copolymerization, resulting in lower MTS conversion as well as lower MSM sequence than expected (Figure S4). Therefore, we can draw conclusion that the “triplet peaks” at 145 ppm were assigned to the ipso carbon in St units from three different kinds of sequences rather than the stereoerrors, indicating the perfect syndiospecific selectivity of the catalyst system remained in the copolymerization of MTS and St. Melting Point and Number-Averaged Sequence Length. The copolymers with f MTS = 10% and 90% (Table 2, entries 1 and 9) exhibit manifest melting points, which correlate to the sequential structures of a long major units separated by a single or short minor units. As the consequence, the melting point that comes from crystallization of finitelength segments is obviously lower than that of homopolymer. When the content of MTS increased, St segments became shorter and more difficult to crystallize (Table 2, entries 2−8) while the MTS segments became longer and came to crystallize (Table 2, entry 9). To explore the shortest crystallization lengths for both St and MTS segments, or the longest sequence lengths that fail to crystallize from the melt, a series of copolymers with continuously varied f MTS values were prepared (Table S1) to be calculated their number-averaged sequence lengths (n̅St or nM ̅ TS) according to the first-order Markov model.21a As seen from the combination DSC curves of PS, PMTS, and the copolymers (Figure 6), the melting point and

MTS) (Figure 4). The relative contents of these sequences were readily estimated by the solution and integration of 13C

Figure 4. 13C NMR spectra of copolymers with different monomer feed ratios (CDCl3) where the α peak assigned to sPS segment and β peak assigned to sPMTS segment.

Figure 6. DSC curves of polymers with different n̅St or nM ̅ TS.

the fusion enthalpy for sPS or sPMTS sequences decrease when n̅St or nM ̅ TS tends to be shorter until completely disappear at nS̅ t = 5.75 or nM ̅ TS = 8.11, corresponding to f MTS = 13.9% and 88.3%, respectively. The limit crystallization length of sPMTS segments was little longer than MTS because the bulkier MTS was more difficult to form ordered structure.

Figure 5. Relative integral ratios of the peaks at 145.27, 145.14, and 145.02 ppm in 13C NMR spectra and the calculation probability of SSS, SSM/MSS, and MSM triads with different f MTS.

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CONCLUSION In summary, we have demonstrated that the coordination polymerization of the polar monomer methylthiostyrene (MTS) by using an yttrium-based catalyst shows a remarkably high activity among the polar group substituted styrenic monomers to give also high molecular weight products with perfect syndiotacticity and narrow molecular weight distributions, which might be attributed to the weak coordination nature of the methylthio group to the active metal center and the similar NBO values between MTS and St. The copolymerization of MTS and St performed fluently under a broad range of monomer feed ratios in an even high activity and was capable of achieving complete conversion to afford the unprecedented statistical random copolymers of a polar and

NMR spectra as the observed values (Figure 5). On the other hand, it has been reported that the coordination polymerization of St follows the first-order Markov statistics,21 which is applicable to this copolymerization because of its quasi-living character. The relative occurrence probability of these sequences can be calculated according to the given reactivity ratios and f MTS (more calculation details are in the Supporting Information). The calculated and the observed values of the triad probability with f MTS matched quite well in both magnitude and tendency (Figure 5), except for a bit of differences which lied in the higher observed content of SSS sequence when f MTS < 0.5 and the lower observed content of MSM sequence when f MTS > 0.5. This exception was probably caused by ignoring the interaction between methylthio group E

DOI: 10.1021/acs.macromol.5b02263 Macromolecules XXXX, XXX, XXX−XXX

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[Ph3C][B(C6F5)4] (36.9 mg, 40 μmol, in 1 mL of toluene), a solution of complex (Flu-CH2-Py)Y-(CH2SiMe3)2(THF) (23.7 mg, 40 μmol, in 1 mL of toluene), and 1 mL of AliBu3 (0.5 mol/L) were added under a nitrogen atmosphere at 25 °C under stirring. Then, 0.5 mL of styrene solution (150.2 mg, 1 mmol in 1 mL of toluene) was added to initiate the polymerization. After 2 h, 0.5 mL of MTS solution (104.1 mg, 1 mmol in 1 mL of toluene) was added into the system, sequentially and polymerized for another 2 h. Such procedure was repeated once more, and the polymerization was terminated by HCl/ CH3OH. The precipitate was washed by ethanol and dried under vacuum at 40 °C to a constant weight.

nonpolar monomers, since the reactivity ratios for both monomers were very close to 1, and the kinetics followed the first-order Markov statistics. The reason behind this was the balance of the interaction between the methylthio group and the active metal center, which facilitates the coordination of MTS more in the initial polymerization stage while obstructing St less in the later period. The 13C NMR analysis showed that all the copolymers remained highly syndiotactic as homopolymers. By further process, the methylthio group could readily convert to the sulfhydryl or sulfonic group. This work provides a direct method of preparing highly syndiotactic as well as statistical functionalized sPS-based copolymers with controlled composition and distribution of the functional group.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.5b02263. Polymerization data of supplement experiments; NBO charges of different polar styrenic monomers; GPC curves of the block copolymer; NMR spectra; calculation methods of the first-order Markov statistics (PDF)

EXPERIMENTAL SECTION

General Material and Measurement. All manipulations were performed under a dried and oxygen-free nitrogen atmosphere using standard high-vacuum Schlenk techniques or in glovebox. Toluene, tetrahydrofuran, and n-hexane were distilled under nitrogen from sodium/benzophenone. Deuterated NMR solvents were purchased from Cambridge Isotopes, dried over Na (for C6D6) and molecular sieves (for CDCl3), and stored in the glovebox. Styrene (Aldrich) was dried by CaH2 under stirring for 48 h and distilled under reduced pressure before use. [Ph3C][B(C6F5)4] was synthesized following the literature procedures.22 1 H and 13C NMR spectra were recorded on a Bruker AV400 or 600 (FT, 400 or 600 MHz for 1H; 100 or 150 MHz for 13C) spectrometer. 1 H and 13C NMR spectra of polymer samples were recorded on a Bruker AV400 (FT, 400 MHz for 1H; 100 MHz for 13C) spectrometer in tetrachloroethane-d2. The molecular weight and molecular weight distribution of the polymers were measured by means of gel permeation chromatography (GPC) on a PL-GPC 220 type hightemperature chromatography equipped with three PL-gel 10 μm Mixed-BLS type columns at 150 °C. Differential scanning calorimetric (DSC) analyses were carried out on a Q100 DSC from TA Instruments under a nitrogen atmosphere. Synthesis of 4-(Methylthio)styrene. To a suspension of 37.9 g (112 mmol) of methyltriphenylphosphonium bromide in 250 mL of dry THF, 120 mmol of nBuLi (2.1 M solution in hexane) was added at 0 °C. When the solution became orange, 15.22 g (0.1 mol) of 4(methylthio)benzaldehyde was added dropwise to generate plenty of yellow precipitate immediately. The suspension was stirred for 12 h and terminated by saturated aqueous solution of ammonium chloride. The organic phase was separated and washed by saturated aqueous solution of NaCl and then dried over MgSO4 for 3 h. Removal of the solvent in a vacuum gave the residue that was purified by column chromatography on silica gel (petroleum ether) to give a pale yellow oil (12.6 g, 82%). 1H NMR (400 MHz, CDCl3): δ = 2.49 (s, 3H; CH3), 5.22 (d, J = 10.86 Hz, 1H; CH2-trans), 5.72 (dd, J = 17.60, 0.87 Hz, 1H; CH2-cis), 6.68 (dd, J = 17.59, 10.88 Hz, 1H; CH), 7.22 (d, J = 8.12 Hz, 2H; Ph), 7.34 (d, J = 8.21 Hz, 2H; Ph). 13C NMR (100 MHz, C6D6): δ = 15.66(1C; CH3), 113.09 (1C; CH2), 126.47 (2C; Ph), 126.59 (2C; Ph), 134.44 (1C; Ph), 136.18 (1C; CH), 138.05 (1C; Ph). Procedure for Copolymerization of 4-(Methylthio)styrene and Styrene (Table 3). A solution of [Ph3C][B(C6F5)4] (9.2 mg,10 μmol) in toluene (2.4 mL) was added to a solution of complex (FluCH2-Py)Y-(CH2SiMe3)2(THF) (5.9 mg, 10 μmol) in toluene (2.4 mL) in a 25 mL flask under a nitrogen atmosphere. The mixture was stirred at 25 °C for 1 min, and then 0.2 mL of AliBu3 (0.5 mol/L) was added. After 1 min, the mixture of styrene and 4-(methylthio)styrene (5 mmol in total) was added under moderate stirring. The reaction was terminated by adding a small amount of acidic methanol. The mixture was poured into ethanol (150 mL) to precipitate. The copolymer was collected by filtration. The precipitate was dried under vacuum at 40 °C to a constant weight. Procedure for Block Copolymerization of 4-(Methylthio)Styrene and Styrene (Table 4). To a 25 mL flask, a solution of

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AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected]; Fax (+86) 431 85262774; Tel +86 431 85262773 (D.C.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is partially supported by the NSFC for projects no. 21374112, 21304088, 51321062, and 21203073 and the MST for “973” project no. 2015CB654702.

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REFERENCES

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DOI: 10.1021/acs.macromol.5b02263 Macromolecules XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.macromol.5b02263 Macromolecules XXXX, XXX, XXX−XXX