Regioselective Ring-Opening Metathesis Polymerization of 3

Mar 16, 2016 - Allyl-substituted cyclooctenes with ether side-chains [methoxy, methoxy-terminated oligo(ethylene glycol)s, and tetrahydrofurfuryloxy g...
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Regioselective Ring-Opening Metathesis Polymerization of 3‑Substituted Cyclooctenes with Ether Side Chains. Shingo Kobayashi,*,† Kousaku Fukuda,‡ Maiko Kataoka,‡ and Masaru Tanaka*,† †

Institute for Materials Chemistry and Engineering, Kyushu University, CE41 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Department of Biochemical Engineering, Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan

‡

S Supporting Information *

ABSTRACT: Allyl-substituted cyclooctenes with ether sidechains [methoxy, methoxy-terminated oligo(ethylene glycol)s, and tetrahydrofurfuryloxy group] were prepared as monomers and polymerized by ring-opening metathesis polymerization (ROMP) using Grubbs second-generation catalyst. In all cases, the ROMP of allyl-substituted monomers proceeded in a regio- and stereoselective manner to afford polymers with remarkably high head-to-tail regioregularity with high transstereoregularity. The regio- and stereoregularity of polymers were affected by the bulkiness of the substituent, and the ROMP of tetrahydrofurfuryloxy-substituted cyclooctene exhibited nearly perfect regio- (head-to-tail = 99%) and stereoselectivity (transdouble bond = 99%). Chemical hydrogenation of obtained polymers afforded model poly(ethylene-co-vinyl ether)s with precisely placed ether branches on every eighth backbone carbon. Differential scanning calorimetry (DSC) was used to study the thermal properties, and the hydrophilicity of polymers was evaluated by water contact angle measurement. The surface hydrophilicity of unsaturated polymers was effectively tuned by changing the side-chain length of oligo(ethylene glycol) groups while maintaining the hydrophobic character unchanged for saturated versions.

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INTRODUCTION Polyethylene (PE) is one of the most chemically stable and inert polymeric materials with the simplest structure: a hydrocarbon with a long chain entirely consisting of only hydrogen and carbon.1 The chemical stability and inertness of PE are due to the absence of heteroatoms (e.g., oxygen, nitrogen, and phosphorus). The lack of polar functional groups containing heteroatoms impedes PE application in many areas that require good adhesion, coating, and compatibility characteristics.2 Thus, functionalization of PE has been extensively studied for the purpose of expanding its potential. A number of synthetic routes to functionalized PE have been developed to overcome the inevitable drawback.3−7 The most obvious synthetic pathway to functionalized PE is copolymerization of ethylene with polar vinyl monomers; however, the methodology always suffers from the extreme difference in reactivity between ethylene and other vinyl monomers.8 Linear ethylene/vinyl ether (EVE) copolymer is one of the most challenging targets in the synthesis of functionalized PE. When chain-growth polymerization is utilized, the polymer is considered to be inaccessible owing to the inherent reactivity difference of two monomers, ethylene and vinyl ether. The linear EVE copolymer is infeasible for conventional vinyl polymerizations and has never been made; however because Wagener et al. reported the first examples of linear EVE copolymers synthesized by a unique methodology, acyclic diene metathesis (ADMET) polymerization−hydrogenation pathway,9,10 olefin metathesis polymerization11−13 has emerged as an alternative approach to achieve model linear EVE © XXXX American Chemical Society

copolymers in which polyethylenes have ether side-chains. At the same time, the ADMET methodology has allowed manipulation of a primary polymer structure, side-chain branch placement along the polymer backbone.14 By using α,ω-dienes with a symmetric structure as a monomer, the ADMET methodology exclusively produces structurally unique polymers with precisely/regularly spaced side-chain branchesnamely, precision polyolefins.15−18 An alternative route to access EVE copolymers by utilizing olefin metathesis polymerization existsthat is, ring-opening metathesis polymerization (ROMP)−hydrogenation pathway.19−22 However, unlike the ADMET methodology, there are still very few reports describing the synthesis of precision polyolefins by utilizing the ROMP−hydrogenation methodology. Recently, Hillmyer et al. reported a series of papers describing the synthesis of polymers with extremely high regio- and stereoregularities from the ROMP of 3-substituted cyclooctenes using Grubbs second- (G2) and third-generation (G3) catalysts, and the polymers with precisely placed sidechain branches on every eighth backbone carbon were also achieved via the ROMP-hydrogenation pathway.23−27 Extensive research has been performed on the regio-/stereoselective ROMP of 3-substituted cycloalkenamerse.g., alkyl, phenyl, acetoxy, and a variety of polar functional groupsand details of the mechanism have gradually revealed that the high regio-/ Received: February 4, 2016 Revised: March 9, 2016

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DOI: 10.1021/acs.macromol.6b00273 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

Scheme 1. Synthesis of Precision EVE Copolymer via Regioselective ROMP of 3-Alkoxy-Substituted Cyclooctene, Followed by Hydrogenation

four consecutive columns [Tosho TSK-GELs (bead size, exclusionlimited molecular weight): G4000HXL (5 μm, 4 × 105), G3000HXL (5 μm, 6 × 104), G2000HXL (5 μm, 1 × 104), 30 cm each] and a guard column (TSK-guard column HXL-L, 4 cm). The system was operated at a flow rate of 1.0 mL/min using tetrahydrofuran (THF) as the eluent. Polystyrene standards were employed for calibration. Differential scanning calorimetry (DSC) measurement was performed on a Seiko Instruments Inc. X-DSC7000 with N2 as the purge gas at a rate of 5.0 °C/min from −100 to +50 °C. Water contact angle measurement was performed on an Erma G-1-1000 with the sessile drop method (2 μL of water droplet). The polymer-coated substrate for the measurement was prepared by spin-coating onto a 14 mm ϕ PET substrate, 0.2 w/v % polymer in THF solution was prepared, and the solution was coated twice on the substrate using a Mikasa spin coater MS-A100 at rates of 500 rpm for 5 s, 2000 rpm for 10 s, slope for 5 s, 4000 rpm for 5 s, and slope for 4 s and then dried. Monomer Synthesis. The synthesis of allyl-substituted cyclooctenes with an ether side-chain was performed according to a modified procedure from the literature.23 Detailed NMR structural assignments and NMR spectra of products are shown in the Supporting Information. 3-Methoxy-Z-cyclooct-1-ene (M): A mixture of 3-bromo-cyclooctene (42.6 g, 225 mmol) and 200 mL of methanol was stirred at 50 °C for 2 h. The excess methanol was removed under reduced pressure, and the crude product was purified by fractional vacuum distillation from CaH2-afforded 3-methoxy-Z-cyclooct-1-ene (18.2 g, 130 mmol, 58% yield, bp =50−52 °C at 70−80 Torr) as a colorless liquid (for details, see Supporting Information, page S02 and Figures S1−S5). 1 H NMR δ (ppm): 1.30−1.65 (m, 7H), 1.85−1.91 (ddt, 1H, J = 4.3, 9.0, and 13.2 Hz), 2.22−2.05 (m, 2H), 3.32 (s, 3H), 4.14 (dddd, 1H, J = 1.5, 4.5, 6.6, and 11.5 Hz), 5.47 (ddd, 1H, J = 1.5, 7.1, and 10.9 Hz), 5.71 (dddd, 1H, J = 1.6, 7.3, 9. 0, and 10.9 Hz). 13 C NMR δ (ppm): 23.74, 26.33, 26.55, 29.22, 35.72, 56.49, 78.29, 130.39, 133.79. ESI−MS: m/z calcd, 140.1201; found, 140.1302. Anal. Calcd for C9H16O: C, 77.1; H, 11.4; O, 11.4. Found: C, 77.3; H, 11.4; O, 10.3. 3-(2-Methoxyethoxy)-Z-cyclooct-1-ene (ME): In a 300 mL 3-neck round-bottom flask equipped with a magnetic stirrer, a reflux condenser, and an N2 gas inlet, the mixture of 3-bromo-cyclooctene (48.4 g, 255 mmol) and 2-methoxyethanol (200 mL) was stirred for 16 h at 50 °C and then 3 h at 100 °C under N2 gas purging through the reaction mixture to remove the byproduct 1,3-cyclooctadiene. The reaction mixture was poured into water and was extracted by diethyl ether three times. The organic layer was dried over anhydrous MgSO4. After concentration of the solution, the resulting crude product was purified by fractional vacuum distillation from CaH2-afforded 3-(2methoxyethoxy)-Z-cyclooct-1-ene (12.2 g, 66.3 mmol, 26% yield, bp =46−48 °C at 0.08−0.12 Torr) as a colorless liquid (for details, see Supporting Information, page S08 and Figures S6−S10). 1 H NMR δ (ppm): 1.27−1.70 (m, 5H), 1.88−1.99 (m, 1H), 2.10− 2.10 (m, 2H), 3.37 (s, 3H), 3.48−3.52 (m, 3H), 3.73−3.80 (m, 1H), 4.18−4.32 (m, 1H), 5.49 (ddd, 1H, J = 1.5, 7.3, and 10.8 Hz), 5.68 (dddd, 1H, J = 1.5, 7.3, 9.0, and 10.8 Hz). 13 C NMR δ (ppm): 23.76, 26.32, 26.55, 29.24, 35.80, 59.10, 68.00, 72.25, 77.18, 130.18, 133.93. ESI−MS: m/z calcd, 184.1463; found, 184.1843. Anal. Calcd for C11H20O2: C, 71.7; H, 10.9; O, 17.4. Found: C, 70.7; H, 10.8; O, 18.5.

stereoregularity of the regioselective ROMP-produced polymer originated from the steric repulsion between the N-heterocyclic carbene ligand on the metathesis catalysts and the substituent on the allyl position of the monomer.28,29 The energetically favorable distal-E monomer orientation leads to an intermediate with a substituent positioned γ to the ruthenium. The preferred reaction path provides polymers with a high degree of head-to-tail regioregularity.27 A number of studies have been performed to broaden the scope of functional groups that can be incorporated by regioselective ROMP; however, there is still plenty of room to improve the regioselectivity of the ROMP of 3-alkoxy substituted cyclooctenes. In this study, we investigated the regio- and stereoregularity of the polymers from 3-alkoxy-substituted cyclooctenes by utilizing the regioselective ROMP with G2 (Scheme 1). A series of methoxy (M), methoxy-terminated oligo(ethylene glycol) [monoethylene glycol (ME), di- (ME2), and tri(ME3)], and tetrahydrofurfuryl (T) side-chains were examined to ascertain the substituent effectiveness to improve the regioregularity. The resulting polymers were converted to their hydrogenated variants by chemical hydrogenation. They represent a class of precision polyolefins in which linear EVE copolymers with the alkoxy side-chain are located on every eighth backbone carbon as shown in Scheme 1. The thermal properties and hydrophilicity/hydrophobicity of the obtained polymers were also investigated to verify the effectiveness of the ROMP-hydrogenation methodology on the fine-tuning of EVE copolymer properties.

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EXPERIMENTAL SECTION

Materials. 3-Bromo-1-cyclooctene was prepared according to the literature procedure.27 Cyclooctene, 2-methoxyethanol, diethylene glycol monomethyl ether, and tributyl amine were purchased from Tokyo Chemical Industry Co., Ltd., Japan. Triethylene glycol monomethyl ether, tetrahydrofurfuryl alcohol, Grubbs secondgeneration catalyst {G2: [1,3-bis(2,4,6-trimethylphenyl)-2imidazolidinylidene]dichloro (phenylmethylene) (tricyclohexylphosphine)ruthenium(II)}, ethyl vinyl ether, and ptoluenesulfonyl hydrazide were purchased from Aldrich. The metal scavenger SiliaMetS DMT was purchased from Silicycle Inc. The chain transfer agent cis-4-octene (97%) was purchased from Alfa Aesar. Chloroform for polymerization was purchased from Kanto Chemical and was dried over molecular sieves (4A) prior to polymerization. Other commercially available reagents were used as received unless otherwise stated. Measurements. 1H and 13C NMR spectra were recorded on a JEOL ECX 500 MHz at room temperature. CDCl3 was used as a solvent. Proton chemical shifts were referenced to TMS (0.00 ppm). Carbon chemical shifts were referenced to CDCl3 (77.1 ppm). Electrospray ionization mass spectrometry (ESI−MS) data were collected on a JEOL LMS-T100LC instrument operated in the positive mode. Elemental analysis data were collected on a PerkinElmer CHNS/O 2400II Analyzer. The molecular weight (Mn(SEC)) and molecular weight distribution (Mw/Mn) of polymers were determined by a size exclusion chromatography (SEC) instrument on a Tosoh HPLC HLC-8220 system equipped with a refractive index and ultraviolet detectors at 40 °C. The column set of SEC was as follows: B

DOI: 10.1021/acs.macromol.6b00273 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 1. Polymers from the ROMP of Allyl-Substituted Monomers with Ether Side Chains Using G2a,b,c Mn (kg mol−1) d

entry

monomer

M/G2

M/CTA

convn (%)

yield (%)

calcd

1 2 3 4 5 6 7 8

M ME ME2 ME2 ME3 ME3 T T

2500 2500 2500 1000 2500 625 2500 1000

217 217 217 250 217 294 217 250

94 94 74 78 37 95 67 > 99

77 45 58 51 27 91 41 88

26 34 34 36 20 51 28 42

e

NMRf

SECg

Mw/Mng

transd,h (%)

HTd,i (%)

42 37 42 39 49 43 58 56

50 83 91 46 36 77 68 73

1.6 1.3 2.7 2.4 2.8 2.7 1.4 2.0

94 95 97 98 98 98 >99 >99

93 95 97 97 98 97 99 99

a

cis-4-Octene and ethyl vinyl ether were used as the CTA and polymerization terminator, respectively. b[M]0/([CTA]0 + [G2]0) = 200. cAll polymerizations were carried out in CHCl3 at room temperature for 20 h. d1M. e2M. dDetermined by 1H NMR spectroscopy. eMn,calcd = (MW of monomer) × [M]0/[G2]0 × fractional conversion. fDetermined by end-group analysis via 1H NMR measurement. gDetermined by SEC using polystyrene standards in THF at 40 °C. htrans- double bond content. iHead-to-tail content. 13 C NMR δ (ppm): 23.74, 25.55, 25.66, 26.32, 26.54, 28.21, 28.35, 29.25, 35.76, 35.83, 68.32, 71.51, 71.67, 77.19, 77.24, 77.96, 78.22, 129.99, 130.07, 134.06. ESI−MS: m/z calcd, 210.1620; found, 210.1962. Anal. Calcd for C13H22O2: C, 74.2; H, 10.6; O, 15.2. Found: C, 75.5; H, 10.5; O, 14.0. General Polymerization Procedure. An example of the polymerization procedure is described for entry 8 in Table 1. A mixed solution of T (13.8 g, 65.3 mmol), cis-4-octene (29.3 mg, 261 μmol), and G2 (55.6 mg, 65.5 μmol) in dry chloroform (2.0 M, 32.6 mL total volume) was prepared under nitrogen atmosphere and was charged into a two-neck round-bottom flask. The mixed solution was degassed three times by freeze−pump−thaw cycles and refilled with nitrogen gas. The solution was then stirred at room temperature (23 °C) for 20 h. The reaction was quenched by adding ethyl vinyl ether (100 μL, 1.0 mmol) and stirred for 30 min. The reaction mixture was diluted by adding chloroform (∼20 mL), and the metal scavenger (3.8 g, ca. 2.4 mmol of dimercaptotriazine on silica, 40 equiv to G2) was added to remove the catalyst residue. After the mixture was stirred at 40 °C overnight, the metal scavenger was filtered off, and the filtrate was concentrated on a rotary evaporator. The crude product was dissolved in THF, and the polymer was precipitated by pouring the solution into a large excess amount of methanol. The precipitated polymer was isolated by decantation, and the collected polymer was purified by repeating precipitation three times. The collected product was freeze-dried overnight from its benzene solution to afford poly(2{[(2Z) -cyclooct-2-ene-1-yl]oxymethyl}tetrahydrofuran) (PT, 12.2 g, 89% yield) as a colorless, highly viscous liquid. The following is the complete list. Poly(3-methoxy-Z-cyclooct-1-ene) (PM; for details, see Supporting Information, page S32 and Figures S26−S30): 1 H NMR δ (ppm): 1.12−1.40 (m, 7H), 1.41−1.54 (m, 1H), 1.90− 1.98 (dt, 2H, J = 7.0 and 7.0 Hz), 3.12 (s, 3H), 3.29−3.36 (dt, 1H, J = 6.5 and 8.0 Hz), 5.07−5.16 (dd, 1H, J = 8.5 and 15.5 Hz), 5.42−5.53 (dt, 1H, J = 7.0 and 15.5 Hz). 13 C NMR (125 MHz, CDCl3): σ = 25.35, 29.20, 29.30, 32.25, 35.72, 55.80, 82.68, 130.58, 134.32. Anal. Calcd for C9H16O: C, 77.1; H, 11.4; O, 11.4. Found: C, 77.0; H, 11.5; O, 11.5. Poly[3-(2-methoxyethoxy)-Z-cyclooct-1-ene] (PME; for details, see Supporting Information, page S38 and Figures S31−S35). 1 H NMR δ (ppm): 1.23−1.46 (m, 7H), 1.67−1.72 (m, 1H), 2.01− 2.10 (dt, 2H, J = 7.0 and 7.5 Hz), 3.35−3.40 (m, 4H), 3.49−3.65 (m, 4H), 5.25 (dd, 1H, J = 8.3 and 15.5 Hz), 5.56 (dt, 1H, J = 6.7 and 15.5 Hz). 13 C NMR δ (ppm): 25.47, 29.25, 29.34, 32.30, 35.74, 59.10, 67.25, 72.25, 81.74, 130.90, 134.12. Anal. Calcd for C11H20O2: C, 71.7; H, 10.9; O, 17.4. Found: C, 71.5; H, 10.9; O, 17.6.

3-[2-(2-Methoxyethoxy)ethoxy]-Z-cyclooct-1-ene (ME2): The same procedure was followed as described for ME, using 3-bromocyclooctene (45.2 g, 238 mmol) and 2-(2-methoxyethoxy)ethanol (200 mL). The reaction mixture was stirred for 44 h at 80 °C. After purification, 3-[2-(2-methoxyethoxy)ethoxy]-Z-cyclooct-1-ene (17.2 g, 75.4 mmol, 32% yield, bp =85−87 °C at 0.08−0.12 Torr) was obtained as a colorless liquid (for details, see Supporting Information, page S14 and Figures S11−S15). 1 H NMR δ (ppm): 1.31−1.70 (m, 7H), 1.90−1.97 (m, 1H), 2.03− 2.21 (m, 2H), 3.38 (s, 3H), 3.51−3.58 (m, 3H), 3.62−3.71 (m, 5H), 4.25−4.32 (ddt, 1H, J = 2.2, 7.1, 11.0 Hz), 5.46−5.52 (ddd, 1H, J = 1.3, 7.2, 10.8 Hz), 5.68 (dddd, 1H, J = 1.6, 7.3, 9.0, and 10.8 Hz). 13 C NMR δ (ppm): 23.78, 26.33, 26.55, 29.25, 35.84, 59.09, 68.07, 70.57, 70.92, 72.04, 77.14, 130.11, 133.98. ESI−MS: m/z calcd, 228.1725; found, 228.2038. Anal. Calcd for C13H24O3: C, 68.4; H, 10.5; O, 21.1. Found: C, 68.6; H, 10.6; O, 20.8. 3-{2-[2-(2-Methoxyethoxy)ethoxy]ethoxy}-Z-cyclooct-1-ene (ME3): The same procedure was followed as described for ME, using 3-bromo-cyclooctene (10.0 g, 52.0 mmol) and 2-[2-(2methoxyethoxy)ethoxy]ethanol (40 mL). The reaction mixture was stirred for 24 h at 50 °C and then 28 h at 80 °C. After purification, 3{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}-Z-cyclooct-1-ene (2.08 g, 7.65 mmol, 15% yield, bp =100−102 °C at 0.08−0.12 Torr) was obtained as a colorless liquid (for details, see Supporting Information page S20 and Figures S16−S20). 1 H NMR δ (ppm): 1.24−1.67 (m, 7H), 1.84−1.95 (m, 1H), 2.00− 2.18 (m, 2H), 3.35 (s, 3H), 3.50−3.58 (m, 3H), 3.72−3.62 (m, 9H), 4.25−4.32 (ddt, 1H, J = 2.0, 7.1, and 11.0 Hz), 5.46−5.52 (ddd, 1H, J = 1.2, 7.2, and 10.8 Hz), 5.65−5.73 (dddd, 1H, J = 1.5, 7.3, 9.0, and 10.7 Hz). 13 C NMR δ (ppm): 23.65, 26.20, 26.43, 29.14, 35.72, 58.98, 67.94, 70.48, 70.52, 70.58, 70.76, 71.89, 76.98, 129.99, 133.89. ESI−MS: m/z calcd, 272.1988; found, 272.2303. Anal. Calcd for C15H28O4: C, 66.2; H, 10.3; O, 23.5. Found: C, 65.3; H, 10.3; O, 24.4. 2-{[(2Z)-Cyclooct-2-en-1-yl]oxymethyl}tetrahydrofuran (T): The same procedure was followed as described for ME, using 3bromocyclooctene (76.5 g, 405 mmol) and tetrahydrofurfuryl alcohol (210 mL). The reaction mixture was stirred for 54 h at 50 °C. After purification, 2-{[(2Z)-cyclooct-2-en-1-yl]oxymethyl}tetrahydrofuran (22.8 g, 108 mmol, 27% yield, bp =102−105 °C at 0.08−0.12 Torr) was obtained as a colorless liquid (for details, see Supporting Information, page S26 and Figures S21−S25). 1 H NMR δ (ppm): 1.30−1.67 (m, 8H), 1.81−1.99 (m, 4H), 2.03− 2.19 (m, 2H), 3.34−3.38 (ddd, 1H, J = 3.4, 5.4, and 10.0 Hz), 3.49− 3.53 (ddd, 1H, J = 2.6, 5.4, and 10.0 Hz), 3.73−3.77 (m, 1H), 3.85− 3.89 (dddd 1H, J = 1.2, 6.1, 7.1, and 8.2 Hz), 4.00−4.08 (m, 1H), 4.25−4.31 (m, 1H), 5.47−5.53 (dddd, 1H, J = 1.4, 7.2, 9.9, and 11.0 Hz), 5.65−5.71 (dddt, 1H, J = 1.8, 7.2, 9.1, and 10.9 Hz). C

DOI: 10.1021/acs.macromol.6b00273 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 2. Characteristics of Hydrogenated Polymers Mn (kg mol−1) a

entry

product

precursor

9 10 11 12 13

HPM HPME HPME2 HPME3 HPT

PM (1) PME (2) PME2 (4) PME3 (6) PT (8)

b

convn (%)

yield (%)

calcd

>99 >99 >99 >99 >99

77 45 46 76 62

28 37 46 54 42

c

NMRd

SECe

Mw/Mne

42 40 46 54 56

53 101 115 76 69

1.7 1.5 2.4 3.5 2.6

a

The numbers in brackets are the entries in Table 1. bDetermined by 1H NMR spectroscopy from the ratio of integral areas between the remaining and original double bond. cMn,calcd = (MW of repeating unit) × [M]0/[G2]0 in Table 1 × fractional conversion in Table 1. dDetermined by endgroup analysis via 1H NMR measurement. eDetermined by SEC using polystyrene standards in THF at 40 °C. Poly{3-[2-(2-methoxyethoxy)ethoxy]-Z-cyclooct-1-ene} (PME2; for details, see Supporting Information, page S44 and Figures S36− S40). 1 H NMR δ (ppm): 1.24−1.43 (m, 7H), 1.55−1.65 (m, 1H), 2.01− 2.05 (dt, 2H, J = 7.0 and 7.0 Hz), 3.35−3.45 (m, 4H), 3.55−3.67 (m, 8H), 5.23 (dd, 1H, J = 8.5 and 15.5 Hz), 5.53 (dt, 1H, J = 6.5 and 15.5 Hz). 13 C NMR δ (ppm): 25.46, 29.28, 29.34, 32.30, 35.77, 59.10, 67.29, 70.53, 70.79, 72.04, 81.59, 130.86, 133.98. Anal. Calcd for C13H24O3: C, 68.4; H, 10.5; O, 21.1. Found: C, 67.4; H, 11.4; O, 21.2. Poly(3-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}-Z-cyclooct-1-ene) (PME3; for details, see Supporting Information, page S50 and Figures S41−S45). 1 H NMR δ (ppm): 1.22−1.46 (m, 7H), 1.54−1.65 (m, 1H), 1.98− 2.05 (dt, 2H, J = 7.0 and 6.8 Hz), 3.35−3.45 (m, 4H), 3.53−3.69 (m, 8H), 5.20−5.29 (dd, 1H, J = 8.5 and 15.5 Hz), 5.51−5.63 (dt, 1H, J = 6.5 and 15.5 Hz). 13 C NMR δ (ppm): 25.43, 29.29, 29.34, 32.28, 35.73, 59.06, 67.23, 70.54, 70.56, 70.65, 70.73, 71.97, 81.57, 130.81, 133.98. Anal. Calcd for C15H28O4: C, 66.2; H, 10.3; O, 23.5. Found: C, 64.9; H, 10.7; O, 24.4. Poly(2-{[(2Z)-cyclooct-2-ene-1-yl]oxymethyl}tetrahydrofuran) (PT; for details, see Supporting Information, page S56 and Figures S46−S50). 1 H NMR δ (ppm): 1.27−1.44 (m, 7H), 1.54−1.66 (m, 2H), 1.54− 1.66 (m, 2H), 1.82−2.03 (m, 5H), 3.17−3.25 (ddd, 1H, J = 5.3, 10.1, and 24.4 Hz), 3.43−3.50 (ddd, 1H, J = 5.3, 10.1, and 24.4 Hz), 3.53− 3.59 (ddt, 1H, J = 7.0, 7.0, and 14.5 Hz), 3.71−3.76 (ddt, 1H, J = 2.2, 6.9, and 8.5 Hz), 3.83−3.89 (dq, 1H, J = 6.6 and 8.5 Hz), 3.96−4.04 (tt, 1H, J = 6.7 and 11.6 Hz), 5.21−5.27 (ddd, 1H, J = 7.7, 8.4, and15.4 Hz), 5.52−5.58 (dt, 1H, J = 6.6 and 15.1 Hz). 13 C NMR δ (ppm): 25.46, 25.52, 25.62, 25.67, 28.43, 28.43, 29.23, 29.30, 32.32, 35.80, 35.86, 68.35, 68.39, 70.79, 70.90, 78.02, 78.33, 81.78, 81.85, 130.99, 131.01, 133.98, 134.12. Anal. Calcd for C13H22O2: C, 74.2; H, 10.6; O, 15.2. Found: C, 74.0; H, 10.6; O, 15.4. General Hydrogenation Procedure. A general procedure for the chemical hydrogenation of polymers is described for entry 13 in Table 2. The unsaturated PT (5.26 g, 25.0 mmol olefin) was dissolved in oxylene (50 mL) in a 500 mL three-neck round-bottom flask. ptoluenesulfonyl hydrazide (32.6 g, 175 mmol), tributyl amine (33.5 g, 181 mmol), and 3,5-di-tert-butyl-4-hydroxytoluene (ca. 5 mg) were added, and the reaction mixture was stirred at 140 °C for 6 h. The reaction mixture was allowed to cool to room temperature and was poured into a large, excess amount of methanol to precipitate the product. The hydrogenated polymer was collected by decantation and was purified by repeating precipitations using a THF/methanol system. The precipitate was collected as THF solution and was concentrated on a rotary evaporator. The polymer was dried in a vacuum oven at 40 °C overnight to afford hydrogenated poly(2{[(2Z)-cyclooct-2-ene-1-yl]oxymethyl}tetrahydrofuran) (HPT) as a slightly yellowish highly viscous liquid (3.68 g, 69% yield). The following is the complete list.

Hydrogenated PM (HPM; for details, see Supporting Information, page S62 and Figures S51−S55). 1 H NMR δ (ppm): 1.38−1.51 (m, 10H), 1.52−1.61 (m, 4H), 3.10 (p, 1H, J = 5.8 Hz), 3.44 (s, 3H). 13 C NMR δ (ppm): 25.39, 29.77, 29.98, 33.57, 56.46, 81.09. Anal. Calcd for C9H18O: C, 76.1; H, 12.7; O, 11.3. Found: C, 77.1; H, 13.2; O, 9.7. Hydrogenated PME (HPME; for details, see Supporting Information, page S68 and Figures S56−S60). 1 H NMR δ (ppm): 1.20−1.31 (m, 10H), 1.33−1.51 (m, 4H), 3.25 (p, 1H, J = 5.4 Hz), 3.38 (s, 3H), 3.52 (m, 2H), 3.58 (m, 2H). 13 C NMR δ (ppm): 25.58, 29.80, 29.98, 34.12, 59.08, 68.02, 72.48, 80.36. Anal. Calcd for C11H22O2: C, 71.0; H, 11.8; O, 17.2. Found: C, 69.8; H, 12.3; O, 17.9. Hydrogenated PME2 (HPME2; for details, see Supporting Information, page S74 and Figures S61−S65). 1 H NMR δ (ppm): 1.25−1.31 (m, 10H), 1.33−1.51 (m, 4H), 3.25 (p, 1H, J = 5.5 Hz), 3.37 (s, 3H), 3.51−3.66 (m, 8H). 13 C NMR δ (ppm): 25.57, 29.87, 30.01, 34.13, 59.12, 68.05, 70.58, 70.98, 72.05, 80.27. Anal. Calcd for C13H26O3: C, 67.8; H, 11.3; O, 20.9. Found: C, 67.5; H, 11.3; O, 21.2. Hydrogenated (HPME3; for details, see Supporting Information, page S80 and Figures S66−S70). 1 H NMR δ (ppm): 1.17−1.51 (m, 14H), 3.18−3.26 (p, 1H, J = 5.7), 3.50−3.69 (m, 12H) 3.38 (s, 3H). 13 C NMR δ (ppm): 25.62, 29.89, 30.80, 31.17, 59.11, 68.05, 70.62, 70.67, 70.72, 70.96, 72.03, 80.32. Anal. Calcd for C15H30O4: C, 65.7; H, 10.9; O, 23.4. Found: C, 66.4; H, 11.2; O, 21.4. Hydrogenated PT (HPT; for details, see Supporting Information, page S86 and Figures S71−S75). 1 H NMR δ (ppm): 1.19−1.53 (m, 14H), 1.56−1.66 (m, 1H), 1.79− 2.00 (m, 3H), 3.20−3.23 (p, 1H, J = 5.5 Hz), 3.33−3.37 (dd, 1H, J = 5.1 and 9.7 Hz), 3.43−3.49 (dd, 1H, J = 5.8 and 9.8 Hz), 3.71−3.76 (ddd, 1H, J = 2.1, 6.7, and 7.7 Hz), 3.84−3.88 (ddd, 1H, J = 2.1, 6.5, and 8.0 Hz), 3.97−4.02 (dddd, 1H, J = 1.8, 5.3, 7.2, and 12.6 Hz). 13 C NMR δ (ppm): 25.50, 25.56, 25.61, 28.50, 29.78, 29.96, 29.97, 34.04, 34.05, 68.29, 71.56, 78.20, 80.33. Anal. Calcd for C13H24O2: C, 73.5; H, 11.4; O, 15.1. Found: C, 73.6; H, 11.2; O, 15.2.

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RESULTS AND DISCUSSION Synthesis of Allylalkoxy-Functionalized Cyclooctenes. All allyl-alkoxy functionalized cyclooctenes were synthesized from 3-bromo-1-cyclooctene (3BrCOE) as previously reported (Scheme 2).27 The starting material 3BrCOE has high reactivity to nucleophiles,23 and substitution of the alkoxy group at the allyl position is readily achieved by simply mixing the 3BrCOE with a corresponding alcohol under alcoholysis condition. The monomer yield was reduced by increasing the bulkiness of the alcohols, increasing the number of ethylene glycol (EG) units and using the sterically hindered tetrahydrofurfuryl alcohol. D

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Macromolecules Scheme 2. Synthesis of 3-Alkoxy-Substituted Cyclooctenesa

was even lower than that of T, which has a tetrahydrofurfuryl group, the most rigid/bulky substituent. To obtain the polymers in high yield, large catalyst loading was necessary to overcome the low conversion (see entries 4, 6, and 8 in Table 1). The molecular weight of the obtained polymers measured by SEC relative to polystyrene standards was higher than the calculated value in all cases. This is presumably due to the discrepancy of hydrodynamic volume between the obtained polymers and polystyrene standards. On the other hand, the molecular weight determined by end-group analysis via 1H NMR spectroscopy was in close agreement with the calculated value. On the basis of the NMR characterization results, the number of average degrees of polymerization were certainly regulated to comparable values by adding cis-4-octene as a CTA. Although the SEC chromatogram showed a unimodal shape, the molecular weight distribution was broad (Mw/Mn = 1.3−2.8), in accordance with the typical values for ROMPproduced polymers.23 The ROMP reaction is accompanied by intermolecular chain transfer through secondary metathesis reactions between the propagating chain and alkenes in the polymer backbone. This intermolecular chain transfer reaction can lead to higher PDI values. Nevertheless, the tolerance of the Grubbs catalyst to polar functional groups enabled the ROMP of alkoxy-substituted monomers to yield polymers with ether side-chains. Generally, the ROMP of unsymmetrically substituted cyclooctenes results in polymers with regio- and stereomixed sequencesnamely, trans/cis-head-to-head (HH), trans/cis-tailto-tail (TT), and trans/cis-head-to-tail (HT).33−35 The regioand stereoregularity of the ROMP-produced polymers can be determined by NMR spectroscopy with relative ease, so the obtained polymers were characterized by 1H, 13C, and 2D NMR measurements. Although the polymers from less bulky substituted monomers exhibit minor signals that can be ascribed to regio-/stereoirregular sequences, all obtained polymers show only eight signals that are attributable to the backbone carbons in the 13C NMR spectra. Thus, the polymers possess a unified monomer unit orientation along the backbone (see Supporting Information, Figures S27, S32, S37, S42, and S47). Furthermore, the obtained polymers display only two predominant signals in the olefinic region, suggesting that the polymers have a single stereochemistry about the double bond (Figure 1). The regio- and stereochemistry can also be distinguished by 1H NMR spectroscopy. The 1H NMR spectra of the polymers exhibit two sets of olefinic signals with doublet of doublet (dd) and doublet of triplet (dt) multiplicity. The dd and dt multiplicities for two distinct olefinic signals are observed only if the polymers predominantly possess HT or HH-alt-TT regioregularity.27 Nevertheless, 1H−1H correlated spectra of all polymers exhibit clear cross peaks between the olefinic protons, suggesting that the polymers have HT regioregular sequences. Additionally, the coupling constants for olefinic protons were greater than 15 Hz for all polymers, consistent with the value for the trans double bond (Figure 2).28 When the NMR measurement results are considered, there is definite evidence of a trans-HT regioregular sequence for all polymers. These results are fully consistent with the previously reported analyses of regio- and stereoselective ROMP,23,24,26,27 which suggests that the polymers from alkoxy-substituted monomers also have remarkably high transHT regularity. The regio- and stereoselectivity in the ROMP of functionalized monomers are strongly affected by the polarity of the

a

R = methyl (M), 2-methoxyethyl (ME), 2-(2-methoxyethoxy)ethyl (ME2), 2-[2-(2-methoxyethoxy)ethoxy]ethyl (ME3), and (2tetrahydrofuranyl)methyl (T).

This approach considerably reduced the yield of the desired main products, allyl-alkoxy substituted cyclooctenes. It is noteworthy that the byproduct formed in the reaction was consistently 1,3-cyclooctadiene [bp = 55 °C/34 mmHg (lit.)], which can be readily removed by either passing purge N2 gas through the reaction mixture during the reaction period or fractional vacuum distillation. The allyl-alkoxy substituted cyclooctenes have a chiral carbon at the allyl-position, and the tetrahydrofurfuryloxy-substituted cyclooctene (T) contains two chiral centers at the allyl-position of the cyclooctene ring and tetrahydrofurfuryloxy group. Thus, for T, four isomeric configurations existnamely, RR, RS, SR, and SS. Consequently, the 1H and 13C NMR spectra of T exhibit duplication for several signals, indicating the existence of two diastereomeric forms (see Supporting Information). The structure of cyclooctenes was identified by NMR spectroscopy, the purity was established by NMR and MS measurements, and the obtained allyl-alkoxy functionalized cyclooctenes were used as monomers for the ROMP. Polymerization of Functionalized Monomers with G2. The ROMP of monomers was carried out in chloroform with G2 at room temperature for 20 h, as described.27 To compare the reactivity of the monomers, all monomers were polymerized under the same condition at a ratio of [M]0/ [G2]0 = 2500 in 2.0 M in CHCl3. To control the molecular weight of the polymers, cis-4-octene was included as a chain transfer agent (CTA), and the degree of polymerization was set at 200 ([M]0/([CTA]0 + [G2]0) = 200). The regio- and stereoselectivity in the ROMP of allyl-substituted monomers with ruthenium type Grubbs catalysts (G1,30 G2,31 and G332) were reported previously.27 The use of N-heterocyclic carbene (NHC)-ligated catalysts, G2 and G3, resulted in the polymers exhibiting similar regio- and stereoregularities. The regioselectivity was unaffected by the catalyst types G2 and G3; therefore, we chose G2 as the catalyst to synthesize the etherfunctionalized polymers from allylalkoxy substituted monomers. The results for the ROMP are summarized in Table 1. The polymerization systems are all homogeneous, and the reaction mixture showed a bright orange color during the polymerization. The polymerization was quenched by adding ethyl vinyl ether and stirring for 30 min at room temperature. The catalyst residue was removed by using a commercially available metal scavenger, which is a silica-supported dimercaptotriazine. The monomer conversion to polymer was nearly quantitative for M and ME (entries 1 and 2 in Table 1, respectively); however, the conversion was considerably low owing to the increased bulkiness of the substituent (see entries 3, 5, and 7 in Table 1). ME3 showed the lowest polymerization rate as 37% even after 20 h of polymerization. One explanation for this result might be that the flexible EG chain with an excluded volume effect, in which the EG chain prevents the monomer olefinic double-bond from accessing the catalytic center of G2. This is likely true, because the conversion of ME3 E

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Figure 1. Olefinic region of polymers.

13

selectivities are nearly unequivocally determined by the steric repulsion of the NHC ligand on G2 and the substituent at the allyl position of functionalized monomers. These data also demonstrate that the regularity of sequence orientations (HT, TT, and HT) can be effectively improved by tuning the bulkiness/rigidity of the substituent at the allyl-position of monomers. Hillmyer et al. reported on the regioselective ROMP of a series of allyl-substituted monomers with alkyl, phenyl, and polar functional groups, and the regioselectivity is strongly affected by the size of the substituent at the allyl position. 23,24,26,27 Among the previous reports for the regioselective ROMP of allyl-substituted monomers, phenylsubstituted monomer and a few examples exhibited nearly perfect trans-HT regioregularity.23,27 The present study shows that ROMP of T has a perfect regio-/stereoselectivity. Consequently, a new family of precision polyolefins was produced by regio-/stereoselective ROMP of tetrahydrofurfuryloxy-substituted cyclooctene. Synthesis of EVE Copolymers via Chemical Hydrogenation of ROMP-Produced Polymers. The ROMPproduced polymers were successfully saturated by a chemical hydrogenation reaction using p-toluenesulfonyl hydrazide, as previously reported.23,24,26,27,36 The polymers obtained in high conversion (Table 1, entries 1, 2, 4, 6, and 8) were used for the hydrogenation process as shown in Table 2. Although slight changes were found in the observed molecular weight by SEC, the molecular weight determined by NMR end-group analysis was in good agreement with the unsaturated versions of polymers in Table 1. The SEC chromatograms of the polymers still had a unimodal shape with a broad distribution. The introduction of an ether side-chain had no effect on the chemical hydrogenation, so the hydrogenated variants were readily produced. The olefinic signals completely disappeared from 1H and 13C NMR spectra, and the signals from the saturated main chain appeared at 1.2 to 1.7 ppm and 25 to 35 ppm in 1H and 13C NMR spectra, respectively. The 13C NMR spectra of the polymers exhibit precisely 6, 8, 10, and 12 signals for the HPM, HPME, HPME2, and HPME3, respectively. Notably, HPT exhibits several duplicated signals in the 10 signals that were observed; this is very likely because HPT still contains two chiral centers at the backbone and the tetrahydrofurfuryloxy group. These observations provide clear evidence for the high regioregularity of the unsaturated polymers and the establishment of a procedure for the synthesis of a series of precision EVE copolymers with precisely spaced branches on every eighth backbone carbon. Thermal Analysis and Surface Hydrophilicity Evaluation. Thermal analysis and surface hydrophilicity evaluation of the obtained polymers were performed for unsaturated and saturated polymers. DSC profiles of the polymers are shown in Figure 3, and the results are summarized in Table 3. Both Tg and Tm values were determined on the heating scan of the DSC measurement. Regardless of unsaturated or saturated versions, a monotonic decrease in Tg occurred with an increase in the number of EG units in the side-chain, whereas the polymer from T exhibited the highest Tg owing to the introduction of the bulky/rigid tetrahydrofurfuryloxy group. The unsaturated variants showed only a glass transition behavior during the heating scan from −72 to −41 °C, suggesting that the polymers were all in an amorphous state. In contrast, the saturated version of polymers showed a glass transition at −79 °C to −57 °C and endothermic peaks at −3.3 °C to −11 °C. Similar behavior is observed for the regularly branched precision

C NMR spectra for regioregular

Figure 2. Olefinic region of 1H−1H correlated spectrum PT.

systeme.g., solvent, functional groups at the monomer, and the temperature.24,28,29 The regio- and stereoregularity of the polymerizations in both nonpolar (e.g., toluene, cyclohexane) and highly polar (e.g., THF) solvents tend to lead to a decrease in the regio- and stereoselectivity. In the applied polymerization condition, in which the monomer concentrations are the same, the introduction of a longer oligo(ethylene glycol) chain into the monomer could lead to an increase in the polarity of the polymerization system; therefore, the regularity would likely be reduced. However, increasing the number of EG units in the chain improves both trans-stereoregularity and HT regioregularity. Moreover, the ROMP of T in the applied condition generated polymers with high regio- (HT content >99%) and stereo- (trans- content >99%) regularities, whereas T has a THF moiety in the monomer framework. This demonstrates how the regio- and stereoselectivity are determined, and the F

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Figure 3. DSC profiles of obtained polymers at a heating rate of 5 °C/min. (a) unsaturated polymers: PM (1), PME (2), PME2 (3), PME3 (4), and PT (5). (b) Saturated polymers: HPM (6), HPME (7), HPME2 (8), HPME3 (9), and HPT (10).

would be an effective way to increase the hydrophilicity; however, PT showed a hydrophobic character. Interestingly, the water contact angle on the hydrogenated polymers showed very similar values ranging from 81° to 87°, which was slightly lower than that of the unsubstituted polyethylene (91°). This might be the result of two factors: (1) immiscibility of the hydrophobic backbone and the hydrophilic side-chain, and (2) surface free energy. The hydrogenated polymers are semicrystalline, exhibiting a broad endothermic peak (Tm) on the heating scan of DSC. This is a hallmark in which the hydrophobic backbone chains aggregate to crystallize and the hydrophilic side-chains are excluded to the amorphous phases.37 This segregation might induce the formation of a lamellar-like backbone and side-chain phases that could potentially result in the formation of a hydrophobic “hydrocarbon-covered surface” to minimize interfacial free energy at the air−polymer interface. This postulation is currently being tested by examining the difference between regioregular and regioirregular polymers and will be reported in the future.

Table 3. Thermal and Hydrophilicity Characteristics of Polymers unsaturated

saturated

Ra

Tgc (°C)

CAd (deg)

Tgc (°C)

Tmc (°C)

CAd (deg)

b

−89 −56 −59 −68 −72 −41

83 77 72 50 29 76

− −68 −70 −73 −79 −57

130 4.5 −3.3 2.0 0.4 11

91 87 83 87 84 81

H M ME ME2 ME3 T a

Substituent identity. bPolycyclooctene (unsaturated) and polyethylene (saturated) prepared from cyclooctene with the identical condition. cDetermined by DSC measurement performed with a rate of 5 °C/min. dWater contact angle determined with the sessile drop method.

LLDPEs, which were synthesized by the ADMET polymerization, reported by Wagener et al.37−39 Additionally, a broad exothermic peak was observed between the glass transition and the endothermic peak. We speculate that the broad exothermic peak is attributable to the low-temperature crystallization of polymers, which are in a supercooled state, whereas the endothermic peak is due to melting of the crystallized polymers. One notable difference exists between the present study and the previously reported alkyl-substituted regioregular polymers. The alkyl-substituted polymers with long alkyl chains (e.g., ethyl and hexyl) are amorphous even after the saturation of the backbone.27 However, the saturated variants in this study are semicrystalline in all cases. This could be the result of the changes in chain-packing. Further investigation is required to elucidate the disparity between the alkyl- and ether-substituted polymers. The hydrophilicity of the obtained polymers was investigated by water contact angle measurement using the sessile drop method. All obtained polymers were insoluble in water, so the measurement was carried out with polymer-coated PET substrate. The hydrophilicity of unsaturated polymers increased with increasing number of EG units in the side-chain, and the water contact angle monotonically decreased. PME3 exhibited the lowest water contact angle value (29°), indicating the presence of a hydrophilic surface with high water affinity. We predicted that the introduction of a tetrahydrofurfuryloxy group

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CONCLUSIONS The allyl-substituted monomers with ether side-chains were synthesized and polymerized with G2 catalyst. The functionalized monomers underwent ROMP in regio- and stereoselective manners to provide the polymers with extensively high trans-head-to-tail sequence regularity. The regioselectivity of the polymers increased with increasing length/size of the substituent, and the ROMP of the tetrahydrofurfuryloxysubstituted monomer showed the highest regio- and stereoselectivity, greater than 99%. The resulting polymers were successfully hydrogenated with chemical hydrogenation and then readily converted to the saturated variants possessing precisely placed side-chain branches on every eighth backbone carbon as we previously reported. The thermal properties of the obtained polymers were analyzed by DSC. Interestingly, all saturated polymers exhibited melting behavior during the heating process. However, the unsaturated counterparts did not show any crystallization/melting behavior, suggesting that the functionalized polyalkenamers are amorphous. The hydrophilicity of the polymers was changed by varying the number of EG units and the side-chain structure; a longer EG chain gave the polymers a more hydrophilic nature. G

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(13) Wagener, K. B.; Boncella, J. M.; Nel, J. G. Acyclic diene metathesis (ADMET) polymerization. Macromolecules 1991, 24, 2649−2657. (14) Lehman, S. E.; Wagener, K. B. ADMET Polymerization. In Handbook of Metathesis, 1st ed.; Grubbs, R. H., Ed.; Wiley: New York, 2003; Vol. 3, pp 283−353. (15) Baughman, T. W.; Wagener, K. B.; Buchmeiser, M. R. Recent Advance in ADMET Polymerization. Adv. Polym. Sci. 2005, 176, 1−42. (16) Boz, E.; Wagener, K. B. Progress in the development of welldefined ethylene-vinyl halide polymers. Polym. Rev. 2007, 47, 511− 541. (17) Lehman, S. E., Jr.; Wagener, K. B.; Baugh, L. S.; Rucker, S. P.; Schulz, D. N.; Varma-Nair, M.; Berluche, E. Linear copolymers of ethylene and polar vinyl monomers via olefin metathesis-hydrogenation: Synthesis, characterization, and comparison to branched analogues. Macromolecules 2007, 40, 2643−2656. (18) Wagener, K. B.; Berda, E. B. Precision Polyolefins. In Complex Macromolecular Architectures: Synthesis, Characterization, and SelfAssembly, Hadjichristidis, N., Hirao, A., Tezuka, Y., Du Prez, F., Eds.; Wiley (Asia): Singapore, 2011, 317−347. (19) Blencowe, A.; Qiao, G. G. Ring-Opening Metathesis Polymerization with the Second Generation Hoveyda-Grubbs Catalyst: An Efficient Approach toward High-Purity Functionalized Macrocyclic Oligo(cyclooctene)s. J. Am. Chem. Soc. 2013, 135, 5717−5725. (20) Breitenkamp, R. B.; Ou, Z.; Breitenkamp, K.; Muthukumar, M.; Emrick, T. Synthesis and characterization of polyolefin-graftoligopeptide polyelectrolytes. Macromolecules 2007, 40, 7617−7624. (21) Gorodetskaya, I. A.; Gorodetsky, A. A.; Vinogradova, E. V.; Grubbs, R. H. Functionalized Hyperbranched Polymers via Olefin Metathesis. Macromolecules 2009, 42, 2895−2898. (22) Mes, T.; Smulders, M. M. J.; Palmans, A. R. A.; Meijer, E. W. Hydrogen-Bond Engineering in Supramolecular Polymers: Polarity Influence on the Self-Assembly of Benzene-1,3,5-tricarboxamides. Macromolecules 2010, 43, 1981−1991. (23) Martinez, H.; Zhang, J.; Kobayashi, S.; Xu, Y.; Pitet, L. M.; Matta, M. E.; Hillmyer, M. A. Functionalized regio-regular linear polyethylenes from the ROMP of 3-substituted cyclooctenes. Appl. Petrochem. Res. 2015, 5, 19−25. (24) Zhang, J.; Matta, M. E.; Martinez, H.; Hillmyer, M. A. Precision Vinyl Acetate/Ethylene (VAE) Copolymers by ROMP of AcetoxySubstituted Cyclic Alkenes. Macromolecules 2013, 46, 2535−2543. (25) Jeong, H.; Kozera, D. J.; Schrock, R. R.; Smith, S. J.; Zhang, J.; Ren, N.; Hillmyer, M. A. Z-Selective Ring-Opening Metathesis Polymerization of 3-Substituted Cyclooctenes by Monoaryloxide Pyrrolide Imido Alkylidene (MAP) Catalysts of Molybdenum and Tungsten. Organometallics 2013, 32, 4843−4850. (26) Zhang, J.; Matta, M. E.; Hillmyer, M. A. Synthesis of SequenceSpecific Vinyl Copolymers by Regioselective ROMP of Multiply Substituted Cyclooctenes. ACS Macro Lett. 2012, 1, 1383−1387. (27) Kobayashi, S.; Pitet, L. M.; Hillmyer, M. A. Regio- and Stereoselective Ring-Opening Metathesis Polymerization of 3Substituted Cyclooctenes. J. Am. Chem. Soc. 2011, 133, 5794−5797. (28) Martinez, H.; Hillmyer, M. A.; Cramer, C. J. Factors Controlling Selectivity in the Ring-Opening Metathesis Polymerization of 3Substituted Cyclooctenes by Monoaryloxide Pyrrolide Imido Alkylidene (MAP) Catalysts. J. Org. Chem. 2014, 79, 11940−11948. (29) Martinez, H.; Miro, P.; Charbonneau, P.; Hillmyer, M. A.; Cramer, C. J. Selectivity in Ring-Opening Metathesis Polymerization of Z-Cyclooctenes Catalyzed by a Second-generation Grubbs Catalyst. ACS Catal. 2012, 2, 2547−2556. (30) Schwab, P.; Grubbs, R. H.; Ziller, J. W. Synthesis and Applications of RuCl2(:CHR′) (PR3)2: The Influence of the Alkylidene Moiety on Metathesis Activity. J. Am. Chem. Soc. 1996, 118, 100−110. (31) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Synthesis and activity of a new generation of ruthenium-based olefin metathesis catalysts coordinated with 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ligands. Org. Lett. 1999, 1, 953−956.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b00273. Preparation of monomers and analytical data, general polymerization procedure and analytical data, general chemical hydrogenation procedure and analytical data, detailed NMR structural assignments and NMR spectra (1H, 13C, DEPT135, 1H−1H COSY, and HMQC) for obtained products (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*(S.K.) E-mail: [email protected]. *(M.T.) E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS S.K. gratefully acknowledges financial support from JSPS KAKENHI (No. 24750097 and No. 15K05512) of Japan Society of the Promotion of Science (JSPS). M.T. acknowledges financial support from the Funding Program for NextGeneration World-Leading Researchers (NEXT Program) of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan and the Center of Innovation Program from the Japan Science and Technology Agency (JST).

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