Synthesis of Block Copolymers of Polyester and Polystyrene by Means

Jan 28, 2019 - Synthesis of B–A–B type triblock copolymers of aliphatic polyester (PEs) and polystyrene (PSt) was investigated by using cyclic uns...
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Synthesis of Block Copolymers of Polyester and Polystyrene by Means of Cross-Metathesis of Cyclic Unsaturated Polyester and Atom Transfer Radical Polymerization Ryouichi Okabayashi, Yoshihiro Ohta, and Tsutomu Yokozawa* Department of Materials and Life Chemistry, Kanagawa University, Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan

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ABSTRACT: Synthesis of B−A−B type triblock copolymers of aliphatic polyester (PEs) and polystyrene (PSt) was investigated by using cyclic unsaturated PEs prepared by conventional polycondensation of 4-octene-1,8-diol and sebacoyl chloride. The obtained cyclic PEs underwent cross-metathesis with PSt containing a carbon−carbon double bond (CC) at the central position, which was obtained by atom transfer radical polymerization (ATRP) of styrene with a bifunctional initiator containing a CC bond. PSt with a longer methylene spacer between the CC bond and PSt successfully afforded the PStb-PEs-b-PSt triblock copolymer. As another approach to obtain the triblock copolymer, cross-metathesis of cyclic PEs with 2butene-1,4-diol or 4-octene-1,8-diol bis(2-bromoisobutyrylate)s was conducted to afford linear PEs having ATRP initiation sites at both ends, followed by ATRP of styrene. The unsaturated PEs segment in the triblock copolymer obtained by the second approach was converted into a saturated PEs segment by treatment with tosyl hydrazide and tributylamine. DSC analysis of the triblock copolymer containing the saturated PEs segment showed crystallinity when the PEs content was ≥14 mol %.

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INTRODUCTION Block copolymers composed of two or more different polymer segments self-assemble in films and/or in solvents including water, and this self-assembly behavior is dependent on the molecular weight and the composition ratio of each segment.1−3 Block copolymers with controlled morphology are used in nanolithography,4−6 nanotemplating,7,8 storage media,9,10 and so on. The most general synthetic method for block copolymers11,12 is sequential polymerization of different monomers in one pot by using living polymerization methodology, such as addition polymerization13−18 and ring-opening polymerization.19−22 In addition, unique block copolymers have recently been obtained by means of postpolymerization modification of the polymer end groups.23−25 For example, many block copolymers of crystalline polyester (PEs) and noncrystalline polystyrene (PSt) have been synthesized by living ring-opening polymerization of lactone or lactide and living addition polymerization of styrene (St) via postpolymerization modification.26−40 However, there are only three reports about block copolymers of PEs and PSt, in which the PEs segment was synthesized by polycondensation: (i) radical polymerization of St, initiated from the end groups of PEs,41 (ii) coupling reaction of telechelic PEs and monofunctionalized PSt,42 and (iii) copolymerization of hydroxyl-terminated PSt, diol, and dicarboxylic acid chloride.43 The telechelic PEs in (i) and (ii) were prepared by the use of an excess of one of the two monomers in polycondensation, but the possibility of contamination with cyclic polymers cannot be ruled out because © XXXX American Chemical Society

intramolecular reaction of both chain ends occurs in competition with propagation, as described by Kricheldorf.44 We have recently reported a new approach to telechelic PEs free from contamination with cyclic polymer even in the case of polycondensation of A2 and B2 monomers.45 We first prepared cyclic PEs containing carbon−carbon double bonds (CC) in the backbone by means of polycondensation of unsaturated diol and dicarboxylic acid chloride,44,46 and the obtained cyclic PEs underwent cross-metathesis47−49 with symmetric olefin having two functional groups as an exchange reagent (ExR), affording PEs with functional groups at both ends. In the present work, we synthesized the PSt-b-PEs-b-PSt triblock copolymer by applying this approach based on cross-metathesis of cyclic PEs with ExR. We investigated two synthetic routes to the triblock copolymer. The first is cross-metathesis of cyclic PEs with PSt containing a CC bond in the middle of the backbone as a macro-ExR50 (Scheme 1a), and the second is atom transfer radical polymerization (ATRP) of St with PEs difunctional macroinitiator, which is obtained by cross-metathesis of cyclic PEs with ExR bearing ATRP initiation sites49,51−53 (Scheme 1b).

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RESULTS AND DISCUSSION Cross-Metathesis of Cyclic PEs with Macro-ExR Having PSt Chains. Synthesis of Macro-ExR Having PSt Chains. We Received: October 6, 2018 Revised: January 3, 2019

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DOI: 10.1021/acs.macromol.8b02147 Macromolecules XXXX, XXX, XXX−XXX

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Scheme 1. Synthesis of PSt-b-PEs-b-PSt Triblock Copolymer by Means of Cross-Metathesis and ATRP via (a) Macro-ExR for Cross-Metathesis and (b) Macroinitiator for ATRP

Scheme 2. Synthesis of ExR Having PSt Chains

Table 1. Synthesis of Macro-ExRs Having PSt Chainsa products b

entry

initiator

[Ini]0:[St]0:[PMDETA]0:[CuBr]0

reaction time (h)

conv of St (%)

1 2 3

1 2 2

1:100:2:2 1:100:2:2 1:200:2:2

29 24 46

61.4 50.5 66.4

PSt-1 PSt-2a PSt-2b

Mn(GPC)c

Mw/Mnc

Mn(MALS)d

6880 5880 14300

1.15 1.08 1.13

7100 6680 17200

ATRP of St with 1 or 2 was performed in the presence of PMDETA and CuBr in anisole (St/anisole = 1/1, v/v) at 70 °C. bDetermined by 1H NMR spectroscopy. cDetermined by GPC based on PSt standards (eluent: THF). dDetermined by division of the Mw value from MALS by the Mw/Mn ratio from GPC. a

first investigated cross-metathesis of cyclic PEs with PSt containing a CC bond as a macro-ExR for the synthesis of PSt-b-PEs-b-PSt triblock copolymer. To synthesize the macro-ExR having PSt chains, ATRP of St with initiator 154 or 2 was performed in the presence of 2 equiv of CuBr and N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) relative to the initiator in anisole (St/anisole = 1/1, v/v) at 70 °C (Scheme 2 and Table 1). In the polymerization using initiator 1, 100 equiv of St relative to 1 was polymerized for 29 h, yielding macro-ExR PSt-1 with Mn(MALS) of 7100 (MALS = multiangle light scattering) and Mw/ Mn of 1.15 (entry 1, Figure S1a). When initiator 2 was used, 100

and 200 equiv of St relative to 2 were polymerized for 24 and 46 h, yielding macro-ExR PSt-2a with Mn(MALS) of 6680 and PSt-2b with Mn(MALS) of 17200, respectively (entries 2 and 3, Figures S1b,c). The matrix-assisted laser desorption ionization time-offlight (MALDI-TOF) mass spectra of the products from 1 and 2 showed peaks due to PSt having a CC bond in the middle of the PSt backbone (Figures S2 and S3). Cross-Metathesis of Cyclic PEs with Macro-ExR. We next conducted cross-metathesis of cyclic unsaturated PEs with the prepared macro-ExR (Scheme 1a). Cyclic PEs were synthesized according to our previous report.45 B

DOI: 10.1021/acs.macromol.8b02147 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 2. Cross-Metathesis of Cyclic PEs with Macro-ExR PSt-1 or PSt-2a cyclic PEs entry 1 2 3 4b

cis cis cis trans

ExR

Mnc

Mw/Mnc

10900 13100 13100 21200

3.82 2.51 2.51 3.16

PSt-1 PSt-2a PSt-2a PSt-2b

block copolymer

Mnc

Mw/Mnc

[CC in PEs]0/ [ExR]0

6880 5880 5880 14300

1.15 1.08 1.08 1.13

100/20 100/20 100/10 100/5

reaction time (days) 5 4 4 4

BC-1a BC-2a BC-2b BC-2c

PEs/PSt molar ratio (wt ratio)d

Mnc

Mw/Mnc

5.6/94.4 (14.9/85.1) 8.1/91.9 (20.8/79.2) 6.5/93.5 (17.2/82.8)

6800 6490 6090 13600

1.20 1.18 1.24 1.30

a Cross-metathesis of cyclic PEs with macro ExR was performed in the presence of 1 mol % of G-II in dichloromethane ([CC in PEs]0 = 0.083 M) at rt. b1 mol % of HG-II was used instead of G-II. cDetermined by GPC based on PSt standards (eluent: THF). dDetermined by 1H NMR spectroscopy in CDCl3.

In the 1H NMR spectra, the olefinic proton signal of PSt-2a almost disappeared, and new signals attributable to adjacent PEs and PSt units appeared (Figure S10). These results indicated that triblock copolymers BC-2a,b were formed. When the feed ratio of PSt-2a was decreased from 20 to 10 mol %, the PEs content in the block copolymer was increased from 5.6 to 8.1%, as expected (entry 2 versus 3). However, the Mn value was decreased from 6490 to 6090. If only triblock copolymer had been formed, the molecular weight should have been increased; a longer PEs segment would be inserted between the PSt segments of macro-ExR. The observation of a small shoulder in the lower-molecular-weight region of the GPC trace of BC-2b, resulting in a broader Mw/Mn compared to that in the case of entry 2, implied that lower-molecular-weight cyclic PEs, formed by cross-metathesis between cyclic PEs due to decrease in the feed ratio of PSt-2a, might be present in BC-2b. This is presumably the reason for the decrease in the Mn value in entry 3 compared to that in entry 2. To synthesize higher-molecular-weight block copolymer, 5 mol % of higher-molecular-weight PSt-2b (Mn(GPC) = 14300) was reacted with cyclic PEs in the presence of 1 mol % of secondgeneration Hoveyda−Grubbs catalyst (HG-II),55 which does not introduce the terminal group from the catalyst into CC, in contrast to the case of G-II (entry 4). In the GPC elution curve of the products (BC-2c), the peak top was shifted toward the higher-molecular-weight region, indicating formation of triblock copolymer, and a shoulder was observed in the lower-molecularweight region compared with the peak of PSt-2b (Figure 1b). The shoulder peak is presumably due to cyclic PEs formed by cross-metathesis between cyclic PEs, as in the case of entry 3. ATRP of St with PEs Difunctional Macroinitiator. Synthesis of PEs Macroinitiator. We next investigated another route to the PSt-b-PEs-b-PSt triblock copolymer by means of ATRP of St with PEs difunctional macroinitiator as a more precise synthesis without ambiguity as to contamination with cyclic PEs (Scheme 1b). We first synthesized the PEs macroinitiator by cross-metathesis of cyclic PEs with ExR 1 or 2 containing ATRP initiation sites (Table 3). When 20 mol % of

When 20 mol % of PSt-1 relative to the repeat unit of PEs was reacted in the presence of 1 mol % of second-generation Grubbs catalyst (G-II), the Mn value of the product, estimated by GPC with a RI detector, was almost identical with that of PSt-1 (Table 2, entry 1, and Figure S7). The 1H NMR spectrum showed mainly olefinic proton signals due to cyclic PEs and PSt1, although small olefinic proton signals assignable to adjacent PEs and PSt units were observed (Figure S8). Furthermore, the MALDI-TOF mass spectrum showed peaks due to cyclic PEs and PSt-1 (Figure S9). Accordingly, the cross-metathesis of cyclic PEs with PSt-1 hardly proceeded, probably because the Grubbs catalyst could not readily approach the CC bond in PSt-1 due to the sterically hindered PSt chains around it. The decrease in the molecular weight of cyclic PEs is presumably attributed to cross-metathesis between cyclic PEs with entropy change as the driving force; a similar decrease in the molecular weight of cyclic PEs was observed in the cross-metathesis of cyclic PEs with a small amount of low-molecular-weight ExR.45 PSt-2 with longer methylene spacers was then used as a macro-ExR (entries 2 and 3). When 20 or 10 mol % of PSt-2a with Mn(GPC) of 5880 was reacted with cyclic PEs in the presence of 1 mol % of G-II, the GPC elution curves of the products were shifted toward the higher-molecular-weight region (Figure 1a).

Figure 1. GPC elution curves of (a) PSt-2a, BC-2a, and BC-2b and (b) PSt-2b and BC-2c.

Table 3. Cross-Metathesis of Cyclic PEs with ExR 1 or 2a cyclic PEs entry 1 2b 3

cis trans cis

linear PEs

Mnc

Mw/Mnc

d

ExR

[CC in PEs]0/[ExR]0

reaction time (days)

conv of ExR (%)

10900 21200 13100

3.82 3.16 2.51

1 1 2

100/20 100/5 100/20

4 5 5

100 100 ND

PEs-1a PEs-1b PEs-2

Mnc

Mw/Mnc

2470 12300 2920

1.70 1.43 1.71

a

Cross-metathesis of cyclic PEs with ExR was performed in the presence of 1 mol % of G-II in dichloromethane ([CC in PEs]0 = 0.17 M) at rt. 1 mol % of HG-II was used instead of G-II. cDetermined by GPC based on PSt standards (eluent: THF). dDetermined from the 1H NMR spectroscopy in CDCl3.

b

C

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Figure 2. GPC elution curves of (a) cis-cyclic PEs, (b) PEs-1a obtained by cross-metathesis with 20 mol % of 1 (Table 3, entry 1), (c) cis-cyclic PEs, and (d) PEs-2 obtained by cross-metathesis with 20 mol % of 2 (entry 3) and MALDI-TOF mass spectra of (e) PEs-1a (entry 1) and (f) PEs-2 (entry 3).

Table 4. ATRP of St with Macroinitiator PEs-1 or PEs-2a macroinitiator entry 1 2 3 4

PEs-1a PEs-1b PEs-1b PEs-2

block copolymer

Mnb

Mw/Mnb

[Ini]0:[St]0:[PMDETA]0: [CuBr]0

reaction time (h)

conv of St (%)

2470 12300 12300 2920

1.70 1.43 1.43 1.71

1:50:1:1 1:167:1:1 1:167:2:2 1:40:1:1

43 44 46 42

69.9 11.6 27.4 58.3

c

BC-1b BC-1c BC-1d BC-2d

PEs/PSt molar ratio (wt ratio)c

Mnb

Mw/Mnb

3.8/96.2 (10.5/89.5) 28.3/71.7 (54.0/46.0) 14.3/85.7 (33.2/66.8) 4.0/96.0 (11.2/88.8)

13700 14700 24000 15100

1.34 1.49 1.42 1.30

ATRP of St with macroinitiator PEs-1 or PEs-2 was performed in the presence of PMDETA and CuBr in anisole (St/anisole = 1/1, v/v) at 70 °C. Determined by GPC based on PSt standards (eluent: THF). cDetermined by 1H NMR spectroscopy in CDCl3.

a

b

ATRP of St from the End Groups of PEs. ATRP of St with macroinitiators PEs-1 and PEs-2 was conducted in the presence of 1 equiv of CuBr and PMDETA relative to the ATRP initiator site in anisole (St/anisole = 1/1, v/v) at 70 °C (Scheme 1b and Table 4). In the polymerization of St with PEs-1a, the GPC elution curve of the product was shifted toward the higher-molecularweight region from that of PEs-1a (Figure 3). In the 1H NMR spectrum, the olefinic proton signals b and c of ATRP initiator sites clearly disappeared, and new signals d and e attributable to olefinic protons of the initiator sites connected to PSt appeared (Figure 4). These data indicated that chain extension of St took place from the both initiation sites of PEs-1a, leading to triblock copolymer BC-1b (Table 4, entry 1). In the case of polymerization with PEs-1b (Mn = 12300), the conversion of St was low, and the Mn value of the product (BC-1c) was increased only by 2400 (entry 2, Figure S20b). Because this result might be due to low concentrations of the initiation sites and catalyst, ATRP was then performed by using double the amounts of PMDETA and CuBr, affording triblock copolymer

1 and 1 mol % of G-II relative to the repeat unit of PEs were used (entry 1), the 1H NMR spectrum of the product showed consumption of 1 (Figure S12), and the GPC elution curve was shifted toward the lower-molecular-weight region (Mn = 2470) (Figure 2a,b). In the MALDI TOF mass spectrum, essentially a single series of peaks due to linear PEs having the ATRP initiation sites at both ends (PEs-1a) were observed (Figure 2e). Similarly, cross-metathesis of cyclic PEs with 5 mol % of 1 and 1 mol % of HG-II was carried out, affording PEs-1b with higher molecular weight (Mn = 12300) (entry 2, Figures S14−S17). When ExR 2 with a longer methylene spacer was used, lowmolecular-weight polymer was similarly obtained (entry 3, Figure 2c,d). The MALDI-TOF mass spectrum showed one series of peaks due to linear PEs having the ATRP initiation sites at both ends (PEs-2) (Figure 2f), although the conversion of 2 could not be determined from the 1H NMR spectrum because the olefinic proton signal of 2 was not distinguishable from that of the unit connected to PEs after the cross-metathesis of 2 (Figure S18). D

DOI: 10.1021/acs.macromol.8b02147 Macromolecules XXXX, XXX, XXX−XXX

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polymers. In the case of BC-1b, which has the lowest PEs ratio (PEs/PSt = 3.8/96.2), the DSC curve did not show Tm and Tc, but there was a clear Tg at 63.5 °C and an ambiguous Tg at −1.5 °C. Although unsaturated PEs homopolymer showed Tm = 40.0 °C and Tc = 28.5 °C (Figure S27), the short PEs segment in the block copolymer with PSt was not crystallized but presumably decreased the Tg of the PSt segments due to partial compatibility between PEs and PSt. BC-1b-H showed a similar tendency (Figure 5a). Even BC-1c, which has the highest PEs ratio (PEs/PSt = 28.3/71.7), did not show crystallinity but exhibited Tg at −25.7 and −6.0 °C, whereas BC-1c-H showed Tm at 53.1 °C in the heating process and Tc at 33.9 °C in the cooling process; no obvious Tg was observed (Figure 5b). Therefore, it turned out that the saturated PEs segment in the block copolymer with PSt had higher crystallinity, in contrast to the case of unsaturated PEs. Similarly, BC-1d (PEs/PSt = 14.3/85.7) with higher molecular weight did not show crystallinity but exhibited a clear Tg at 43.3 °C and an ambiguous Tg at −10.7 °C, whereas BC-1dH showed crystallinity (Tm = 54.9 °C and Tc = 28.6 °C) (Figure 5c).

Figure 3. GPC elution curves of (a) macroinitiator PEs-1a and (b) BC1b obtained by ATRP of St with PEs-1a (Table 4, entry 1).

with Mn = 24000 (BC-1d) (entry 3, Figure S20c). When PEs-2 was used, block copolymer (BC-2d) with Mn = 15100 was obtained, as in the case of ATRP with PEs-1a (entry 4, Figure S20e). Thermal Analysis of Block Copolymers. Hydrogenation of Block Copolymers. Hydrogenation of the CC bond in the obtained block copolymers was carried out, and the thermal properties of the products were compared with those of the original block copolymers containing the unsaturated PEs segment by means of differential scanning calorimetry (DSC). Conventional hydrogenation of CC with palladium on carbon under a hydrogen atmosphere would be difficult due to the very slow adsorption of CC on the catalyst because of the steric hindrance of the polymer chain. Accordingly, the obtained BC-1b−1d were reacted with tosyl hydrazide and tributylamine in o-xylene under reflux (Scheme 3).56 The 1H NMR spectra of the products showed that 98% of CC in the PEs backbone was hydrogenated in the cases of BC-1c and BC-1d, which have relatively high ratios of PEs (Figures S24 and S25). On the other hand, only 78% of the CC in BC-1b, which has a lower PEs ratio, was hydrogenated (Figure S26). DSC Measurement. DSC analysis of block copolymers BC-1 and hydrogenated BC-1-H was conducted (Table 5). BC-1b and BC-1b-H were both powdery polymers. BC-1c,d were sticky polymers, whereas BC-1c-H and BC-1d-H were powdery

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CONCLUSIONS We investigated two approaches to the synthesis of PSt-b-PEs-bPSt triblock copolymer as an application of our recently developed cross-metathesis of cyclic unsaturated PEs, which is easily obtained by conventional polycondensation of unsaturated diol and diacid chloride, with functionalized ExR, leading to linear PEs bearing functional groups at both ends. In the first approach, cyclic unsaturated PEs underwent crossmetathesis with PSt macro-ExR having a CC bond in the central position of the backbone, which was obtained by ATRP of St with a bifunctional initiator containing a CC bond. PSt macro-ExR with a shorter methylene spacer between CC and PSt failed to undergo cross-metathesis, whereas a longer methylene spacer in PSt macro-ExR enabled cross-metathesis, affording PSt-b-PEs-b-PSt triblock copolymer. However, attempts to synthesize the higher-molecular-weight block

Figure 4. 1H NMR spectra of (a) macroinitiator PEs-1a and (b) BC-1b obtained by ATRP of St with PEs-1a (Table 4, entry 1) in CDCl3 at 25 °C. E

DOI: 10.1021/acs.macromol.8b02147 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Scheme 3. Hydrogenation of BC-1 with Tosyl Hydrazide and Tributylamine

Table 5. DSC Analysis of BCsa BC-1b BC-1b-H BC-1c BC-1c-H BC-1d BC-1d-H

PEs/PSt molar ratio (wt ratio)

Mn(GPC)b

Mn(MALS)c

Tga (°C)

3.8/96.2 (10.5/89.5)

13700 11200 14700 13400 24000 13400

18000 14100 11900 16400 22300 23300

−1.5, 63.5 −31.4, 45.1 −25.7, −6.0

28.3/71.7 (54.0/46.0) 14.3/85.7 (33.2/66.8)

Tma (°C)

Tca (°C)

53.1

33.9

54.9

28.6

−10.7, 43.3

Determined by DSC at the heating/cooling rate of 10 °C/min under a nitrogen atmosphere. bDetermined by GPC based on PSt standards (eluent: THF). cDetermined by division of the Mw value from MALS by the Mw/Mn ratio from GPC.

a

Figure 5. DSC curves of (a) BC-1b and BC-1b-H, (b) BC-1c and BC-1c-H, and (c) BC-1d and BC-1d-H at the heating/cooling rate of 10 °C/min under a nitrogen atmosphere.

copolymer by decreasing the amount of PSt macro-ExR resulted in contamination with low-molecular-weight cyclic PEs, presumably formed by cross-metathesis between cyclic PEs. In the second approach, cyclic unsaturated PEs underwent cross-metathesis with a symmetrical alkene having two ATRP initiation sites, affording linear PEs with the ATRP initiation sites at both ends. The obtained macroinitiator was used for

ATRP of St to yield a variety of PSt-b-PEs-b-PSt triblock copolymers, depending upon the feed ratio of St. This approach was superior to the former one in terms of suppression of contamination of cyclic PEs. The CC bond in the PEs segment of these copolymers was hydrogenated by treatment with tosyl hydrazide and tertiary amine. DSC analysis of the block copolymers before and after F

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mmol of Grubbs catalyst in dry dichloromethane were added to the flask successively via a syringe, and the reaction mixture was stirred at room temperature for 4−5 days (aliquots of the reaction mixture were taken 5 times during the reaction). The reaction was quenched by addition of 0.02 mL of ethyl vinyl ether. The mixture was stirred for 2 h and then concentrated in vacuo to afford a crude product, which was dissolved in dichloromethane and precipitated into methanol. The precipitate was collected by filtration on Celite and dissolved in dichloromethane. The resulting solution was evaporated in vacuo to afford pure block copolymer. Synthesis of PEs Macroinitiator. Typical Procedure of CrossMetathesis of Cyclic PEs with ExR 1 or 2. Cyclic polyester (0.2 mmol of repeat unit) was added to a round-bottomed flask, and the atmosphere in the flask was replaced with argon. 0.6 mL of degassed solution of an ExR in dry dichloromethane was added to the flask via a syringe (the ratio of the added ExR to PEs was varied). 0.56 mL of degassed solution of 0.002 mmol of Grubbs catalyst in dry dichloromethane was added to the flask via a syringe, and the reaction mixture was stirred at room temperature for 4−5 days. The reaction was quenched by addition of 0.04 mL of ethyl vinyl ether. The mixture was stirred for 2 h and then concentrated in vacuo to afford a crude product, which was purified by preparative HPLC with SEC columns to remove low-molecular-weight compounds. When 5 mol % of 1 relative to CC in the cyclic PEs was used (Table 3, entry 2), the resulting linear PEs were dissolved in dichloromethane and precipitated into methanol after purification by HPLC. The precipitate was collected by filtration on Celite and dissolved in dichloromethane. The resulting solution was evaporated in vacuo to afford pure PEs. ATRP of St from the End Groups of PEs. General Procedure of ATRP of St from the Introduced End Groups of PEs. A Schlenk tube equipped with a magnetic stirring bar was charged with macroinitiator, PMDETA, styrene (the ratio of these reagents was varied), and dry anisole (same volume as styrene). The solution was degassed three times by means of freeze−pump−thaw cycles, the vessel was filled with argon, and then CuBr was added to the solution. The reaction mixture was degassed three times by means of freeze−pump−thaw cycles, and the vessel was filled with argon again before being sealed with a stopper. The reaction mixture was stirred at 70 °C for 2 days, and the reaction was quenched by cooling with liquid nitrogen. The reaction mixture was passed through a column containing active neutral alumina (eluent: THF) to remove copper, and the eluate was dried in vacuo. The crude block copolymer was dissolved in THF or dichloromethane and precipitated into methanol. The precipitate was collected by filtration on Celite and dissolved in dichloromethane. The resulting solution was evaporated in vacuo to afford pure block copolymer. Hydrogenation of Block Copolymers. Typical Procedure of Hydrogenation of CC in Block Copolymers. Block copolymer BC1c (20.8 mg) and tosyl hydrazide (28.7 mg, 0.154 mmol) were added to a round-bottomed flask. A solution of 2,6-di-tert-butyl-p-cresol (0.02 mg, 9.1 × 10−5 mmol) and tributylamine (0.0385 mL, 0.162 mmol) in o-xylene (0.35 mL) was added to the flask; the mixture was refluxed for 2 h, then cooled to room temperature, and washed with water three times. The organic layer was precipitated into methanol. The precipitate was collected by filtration on Celite and dissolved in dichloromethane. The resulting solution was concentrated under reduced pressure. The residue was similarly precipitated into methanol and then hexane. The residue was collected by filtration on Celite and dissolved in dichloromethane. The resulting solution was evaporated in vacuo to afford pure hydrogenated block copolymer as a white translucent resin (17.4 mg, 84%).

hydrogenation indicated that the block copolymer containing the unsaturated PEs segment did not show crystallinity, whereas the block copolymer containing 14 or 23 mol % saturated PEs segment clearly showed Tm = 53−55 °C. Because unsaturated PEs homopolymer shows crystallinity (Tm = 40.0 °C), it turned out that crystallization of the unsaturated PEs segment was disturbed in the block copolymer with PSt, whereas the saturated PEs segment showed crystallinity in the block copolymer with PSt. Other features of block copolymers of PEs and PSt are under investigation.

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EXPERIMENTAL SECTION

Materials. All starting materials were purchased from commercial suppliers (TCI, Aldrich, Wako, and Kanto). Styrene was passed through a short column filled with neutral aluminum oxide just before use to remove stabilizer. Other starting materials were used without further purification. Commercially available dehydrated anisole (Aldrich) and dichloromethane (Kanto) were used as dry solvents. The synthetic procedures for monomers, cyclic PEs, (Z)-but-2-ene-1,4diyl bis(2-bromo-2-methylpropanoate) (1), and (Z)-oct-4-ene-1,8-diyl bis(2-bromo-2-methylpropanoate) (2) are described in the Supporting Information. General. 1H and 13C NMR spectra were obtained on JEOL ECA500 and ECA-600 spectrometers. The internal standard for 1H NMR spectra in CDCl3 was tetramethylsilane (0.00 ppm), and the internal standard for 13C NMR spectra in CDCl3 was the midpoint of CDCl3 (77.0 ppm). The Mn and Mw/Mn values of polymers were measured on a Shodex GPC-101 gel permeation chromatography unit (eluent, THF; calibration, polystyrene standards) with two Shodex KF-804L columns and Shodex UV-41, Shodex RI-71S, and Wyatt Technology DAWN EOS multiangle light scattering (MALS, Ga−As laser, 11/4 690 nm) detectors. The Mn(MALS) value was also calculated by division of the Mw from MALS by the Mw/Mn ratio from GPC. Purification of PEs after the cross-metathesis was conducted with a Shimadzu LC-6AD preparative HPLC (eluent: THF, flow rate: 5.0 mL/min) equipped with two TOSOH TSKgel columns (2 × GMHHR-H) and Shimadzu SPD-10A and Shimadzu RID-10A detectors. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra were recorded on a Shimadzu/Kratos AXIMA-CFR plus in the reflectron mode by use of a laser (λ = 337 nm). Dithranol (1,8-dihydroxy-9[10H]anthracenone) was used as the matrix for the MALDI-TOF mass measurements. Differential scanning calorimetry (DSC) analyses were performed on a Hitachi X-DSC7000 calorimeter from −90 to 140 °C at heating/cooling rate of 10 °C/min under a nitrogen atmosphere. All glass apparatus was dried prior to use. All reactions were conducted under an inert gas atmosphere. Synthesis of Macro-ExR Having PSt. General Procedure of ATRP from 1 or 2. A Schlenk tube equipped with a magnetic stirring bar was charged with 1 equiv of the initiator (1 or 2), 2 equiv of PMDETA, 100 or 200 equiv of styrene, and dry anisole (same volume as styrene). The solution was degassed three times by means of freeze−pump−thaw cycles, the vessel was filled with argon, and then 2 equiv of CuBr was added to the solution. The reaction mixture was degassed three times by means of freeze−pump−thaw cycles, and the vessel was filled with argon again before being sealed with a stopper. The solution was stirred at 70 °C for a predetermined time, and the reaction was quenched by cooling with liquid nitrogen. The reaction mixture was passed through a column containing active neutral alumina (eluent: THF) to remove copper, and the eluate was dried in vacuo. The crude PSt was dissolved in THF or dichloromethane and precipitated into methanol. The precipitate was collected by filtration on Celite and dissolved in dichloromethane. This solution was evaporated in vacuo to afford pure macro-ExR. Cross-Metathesis of Cyclic PEs with Macro-ExR. General Procedure of Cross-Metathesis of Cyclic PEs with Macro-ExR. Cyclic PEs (0.1 mmol of repeat unit) and a macro ExR were added to a roundbottomed flask (the ratio of the added ExR to PEs was varied), and the atmosphere in the flask was replaced with argon. Then 0.8 mL of degassed dichloromethane and 0.4 mL of degassed solution of 0.001

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b02147. Synthetic procedure of monomers, ExR and cyclic PEs, GPC elution curves, 1H NMR spectra, and MALDI-TOF G

DOI: 10.1021/acs.macromol.8b02147 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules

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mass spectra of the obtained macro-ExR, macroinitiators, and block copolymers (PDF)

AUTHOR INFORMATION

Corresponding Author

*(T.Y.) E-mail: [email protected]. ORCID

Tsutomu Yokozawa: 0000-0003-2536-6271 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by the MEXT-Supported Program for the Strategic Research Foundation at Private Universities (No. S1311032), 2013−2018.

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DOI: 10.1021/acs.macromol.8b02147 Macromolecules XXXX, XXX, XXX−XXX