Article pubs.acs.org/Macromolecules
Highly Cis-1,4-Selective Living Polymerization of 3‑Methylenehepta1,6-diene and Its Subsequent Thiol−Ene Reaction: An Efficient Approach to Functionalized Diene-Based Elastomer Lei Li,†,‡ Shihui Li,† and Dongmei Cui*,† †
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China ‡ University of the Chinese Academy of Sciences, Changchun Branch, Changchun 130022, People’s Republic of China S Supporting Information *
ABSTRACT: Living polymerization of 3-methylenehepta-1,6-diene (MHD) catalyzed by bis(phosphino)carbazoleide-ligated yttrium alkyl complex afforded a new product bearing pendant terminal vinyl groups with high stereotacticity (cis-1,4-selectivity up to 98.5%), proved by the NMR (1H, 13C, and 1D ROESY) spectroscopic analyses, which demonstrates overwhelmingly favorable chemoselectivity toward conjugated diene over α-olefin moieties. High cis-1,4 random copolymers of MHD and isoprene could also be obtained with pendant vinyl groups ranging from 10% to 90%. These vinyl groups in every chain unit can be cleanly and quantitatively converted into various functionalities via light-mediated thiol−ene reaction, resulting in homo- and copolymers of various functional butadiene derivatives, which display versatile thermal properties.
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conditions on the microstructure of the resulting polymer.5 Stadler et al. opened the door to access N,N-dialkyl-2aminomethyl-1,3-butadiene polymers through anionic and radical polymerization techniques and further quaternized the tertiary amino groups to obtain ionic polymers.6 Sheares and co-workers expanded the butadiene derivatives to those containing cyano, ester, or asymmetric amino polar groups and investigated their radical polymerization kinetics.4a,b,7 The employed radical or anionic active species show poor control in stereoregularity, while most of these functional groups are poisonous to the specific selective coordination polymerization catalysts; thus to prepare highly regulated diene-based polymers carrying a large variety of functional groups is still an obvious challenge. The chemical modification of well-defined prepolymers (e.g., “reactive polyolefin intermediate” approach developed by Chung8) is a valuable alternative to the traditional route of
INTRODUCTION
Incorporation of functionality such as carboxyl, hydroxyl, and siloxyl groups into nonpolar polymer materials has been a research target in polymer science for many decades, since it may endow the materials many desirable properties, such as permeability, compatibility, and adhesiveness.1 This seems more important and necessary in some cases for conjugated diene-based elastomers to make new “long life” and “high performance” tires by means of mixing with other polar polymers such as polyamides and polyesters as well as organic and inorganic fillers such carbon black and silica.2 These functional polymers can be prepared either by direct polymerization of functionalized butadiene derivatives or by postpolymerization modification.3 Since butadiene derivatives bearing electronically withdrawing polar groups are difficult to be synthesized, and easily dimerized to form Diels−Alder adduct during polymerization process, the (co)polymerization of polar butadiene derivatives has been far from successful.4 Hirao and Takenaka reported the anionic living polymerization of a series of silicon-containing butadiene derivatives and systematically investigated the influences of polymerization © XXXX American Chemical Society
Received: December 7, 2015 Revised: January 22, 2016
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DOI: 10.1021/acs.macromol.5b02654 Macromolecules XXXX, XXX, XXX−XXX
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cholesterol.9e−i Hazer improved the mechanical properties and hydrophilic character of the biodegradable poly(3-hydroxyalkanoate) by clicking hydroxyl or carboxyl groups into the side chains through thiol−ene reaction.9n Up to now, the synthesis of 1,4-stereoregulated butadiene-based polymers bearing vinyl group and their potential in further functionalization remains unexplored. In this report, we present the synthesis of 3-methylenehepta1,6-diene (MHD) and its highly cis-1,4-selective living (co)polymerization catalyzed by bis(phosphino)carbazoleide-ligated yttrium complex,13 which shows overwhelmingly favorable chemoselectivity toward conjugated diene over the α-olefin moiety. Via thiol−ene click reaction of the pendant vinyl group, highly cis-1,4-regulated polybutadiene derivatives with various polar groups and tunable functional degrees were obtained for the first time. Their unique thermal properties were also investigated.
Chart 1. Structure of the Bis(phosphino)carbazolide-Ligated Yttrium Complex 1
direct (co)polymerization of functional monomers. Chain length and microstructures of polymer can be controlled by living and stereoselective polymerization of monomers carrying reactive but innocent groups while the functionalization can be controlled by the modification conditions. Monomers containing terminal vinyl groups meet such conditions quite well, and the resulting polymers have received great attention as building blocks to access functional and topological polymers through versatile reactivity of the featured double bonds, including epoxidation, hydrosilylation, hydroboration, thiol−ene reaction, and Heck coupling reaction of the pendent vinyl group.9 Among these, thiol−ene click reaction is quickly gaining popularity as a powerful and versatile method because of its quantitative conversion, rapid reaction rates, insensitiveness to ambient oxygen or water, and ready availability of an enormous range of thiols.10 Nomura and co-workers introduced polar functionalities via terminal olefinic double bonds on the side chains of poly(1,7-octadiene).11 Pan et al. realized functionalization of isotactic polypropylene via copolymerization of propylene with p-(3-butenyl)styrene bearing reactive double bonds.12 Schlaad has utilized thiol−ene reaction to functionalize 1,2-selective polybutadiene with a large toolbox of polar groups including hydrophilic acid, amine, cysteine derivatives, amino acid, dihydroxy, glucose, nonhydrophilic esters, and
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RESULTS AND DISCUSSION Homopolymerization of 3-Methylenehepta-1,6-diene (MHD). The monomer 3-methylenehepta-1,6-diene (MHD) was synthesized with the similar protocol of amino-functionalized butadiene reported in the literature4b through Kumada coupling reaction with an overall yield of 45%. MHD was polymerized smoothly by the bis(phosphino)carbazoleideligated yttrium complex 1 (Chart 1) upon activation of [Ph3C][B(C6F5)4] to afford a rubber-like material in high activity. The 1H NMR spectrum of the resultant polymer shows a strong triplet at 5.14 ppm for the olefinic hydrogen H3 (−CH2−CHC(R)−CH2−), indicating a high 1,4-regioregularity (Figure 1). To determine the cis/trans configuration of the backbone carbon−carbon double bonds, additional 1D selective ROESY (rotating-frame Overhauser spectroscopy) experiments were performed. Irradiation of H3 revealed the through-space interaction with H8 (Figure 2, top), and reverse
Figure 1. 1H NMR (400 MHz, CDCl3, 25 °C) spectrum of PMHD (Table 1, entry 1). B
DOI: 10.1021/acs.macromol.5b02654 Macromolecules XXXX, XXX, XXX−XXX
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Figure 2. 1D ROESY selective irradiation upon H3 showing H3−H8 through-space interaction (top) and upon H8 showing H8−H3, H8−H8′, and H8−H7 through-space interactions (bottom).
irradiation of H8 revealed the through-space interaction of H8− H3, thus establishing that H3 was located pointing to the dangling olefinic hydrogen H8 as in cis-configured PMHD (in a trans-1,4-selective polymer there would be no through-space interaction between H3 and H8). 13C NMR analysis exhibited the relative amount of cis/trans microstructures, and the cis-1,4content of the resulting PMHD was determined to be up to 98.5% with trifling amount of 3,4-configuration (1.5%).14 The cis-1,4-selectivity was barely affected by addition of aluminum alkyls into the binary catalyst system, which could not be
further enhanced over 98.5% by lowering the polymerization temperature. Increasing the monomer-to-initiator feeding ratio from 250:1 to 1000:1 resulted in proportional increase of the molecular weights, close to the theoretical ones, while the molecular weight distributions remained narrow, indicating a livingness polymerization mode, in line with the living isoprene polymerization by using the same catalytic system reported by us previously (Figure 3).13 Thermal analysis of the resultant PMHD revealed a glass transition temperature Tg of −82.3 °C, which is much lower than the highly cis-1,4-regulated C
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Macromolecules polyisoprene (−64 °C) and other substituted polybutadiene products.4a,b,7b,15 This drop of Tg can be attributed to the presence of flexible butenyl side chains in PMHD homopolymers, which may act as plasticizer, adding to the free volume of the polymer chains. Copolymerization of MHD and Isoprene. The copolymerization of MHD and isoprene was probed first under various MHD-to-IP feeding ratios increasing gradually from 50:450 to 450:50. In all cases, the copolymerization performed fluently to achieve almost full conversion in 20 min. The resulting copolymers possessed compositions very close to the monomers’ feeding ratio, implying identical incorporation rates in the copolymerization process. The molecular weight of the
copolymer structures, with dumpy and split peaks of backbone carbon atoms for the former and sharp single peaks for the latter (Figure S2). These results demonstrated that the chain structure and composition of the resulting copolymer could be facilely tuned by either changing the feeding mode or varying the feeding ratio of comonomers. Functionalization of MHD (Co)polymer via Thiol−Ene Reaction. Versatile reactivities of the pendant vinyl groups render the resulting MHD (co)polymers highly promising candidates for postmodification. The heat-initiated thiol−ene process was first attempted by stirring the THF solution of PMHD (Table1, entry 1) with 5 equiv of 3-(trimethoxysilyl)propane-1-thiol and catalytic amount of AIBN at 60 °C overnight. The overall functionalization degree was less than 80%. Extending the reaction time led to unpleasant gelation before the full conversion, which may be caused by the enhanced activity of the backbone double bonds relative to the pendant ones at elevated temperature.17 Then the light-initiated thiol−ene reaction between the polymer (Table1, entry 1) and thiol was performed in THF with 365 nm ultraviolet (UV) light. With catalytic amount of photoinitiator 2,2-dimethoxy-2phenylacetophenone (DMPA), the thiol−ene reaction readily went into completion within 2 h (Table 3, entry 1), which was clearly illustrated in the 1H NMR spectrum of the resulting polymer (Figure 5). The peaks corresponding to the pendant vinyl group, originally at around 4.91 and 5.79 ppm, disappear. New peaks correlating to the newly formed thioether link at 2.49 and 3.55 ppm are ascribed to the methylene protons adjacent to sulfur atom and the trimethoxysilyl group, respectively. Meanwhile, the resonances of the olefinic protons of the main chain at 5.13 ppm remain, indicating that the backbone microstructure stays intact. GPC curves of functional PMHD shift to high molecular weight with monomodal distribution without any trace of shoulder peak (Figure 6), indicating the absence of side reactions such as interchain coupling. The resulting material may be regarded as a homopolymer of trimethoxysilyl-containing butadiene derivatives, a promising product of grafting onto inorganic materials such as silica,5b,18 one of the most important fillers to reduce tire’s rolling friction and increase the strength. We also noted that although the trimethoxysilyl-functionalized polymer was stable in water at work-up, it became insoluble in most solvent after storage in moist air for about a week, indicating slow hydrolysis of methoxysilyl groups and subsequent condensation
Figure 3. GPC traces of the resulting PMHD under various feeding ratios of MHD/Cat. (Table 1, entries 1−4).
copolymer was close to the theoretic one while maintaining the narrow molecular weight distributions, indicating that the copolymerization maintained the living polymerization mode as the homopolymerizations of both monomers. Meanwhile, single glass transition temperatures were observed on the DSC curves, varying from −68.4 to −81.0 °C with increased MHD contents in the copolymer, in accordance with theoretical ones calculated by the empirical Fox equation,16 which confirmed the random copolymer structure. Sequential addition of two monomers led to the expected block microstructure with two Tgs at −79.7 and −67.0 °C, respectively, slightly deviating from those of the homopolymers. The 13C NMR spectra of the copolymer samples clearly illustrate the differences between random and diblock
Figure 4. DSC curves of the MHD and isoprene random copolymers in Table 2 (entries 1−5). D
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Macromolecules Table 1. Homopolymerization of 3-Methylenehepta-1,6-diene (MHD) Catalyzed by Complex 1a entry
feed ratio MHD/Cat.
temp (°C)
time (min)
yield (%)
cis-1,4b (%)
Mn,calcd (×10−4)c
Mn,GPC (×10−4)d
PDId
1 2 3 4 5e 6f 7
250/1 500/1 750/1 1000/1 250/1 250/1 250/1
25 25 25 25 25 25 −20
5 15 30 60 5 5 600
100 100 96 98 100 100 94
98.5 98.5 98.5 98.5 98.5 98.5 98.5
2.70 5.40 7.78 10.6 2.70 2.70 2.54
3.29 5.92 8.53 12.1 3.01 2.88 3.62
1.12 1.09 1.06 1.08 1.10 1.09 1.25
Polymerization conditions: [monomer] = 1 mol L−1, in toluene; Cat. = 10 μmol; borate ([Ph3C][B(C6F5)4]) = 10 μmol. bCis-1,4-selectivity of PMHD determined by 1H and 13C NMR analyses. cTheoretical molecular weight calculated by the equation Mn,calcd = MMHD × ([MHD]/[Cat.]) × yield, MMHD = 108. dDetermined by GPC in THF using polystyrene as standard. eAliBu3 (50 μmol) was added into the catalytic system. fAlMe3 (50 μmol) was added into the catalytic system. a
Table 2. Copolymerization of 3-Methylenehepta-1,6-diene (MHD) and Isoprenea entry
feed ratio MHD/IP/Cat.
time (min)
yield (%)
1 2 3 4 5 6g
50/450/1 150/350/1 250/250/1 350/150/1 450/50/1 250/250/1
20 20 20 20 20 20 (MHD) + 20 (IP)
98 96 93 96 92 93
CNHD, CIPb (%) 10, 29, 50, 70, 89, 50,
Tgf (°C)
Mn,calcd (×10−4)c
Mn,GPC (×10−4)d
PDId
Tge (°C)
3.60 3.98 4.40 4.80 5.18 4.40
4.02 4.60 4.93 5.21 5.83 4.79
1.12 1.18 1.19 1.08 1.12 1.17
−68.4 −71.3 −74.3 −77.3 −81.0 −79.7/−67.0
90 71 50 30 11 50
−66.5 −71.2 −75.3 −78.6 −81.2
a Polymerization conditions: [MHD] + [IP] = 1 mol L−1, in toluene; Cat. = 10 μmol; borate ([Ph3C][B(C6F5)4]) = 10 μmol. bContent of MHD (CNHD) and IP (CIP) in the copolymer determined by 1H NMR analysis. cTheoretical molecular weight calculated by the equation Mn,cacld = MMHD × ([MHD]/[Cat.]) × CMHD × yield + MIP × ([IP]/[Cat.]) × CIP × yield, MMHD = 108, MIP = 68. dDetermined by GPC in THF using polystyrene as standard. eGlass transition temperature (Tg) determined by DSC (heating rate: 10 °C min−1, second scan). fTheoretical values calculated by the Fox equation. gSequential addition of 250 equiv of MHD and then 250 equiv of isoprene.
Table 3. Postmodification of PMHD with Various Thiol Compoundsa entry
thiol
time (h)
FDb (%)
Mn,GPC (×10−4)c
PDIc
Tgd (°C)
1 2 3 4 5 6 7 8 9
3-(trimethoxysilyl)propane-1-thiol β-mercaptoethanol 1-thioglycerol 3-mercaptopropanoic acid methyl 3-mercaptopropionate N-acetyl-L-cysteine phenylmethanethiol (4-methoxyphenyl)methanethiol cysteamine
2 10.5 8 1 3 1 12 12 48
100 100 100 100 100 100 100 100 8
6.35 n.d.f n.d.f n.d.f 7.02 n.d.f 5.58 6.01 n.d.g
1.32 n.d.f n.d.f n.d.f 1.43 n.d.f 1.34 1.22 n.d.g
−78.4 −43.1 −53.2 −32.3 −68.1 45.1 −41.6 −30.3 n.d.g
Tmd (°C)
50.1
n.d.g
WCAe (deg) 85.1 81.7 70.2 35.9 78.1 21.4 98.5 90.5 n.d.g
Conditions: 2 mg of photoinitiator DMPA, 60 mg of PMHD, thiol (5 mol equiv of pendant double bonds), 5 mL of THF, T = 25 °C, UV light intensity (1.42 mW/cm2). bFunctionalization degrees (%) established by 1H NMR spectra. cDetermined by GPC in THF using polystyrene as standard. dGlass transition temperature (Tg) or melting temperature (Tm) determined by DSC (heating rate: 10 °C min−1, second scan). eStatic water contact angle (WCA) measured using sessile method. The WCA of pure PMHD was 100.2°. fMolecular weights and molecular weight distributions of these hydroxyl-containing thiol functionalized PMHD were not determined because polymers with densely grafted hydroxyl groups in THF solution bind to the GPC column, and hence no peaks were observed at normal elution time in GPC curves. gThe polymer was not isolated because of the low functionalization degree. a
whole thiols with electron withdrawing group are more labile, roughly in the order of N-acetyl-L-cysteine ≈ 3-mercaptopropanoic acid > 3-(trimethoxysilyl)propane-1-thiol > methyl 3-mercaptopropionate > 1-thioglycerol > β-mercaptoethanol > phenylmethanethiol ≈ (4-methoxyphenyl)methanethiol ≫ cysteamine. The amino functionalized thiol cysteamine is so inert that after irradiation for 3 days at elevated UV light intensity less than 10% of the terminal double bonds were converted. GPC analysis for PMHD functionalized with nonhydroxyl-containing thiols showed that the molecular weight increased accordingly while the molecular weight distributions remained in the range of 1.2−1.4 as in the case of 3(trimethoxysilyl)propane-1-thiol functionalized PMHD. The change in polarity after installations of various functional
of the silanols, which implies its potential as compatibilizer in the tire industry.19 As radical thiol−ene reaction is tolerant to a wide array of functionalities, thus various thiols were attempted to verify the feasibility of the approach (vide supra). As summarized in Table 3 (entries 2−10), PMHD was almost quantitatively functionalized in all cases, evidenced by the disappearance of peak (at about 5.8 ppm) corresponding to pendant vinyl group and emergence of new set of peaks corresponding to the installed functional group in the 1H NMR spectra (Figures S11−18, Supporting Information). At constant ultraviolet light irradiation intensity, different thiols require different reaction times to achieve full conversion, confirming the influence of thiol structure on the reactivity as reported previously.10a,20 On the E
DOI: 10.1021/acs.macromol.5b02654 Macromolecules XXXX, XXX, XXX−XXX
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Figure 5. 1H NMR (25 °C, CDCl3) spectrum of 3-(trimethoxysilyl)propane-1-thiol functionalized PMHD (asterisk denotes residual solvents in the polymer) (Table 3, entry 1). The residual 3,4-structures were not marked for clarity.
Table 4. Postmodification of Poly(MHD-ran-IP) with 3(Trimethoxysilyl)propane-1-thiola entry
MHD contb (%)
time (min)
FDc (%)
Mn,GPC (×10−4)d
PDId
Tge (°C)
1 2 3 4f 5g
90 70 50 30 10
120 90 60 40 25
100 100 100 100 100
10.91 9.03 7.29 5.87 4.72
1.31 1.27 1.35 1.38 1.42
−77.9 −76.3 −74.1 −70.6 −64.7
a
Conditions: 1.5 mg of photoinitiator DMPA, 60 mg of copolymer, thiol (5 mol equiv of monomer units), 5 mL of THF, T = 25 °C, UV light intensity (1.42 mW/cm2). bMHD content in the copolymer. c Functionalization degrees (%) of the pendent double bond established by 1H NMR spectra. dDetermined by GPC in THF using polystyrene as standard. eGlass transition temperature (Tg) determined by DSC (heating rate: 10 °C min−1, second scan). f1 mg of photoinitiator DMPA, thiol (7.5 mol equiv of monomer units), 7 mL of THF, UV light intensity (0.95 mW/cm2). g3 mL of DMPA solution in THF (0.1 mg/mL), thiol (10 mol equiv of monomer units), 6 mL of THF, UV light intensity (0.48 mW/cm2).
Figure 6. GPC traces for PMHD before and after postfunctionalization of 3-(trimethoxysilyl)propane-1-thiol.
groups was conspicuously manifested in the solubility of the resulting materials that 3-(trimethoxysilyl)propane-1-thiol, phenylmethanethiol, or (4-methoxyphenyl)methanethiol functionalized PMHD were readily dissolved in toluene, while methyl 3-mercaptopropionate or β-mercaptoethanol functionalized polymers were scarcely soluble in THF and the 1thioglycerol, 3-mercaptopropanoic acid, or N-acetyl-L-cysteine functionalized polymers were only soluble in dimethyl sulfoxide. The relative polarity of these highly cis-1,4-regulated functional 1,3-butadiene derivatives was also confirmed by the characterization of the static water contact angle (WCA) of them, measured using the sessile drop method (Table 4 and Figure S20). The results showed that phenylmethanethiol and (4-methoxyphenyl)methanethiol functionalized PMHD were hydrophobic with WCA of 98.5° and 90.5°, respectively. PMHD carrying 3-(trimethoxysilyl)propane-1-thiol (85.1°), β-
mercaptoethanol (81.7°), methyl 3-mercaptopropionate (78.1°), and 1-thioglycerol (70.2°) were becoming increasingly hydrophilic. Interestingly, WCA of the carboxylic acid group containing functionalized PMHD (3-mercaptopropanoic acid and N-acetyl-L-cysteine) were drastically reduced, making them highly hydrophilic diene-based materials. These polar hydroxyl, ester, or carboxylic acid functional groups will endow the resulting diene-based materials with improved compatibility with other polymers and organic and inorganic fillers. As model homopolymers of various functional diene-based polymers, these new materials also display intriguingly versatile thermal properties, shedding light on the influence of various F
DOI: 10.1021/acs.macromol.5b02654 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Scheme 1. Postmodification of PMHD with Various Thiol Compoundsa
a
The residual 3,4-structures were not marked for clarity.
Rigid benzene ring containing functionalities including phenyl and 4-methoxyphenyl groups constrain the backbone bond rotation, thus modestly raising the Tg values to −41.6 and −30.3 °C, respectively (Table 3, entries 7 and 8). For hydroxyl containing polymers such as β-mercaptoethanol and 1thioglycerol functionalized PMHD both polarity and hydrogen bonding play roles in determining thermal transition temperatures. It is interesting to note that the monohydric alcohol or carboxylic acid functionalized polymers are amorphous with glass transition temperatures of −43.1 and −32.3 °C, respectively, while the dihydric alcohol functionalized polymer is a semicrystalline material with Tm value of 50.1 °C, probably because of strong intermacromolecular hydrogen bonding making the polymer chain form ordered microdomains (Figure 7), as evidenced by the temperature-dependent FTIR analysis of the resulting polymer (Figure S10).21 We expected a higher melting temperature for N-acetyl-L-cysteine functionalized polymer as the amide group is known to form strong intermolecular hydrogen bonding.22 A rather high glass transition temperature of 45.1 °C was observed instead. The lack of crystalline domains may be attributed to the competitive hydrogen bonding of the carboxylic acid group and consequently unorderly formation of hydrogen bonds, as reported in the literature.23 Functionalization of copolymers of MHD and IP to obtain functionalized polybudiene materials, which makes more sense in practical manufacturing, is challenging, as in the presence of large excess of internal backbone double bonds they may compete with the pendant terminal ones, leading to loss of stereoregularity or other unexpected side reactions. Thus, the thiol−ene click reaction was carefully monitored by 1H NMR spectrum. With high MHD contents (≥50%) in the copolymer, the functionalization reaction went into completion smoothly, as evidenced by the complete disappearance of peak at 5.80 and 4.93 ppm (Figure S11). When the MHD content is no more than 30%, cross-linking sets in quickly (the functionalized copolymers in Table 4, entries 4 and 5, already became insoluble in THF after 60 and 30 min of irradiation, respectively). The feeding amount of 3-(trimethoxysilyl)-
Figure 7. Proposed mechanism of intermacromolecular hydrogen bonding in 1-thioglycerol functionalized PMHD.
Scheme 2. Two-Step Synthesis of MHD
polar groups on the thermal properties of functionalized polybutadienes. The slightly polar trimethoxysilyl or methyl ester groups increase the glass transition temperature a bit to −78.4 and −68.1 °C, respectively (Table 3, entries 1 and 5). G
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under a nitrogen atmosphere. The thermal history difference in the polymers was eliminated by first heating the specimen to 70 °C and cooling at 10 °C min−1 to −110 °C, and then a second heating from −110 to 70 °C at 10 °C min−1 was performed. The yttrium complex 1 was prepared according to the literature.13 Preparation of Monomer. The vinyl-functionalized butadiene monomer was synthesized via two steps as described above. 2-Bromol,5-hexadiene was prepared according to the literature.27 Vinylmagnesium bromide in THF (0.6 mol) was added dropwise to 2bromo-l,5-hexadiene (0.04 mol) catalyzed by [1,3-bis(diphenylphosphino)propane]dichloronickel (2 mmol) at 0 °C in an ice− water bath. After stirring for about 16 h at room temperature, the reaction mixture was hydrolyzed by adding saturated ammonium chloride solution and then extracted with diethyl ether three times. After careful evaporation of the solvent, the residue was distilled to give a colorless liquid of MHD at reduced pressure (boiling point 45 °C at 50 mmHg). Their spectroscopic properties (NMR) were identical to those reported in the literature.28 Homopolymerization of MHD. Under a nitrogen atmosphere, complex 1 (10.0 mg, 10.0 μmol) and borate (9.2 mg, 10.0 μmol) were placed into a 10.0 mL flask, and then 2.5 mL of toluene was added and stirred for about 5 min. MHD (0.27 g, 2.5 mmol) was subsequently added and vigorously stirred for 5 min. The viscous solution was poured into ethanol to give a sticky polymer that was dried under vacuum to a constant weight (0.27 g, 100%). 1H NMR (400 MHz, CDCl3, 25 °C): δ 5.79 (m, 1H, −CH2−CHCH2), 5.14 (t, 1H, −CH2−CHC(R)−CH2−), 4.98 (d, 1H, −CH2−CHCH2), 4.91 (d, 1H, −CH2−CHCH2), 4.78 (d, minor 1,4-regioselective peak), 2.13 (m, 2H, −CH2−), 2.09 (m, 2H, −CH2−). 13C NMR (100 MHz, CDCl3, 25 °C): δ 138.84 (−CH2−CHCH2), 138.70 (−CH2−CH C(R)−CH 2 −), 125.06 (−CH 2 −CHC(R)−CH 2 −), 114.46 (−CH2−CHCH2), 36.39 (−CH2−CHC(R)−CH2−), 32.70 (−CH 2 −CHCH 2 ), 30.75 (−CH 2 −CH 2 −CHCH 2 ), 26.88 (−CH2−CHC(R)−CH2−). Random Copolymerization of MHD and Isoprene. Under a nitrogen atmosphere, complex 1 (10.0 mg, 10.0 μmol) and borate (9.2 mg, 10.0 μmol) were placed into a 10.0 mL flask, and then 2.5 mL of toluene was added and stirred for about 5 min. MHD (0.27 g, 2.5 mmol) and isoprene (0.17 g, 2.5 mmol) in 2.5 mL of toluene were subsequently added and vigorously stirred for 20 min. The viscous solution was poured into ethanol to give a sticky polymer that was dried under vacuum to a constant weight (0.43 g, 98%). 1H NMR (400 MHz, CDCl3, 25 °C): δ 5.80 (m, 1H, −CH2−CHCH2), 5.15 (t, 2H, −CH2−CHC(R)−CH2−), 4.99 (d, 1H, −CH2−CH CH2), 4.93 (d, 1H, −CH2−CHCH2), 4.79 (d, minor 1,4regioselective peak), 4.70 (d, minor 1,4-regioselective peak), 2.14 (m, 2H, −CH2−), 2.05 (m, 10H, −CH2−), 1.69 (s, 3H, −CH2−CH C(CH3)−CH2−). 13C NMR (100 MHz, CDCl3, 25 °C): δ 138.88 (−CH2−CHCH2), 138.67 (−CH2−CHC(R)−CH2−), 135.33 (−CH 2 −CHC(CH 3 )−CH 2 −), 125.09 (−CH 2 −CHC(R)− CH2−), 114.44 (−CH2−CHCH2), 36.42 (−CH2−CHC(R)− CH2−), 32.72 (−CH2−CHCH2), 32.36 (−CH2−CHC(CH3)− CH2−), 30.75 (−CH2−CH2−CHCH2), 26.89 (−CH2−CH C(R)−CH 2 −), 26.49 (−CH 2 −CHC(CH 3 )−CH 2 −), 23.58 (−CH2−CHC(CH3)−CH2−). Block Copolymerization of MHD and Isoprene. Under a nitrogen atmosphere, complex 1 (10.0 mg, 10.0 μmol) and borate (9.2 mg, 10.0 μmol) were placed into a 10.0 mL flask, and then 5.0 mL of toluene was added and stirred for about 5 min. MHD (0.27 g, 2.5 mmol) was first added and vigorously stirred for 20 min. Then isoprene (0.17 g, 2.5 mmol) was added and stirred for another 20 min. The viscous solution was poured into ethanol to give a sticky polymer that was dried under vacuum to a constant weight (0.41 g, 93%). The 1 H NMR spectrum of poly(MHD-b-IP) is identical to that of poly(MHD-ran-IP). 13C NMR (100 MHz, CDCl3, 25 °C): δ 138.85 (−CH2−CHCH2), 138.71 (−CH2−CHC(R)−CH2−), 135.35 (−CH2−CHC(CH3)−CH2−), 125.18 (−CH2−CHC(CH3)− CH2−), 125.06 (−CH2−CHC(R)−CH2−), 114.46 (−CH2− CHCH2), 36.40 (−CH2−CHC(R)−CH2−), 32.70 (−CH2− CHCH2), 32.35 (−CH2−CHC(CH3)−CH2−), 30.75 (−CH2−
propane-1-thiol was raised while the ultraviolet light intensity and initial concentrations of photoinitiator was reduced accordingly, to slow the reaction rate and eliminate the occurrence of side reactions. 24 The copolymers were successfully fully functionalized, affording functional polybutadiene derivatives with monomodal molecular weight distribution. DSC analysis of the resulting functional materials reveals that with decreasing content of pendant trimethoxysilyl group, glass transition temperatures increases in the range of Tgs of homopolymers of trimethoxysilyl-functionalized butadiene (−78.4 °C) and polyisoprene (−64.0 °C), as expected for the random copolymers of these two monomers.
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CONCLUSION In summary, the terminal-vinyl functionalized butadiene derivative 3-methylenehepta-1,6-diene (MHD) was polymerized for the first time, affording a rubber-like material in a living and highly cis-1,4-selective (98.5%) mode, evidenced by NMR spectrum analysis of the resulting polymer. As every chain unit of PMHD contains one terminal carbon−carbon double bond, it can be completely converted into homopolymers of various functional butadiene derivatives through thiol−ene click reactions with a wide array of thiols containing trimethoxysilyl, hydroxyl, ester, or carboxylic acid functionalities, while at the same time the main chain cis-1,4-macrostructures remain intact. This new monomer also form block or random copolymers with isoprene; thus, cis-1,4 butadiene-based polymers with various incorporated functionality ratios can be obtained by tuning the monomer feeding ratio and subsequently clicking the obtained copolymer with thiol. In comparison with their parent polymer PMHD, functionalized butadiene-based materials displayed enhanced hydrophilicity, evidenced by decreased water contact angles. Moreover, these model homopolymers of various functional butadiene derivatives also display versatile glass transition temperatures. This strategy provides a new approach for preparing well-defined functional diene-based polymers possessing high stereotacticity. Further work is underway to reduce the functionality ratio in the copolymers to 5% or lower to investigate the compatibility of these functionalized diene-based elastomer with silica.
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EXPERIMENTAL SECTION
General Methods. All operations were carried out under an atmosphere of argon using standard Schlenk techniques or in a nitrogen gas filled MBraun glovebox. Solvents were reagent grade, dried by standard methods,25 and distilled under nitrogen prior to use. Toluene and THF were dried over Na. [Ph3C][B(C6F5)4] was prepared according to the published procedures.26 Deuterated NMR solvents were purchased from Cambridge Isotopes, dried over Na (for C6D6) and molecular sieve (for CDCl3), and stored in the glovebox. 2,3-Dibromopropene and [1,3-bis(diphenylphosphino)propane]-dichloronickel was purchased from Aladdin. 2,2-Dimethoxy-2-phenylacetophenone (DMPA), cysteamine, and (4-methoxyphenyl)methanethiol were purchased from Aldrich and used without further purification. 3-(Trimethoxysilyl)propane-1-thiol, β-mercaptoethanol, 1-thioglycerol, 3-mercaptopropanoic acid, methyl 3-mercaptopropionate, N-acetyl-L-cysteine, and phenylmethanethiol were purchased from TCI and used as received. Glassware and vials used in the polymerization were dried in an oven at 115 °C overnight and undergone the vacuum−argon cycle three times. 1H and 13C NMR spectra were recorded on a Bruker AV400 spectrometer. The molecular weight and molecular weight distribution of the polymers were measured by a TOSOH HLC 8220 GPC at 40 °C using THF as eluent (the flow rate was 0.35 mL/min) against polystyrene standards. DSC was performed on a Mettler TOPEM TM DSC instrument H
DOI: 10.1021/acs.macromol.5b02654 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules CH 2 −CHCH 2 ), 26.88 (−CH 2 −CHC(R)−CH 2 −), 26.54 (−CH2−CHC(CH3)−CH2−), 23.57 (−CH2−CHC(CH3)− CH2−). General Procedures for Thiol−Ene Reactions. In a 10 mL vial, 60 mg of polymer was dissolved in THF at room temperature. After the addition of thiol (5 mol equiv of pendent double bonds) and 2 mg of 2,2-dimethoxy-2-phenylacetophenone (DMPA), the mixture was purged with argon for 10 min. The thiol−ene reaction was performed under UV light (365 nm) for specified time intervals without stirring at room temperature. The resulting polymer was purified by precipitation in specific solvent and washing with methanol three times. It was then dried under vacuum to a constant weight. PMHD + 3-(Trimethoxysilyl)propane-1-thiol Adduct. The product was precipitated into methanol to yield a sticky material. 1H NMR (400 MHz, CDCl3, 25 °C): δ 5.13 (br s, 1H, −CH2−CH C(R)−CH2−), 3.55 (s, 9H, Si(OMe)3), 2.49 (m, 4H, −CH2−S− CH2−), 2.01 (m, 6H, −CH2−CHC(−CH2−R)−CH2−), 1.68 (m, 2H, −S−CH2−CH2−CH2−Si(OMe)3), 1.46−1.55 (m, 4H, −CH2− CH2−CH2−CH2−S−), 0.74 (t, 2H, −CH2−Si(OMe)3). PMHD + β-Mercaptoethanol Adduct. The product was precipitated into water to yield a sticky material. 1H NMR (400 MHz, DMSO-d6, 25 °C): δ 5.08 (br s, 1H, −CH2−CHC(R)− CH2−), 4.70 (t, 1H, −CH2OH), 3.49 (q, 2H, −CH2OH), 2.52 (m, 4H, −CH2−S−CH2−), 1.94−1.98 (m, 6H, −CH2−CHC(−CH2− R)−CH2−), 1.40−1.47 (m, 4H, −CH2−CH2−CH2−CH2−S−). PMHD + 1-Thioglycerol Adduct. The product was precipitated into water to yield a sticky material. 1H NMR (400 MHz, DMSO-d6, 25 °C): δ 5.09 (br s, 1H, −CH2−CHC(R)−CH2−), 4.69 (s, 1H, −CH2OH), 4.52 (s, 1H, −CH(OH)−CH2OH), 3.53 (m, 1H, −CH(OH)−CH2OH), 3.34 (m, 2H, −CH(OH)−CH2OH), 2.57 (m, 2H, −CH2−CH2−S−CH2−), 2.42 (m, 2H, −CH2−CH2−S− CH2−), 1.94−1.98 (m, 6H, −CH2−CHC(−CH2−R)−CH2−), 1.40−1.48 (m, 4H, −CH2−CH2−CH2−CH2−S−). PMHD + 3-Mercaptopropanoic Acid Adduct. The product was precipitated into water to yield a sticky material. 1H NMR (400 MHz, CDCl3, 25 °C): δ 5.20 (br s, 1H, −CH2−CHC(R)−CH2−), 2.76 (t, 2H, −CH2−COOH), 2.05−2.60 (m, 4H, −CH2−S−CH2−), 2.05− 2.11 (m, 6H, −CH2−CHC(−CH2−R)−CH2−), 1.53−1.60 (m, 4H, −CH2−CH2−CH2−CH2−S−). PMHD + Methyl 3-Mercaptopropionate Adduct. The product was precipitated into methanol to yield a sticky material. 1H NMR (400 MHz, CD3OD, 25 °C): δ 5.14 (br s, 1H, −CH2−CHC(R)− CH2−), 3.69 (s, 3H, −COOMe), 2.77 (t, 2H, −CH2−COOMe), 2.61 (t, 2H, −CH2−S−CH2−CH2−COOMe), 2.54 (t, 2H, −CH2−S− CH2−CH2−COOMe), 2.02 (m, 6H, −CH2−CHC(−CH2−R)− CH2−), 1.47−1.56 (m, 4H, −CH2−CH2−CH2−CH2−S−). PMHD + N-Acetyl-L-cysteine Adduct. The product was precipitated into water to yield a white powder. 1H NMR (400 MHz, DMSO-d6, 25 °C): δ 5.06 (br s, 1H, −CH2−CHC(R)− CH2−), 4.35 (br s, 1H, −CH(COOH)−NH−), 2.83 (m, 1H, −S− CH2−CH(COOH)−), 2.69 (m, 1H, −S−CH2−CH(COOH)−), 2.50 (br s, 2H, −CH2−S−CH2−CH(COOH)−), 1.92−1.96 (m, 6H, −CH2−CHC(−CH2−R)−CH2−), 1.85 (s, 3H, −CO−CH3), 1.38−1.44 (m, 4H, −CH2−CH2−CH2−CH2−S−). PMHD + Phenylmethanethiol Adduct. The product was precipitated into methanol to yield a sticky material. 1H NMR (400 MHz, CDCl3, 25 °C): δ 7.27 (br s, 4H, −PhH), 7.21 (br s, 1H, −PhH), 5.08 (br s, 1H, −CH2−CHC(R)−CH2−), 3.66 (s, 2H, −S−CH2−Ph), 2.39 (br s, 2H, −CH2−S−CH2−Ph), 1.99 (m, 6H, −CH2−CHC(−CH2−R)−CH2−), 1.42−1.52 (m, 4H, −CH2− CH2−CH2−CH2−S−). PMHD + (4-Methoxyphenyl)methanethiol Adduct. The product was precipitated into methanol to yield a sticky material. 1H NMR (400 MHz, CDCl3, 25 °C): δ 7.18 (d, 2H, −PhH), 6.80 (d, 2H, −PhH), 5.09 (br s, 1H, −CH2−CHC(R)−CH2−), 3.75 (s, 3H, −PhOMe), 3.62 (s, 2H, −S−CH2−PhOMe), 2.38 (br s, 2H, −CH2− S−CH2−PhOMe), 1.99 (m, 6H, −CH 2−CHC(−CH 2−R)− CH2−), 1.42−1.52 (m, 4H, −CH2−CH2−CH2−CH2−S−). Poly(MHD-ran-IP) + 3-(Trimethoxysilyl)propane-1-thiol Adduct. The product was precipitated into methanol to yield a sticky
material. 1H NMR (400 MHz, CDCl3, 25 °C): δ 5.12 (br s, −CH2− CHC(R)−CH2−), 3.56 (s, Si(OMe)3), 2.50 (m, −CH2−S−CH2−), 1.99−2.03 (m, 6H, −CH2−CHC(−CH2−R)−CH2−), 1.68 (m, −S−CH 2 −CH 2 −CH 2 −Si(OMe) 3 and −CH 2 −CHC(CH 3 )− CH2−), 1.60 (br s, −CH2−CHC(CH3)−CH2−), 1.47−1.56 (m, −CH2−CH2−CH2−CH2−S−), 0.75 (t, −CH2−Si(OMe)3).
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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.5b02654. 1 H NMR and 13C NMR spectra of random or block copolymers of MHD and isoprene in Table 2; DSC curves of PMHD (Table 1), random or block copolymers of MHD and isoprene (Table 2), and functionalized PMHD (Table 3); 1H NMR spectra of functionalized PMHD (Table 3) and copolymer with various trimethoxysilyl functionality ratios (Table 4); water contact angles of PMHD and functionalized PMHD in Table 3 (PDF)
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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 was partially supported by MST for “973” project No. 2015CB654702 and the NSFC for projects Nos. 2136114037, 21374112, and 21304088.
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REFERENCES
(1) Akelah, A.; Moet, A. Functionalized Polymers and Their Applications; Chapman and Hall: New York, 1990. (2) (a) Payne, A. R. J. Appl. Polym. Sci. 1962, 6, 57. (b) Payne, A. R. J. Appl. Polym. Sci. 1962, 6, 368. (3) (a) Romulus, J.; Henssler, J. T.; Weck, M. Macromolecules 2014, 47, 5437. (b) Gauthier, M. A.; Gibson, M. I.; Klok, H. A. Angew. Chem., Int. Ed. 2009, 48, 48. (4) (a) Jing, Y.; Sheares, V. V. Macromolecules 2000, 33, 6262. (b) Sheares, V. V.; Wu, L. F.; Li, Y. X.; Emmick, T. K. J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 4070. (c) Synthesis of Polymers−New Structures and Methods; Schluter, A. D., Hawker, C. J., Sakamoto, J., Eds.; Wiley: Weinheim, Germany, 2012. (d) Hirao, A.; Goseki, R.; Ishizone, T. Macromolecules 2014, 47, 1883. (5) (a) Hirao, A.; Nagawa, T.; Hatayama, T.; Yamaguchi, K.; Nakahama, S. Macromolecules 1985, 18, 2101. (b) Takenaka, K.; Hirao, A.; Hattori, T.; Nakahama, S. Macromolecules 1987, 20, 2034. (c) Takenaka, K.; Hattori, T.; Hirao, A.; Nakahama, S. Macromolecules 1989, 22, 1563. (d) Hirao, A.; Hiraishi, Y.; Nakahama, S. Macromolecules 1998, 31, 281. (e) Takenaka, K.; Kawamoto, S.; Miya, M.; Takeshita, H.; Shiomi, T. Polym. Int. 2010, 59, 891. (6) (a) Petzhold, C.; Stadler, R.; Frauenrath, H. Makromol. Chem., Rapid Commun. 1993, 14, 33. (b) Petzhold, C.; Morschhauser, R.; Kolshorn, H.; Stadler, R. Macromolecules 1994, 27, 3707. (c) Petzhold, C.; Stadler, R. Macromol. Chem. Phys. 1995, 196, 2625. (d) Mannebach, G.; Bieringer, R.; Morschhauser, R.; Stadler, R. Macromol. Symp. 1998, 132, 245. (7) (a) Jing, Y.; Sheares, V. V. Macromolecules 2000, 33, 6255. (b) Beery, M. D.; Rath, M. K.; Sheares, V. V. Macromolecules 2001, 34, 2469. (c) Wu, L. F.; Sheares, V. V. J. Polym. Sci., Part A: Polym. Chem. I
DOI: 10.1021/acs.macromol.5b02654 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules 2001, 39, 3227. (d) Yang, Y.; Lee, J.; Cho, M.; Sheares, V. V. Macromolecules 2006, 39, 8625. (8) (a) Chung, T. C.; Rhubright, D. Macromolecules 1991, 24, 970. (b) Chung, T. C.; Rhubright, D.; Jiang, G. J. Macromolecules 1993, 26, 3467. (c) Zou, J. F.; Cao, C. G.; Dong, J. Y.; Hu, Y. L.; Chung, T. C. Macromol. Rapid Commun. 2004, 25, 1797. (d) Zhang, M.; Colby, R. H.; Milner, S. T.; Chung, T. C. Macromolecules 2013, 46, 4313. (e) Zhang, M.; Yuan, X. P.; Wang, L.; Chung, T. C. Macromolecules 2014, 47, 571. (9) (a) Chung, T. C.; Raate, M.; Berluche, E.; Schulz, D. N. Macromolecules 1988, 21, 1903. (b) Hou, S. J.; Chan, W. K. Macromolecules 2002, 35, 850. (c) Derouet, D.; Tran, Q. N.; Ha Thuc, H. Eur. Polym. J. 2007, 43, 1806. (d) Wurm, F.; LópezVillanueva, F.-J.; Frey, H. Macromol. Chem. Phys. 2008, 209, 675. (e) Justynska, J.; Schlaad, H. Macromol. Rapid Commun. 2004, 25, 1478. (f) Justynska, J.; Hordyjewicz, Z.; Schlaad, H. Polymer 2005, 46, 12057. (g) You, L. C.; Schlaad, H. J. Am. Chem. Soc. 2006, 128, 13336. (h) Geng, Y.; Discher, D. E.; Justynska, J.; Schlaad, H. Angew. Chem., Int. Ed. 2006, 45, 7578. (i) ten Brummelhuis, N.; Diehl, C.; Schlaad, H. Macromolecules 2008, 41, 9946. (j) Ameri David, R. L.; Kornfield, J. A. Macromolecules 2008, 41, 1151. (k) Xu, J. T.; Boyer, C. Macromolecules 2015, 48, 520. (l) Macit, H.; Hazer, B. Eur. Polym. J. 2007, 43, 3865. (m) Keleş, E.; Hazer, B.; Cömert, F. B. Mater. Sci. Eng., C 2013, 33, 1061. (n) Hazer, B. Polym. Degrad. Stab. 2015, 119, 159. (o) Wu, B.; Lenz, R. W.; Hazer, B. Macromolecules 1999, 32, 6856. (10) (a) Hoyle, C. E.; Bowman, C. N. Angew. Chem., Int. Ed. 2010, 49, 1540. (b) Hoyle, C. E.; Lowe, A. B.; Bowman, C. N. Chem. Soc. Rev. 2010, 39, 1355. (c) Lowe, A. B. Polym. Chem. 2014, 5, 4820. (d) Espeel, P.; Du Prez, F. E. Macromolecules 2015, 48, 2. (11) Nomura, K.; Liu, J.; Fujiki, M.; Takemoto, A. J. Am. Chem. Soc. 2007, 129, 14170. (12) (a) Wang, X. Y.; Wang, Y. X.; Li, Y. S.; Pan, L. Macromolecules 2015, 48, 1991. (b) Langston, J. A.; Colby, R. H.; Chung, T. C. M.; Shimizu, F.; Suzuki, T.; Aoki, M. Macromolecules 2007, 40, 2712. (c) Lin, W. T.; Shao, Z.; Dong, J. Y.; Chung, T. C. M. Macromolecules 2009, 42, 3750. (13) Wang, L.; Cui, D.; Hou, Z.; Li, W.; Li, Y. Organometallics 2011, 30, 760. (14) To compare the 13C NMR spectrum of cis-1,4- and trans-1,4PMHD, we synthesized trans-1,4-dominate PMHD utilizing a catalyst system previously reported by our group to generate trans-1,4dominate polyisoprene. See Supporting Information. (15) (a) Kobayashi, S.; Kataoka, H.; Ishizone, T. Macromolecules 2009, 42, 5017. (b) Takenaka, K.; Kawamoto, S.; Miya, M.; Takeshita, H.; Shiomi, T. Polym. Int. 2010, 59, 891. (16) Vanhoorne, P.; Dubois, P.; Jerome, R.; Teyssie, P. Macromolecules 1992, 25, 37. (17) (a) Klemm, E.; Gorski, U. Angew. Makromol. Chem. 1993, 207, 187. (b) Romani, F.; Passaglia, E.; Aglietto, M.; Ruggeri, G. Macromol. Chem. Phys. 1999, 200, 524. (c) Roper, T. M.; Guymon, C. A.; Jönsson, E. S.; Hoyle, C. E. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 6283. (18) Nystrom, D.; Antoni, P.; Malmstrom, E.; Johansson, M.; Whittaker, M.; Hult, A. Macromol. Rapid Commun. 2005, 26, 524. (19) (a) Schapman, F.; Couvercelle, J. P.; Bunel, C. Polymer 1998, 39, 4955. (b) Sandstrom, P. H.; Verthe, J. J. A.; Dirossi, R. R.; Gross, B. B. EP 1484362, The Goodyear Tire & Rubber Company: USA, invs., 2004. (c) Luo, S.; Nakagawa, R.; Poulton, J. T.; Suzuki, E.; Yan, Y. Y. US 2007149717, Bridgestone Americas Holding, Inc.: USA, invs., 2007. (20) Hong, M.; Liu, S. R.; Li, B. X.; Li, Y. S. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 2499. (21) At 25 °C the temperature-dependent FTIR spectra show bands at 3365 cm−1, assigned to the O−H stretching, close to the stretching of hydrogen-bonded O−H groups in poly(vinyl alcohol) (at about 3340 cm−1; Adv. Polym. Sci. 1960, 2, 51−172). As the temperature gradually changes from 25 to 90 °C, the bands at 3365 cm−1 move to 3402 cm−1. The intensity and the width of the bands at 3365 cm−1
decrease and narrow upon heating, indicating the dissociation of hydrogen bonds (also see literature: RSC Adv. 2015, 5, 84729). (22) Scavuzzo, J.; Tomita, S.; Cheng, S.; Liu, H.; Gao, M.; Kennedy, J. P.; Sakurai, S.; Cheng, S. Z. D.; Jia, L. Macromolecules 2015, 48, 1077. (23) Lotti, L.; Coiai, S.; Ciardelli, F.; Galimberti, M.; Passaglia, E. Macromol. Chem. Phys. 2009, 210, 1471. (24) Derboven, P.; D’hooge, D. R.; Stamenovic, M. M.; Espeel, P.; Marin, G. B.; Du Prez, F. E.; Reyniers, M. F. Macromolecules 2013, 46, 1732. (25) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chemicals, 2nd ed.; Pergamon: Oxford, England, 1980. (26) Chein, J. C.W.; Tsai, W.-M.; Rausch, M. D. J. Am. Chem. Soc. 1991, 113, 8570. (27) Peterson, P. E.; Nelson, D. J.; Risener, R. J. Org. Chem. 1986, 51, 2381. (28) Kawamura, T.; Matsunaga, M.; Yonezawa, T. J. Am. Chem. Soc. 1978, 100, 92.
J
DOI: 10.1021/acs.macromol.5b02654 Macromolecules XXXX, XXX, XXX−XXX
