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Synthesis of Novel Cyclic Olefin Copolymer (COC) with High Performance via Effective Copolymerization of Ethylene with Bulky Cyclic Olefin. Miao Hongâ...
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Synthesis of Novel Cyclic Olefin Copolymer (COC) with High Performance via Effective Copolymerization of Ethylene with Bulky Cyclic Olefin Miao Hong,†,‡ Lei Cui,† Sanrong Liu,† and Yuesheng Li*,† †

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

ABSTRACT: Novel cyclic olefin copolymer (COC) with high glass transition temperature, good mechanical performance, high transparency, and excellent film forming ability has been achieved in this work by effective copolymerization of ethylene and exo-1,4,4a,9,9a,10hexahydro-9,10(1′,2′)-benzeno-l,4-methanoanthracene (HBMN). This bulky cyclic olefin comonomer can be simply prepared in good yield via Diels−Alder reaction. By utilizing constrained geometry catalyst (CGC) activated with Al(iBu)3/[Ph3C][B(C6F5)4], ethylene/HBMN copolymer can be obtained with excellent production, high molecular weight, and a wide range of HBMN incorporation. 13C NMR (DEPT) spectra reveal alternating ethylene−HBMN sequence can be detected at high HBMN incorporation. The glass transition temperature (Tg) of resulted copolymer enhances with increasing HBMN incorporation. A high Tg up to 207.0 °C is attainable at low comonomer incorporation of 30.4 mol %, which is 61 °C higher than that of commercial norbornene (NB)derived COC (54 mol %). The tensile test indicates that the ethylene/HBMN copolymer has good mechanical performance which is more flexible than ethylene/NB copolymer and the previously reported COC even at a higher Tg level.

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INTRODUCTION Cyclic olefin copolymer (COC), prepared via the copolymerization of cyclic olefin with ethylene or α-olefin, is one of the most important engineering plastics and has been used in heat-resistant and optical applications because of its unique advantages such as high transparency, low density, high heat stability, and good chemical resistance.1,2 Through varying the comonomer employed and the comonomer content, the properties of COCs can be easily controlled. At present, COCs have been commercialized by Mitsui and Ticona under the trade names of APEL and Topas, respectively.3 Ethylene/norbornene(NB) copolymer (1 in Scheme 1) is the representative COC.4,5 However, a main demerit of the NB-derived COC is the brittleness, especially in the case of high glass transition temperature (Tg), which has significantly hampered its many end uses.6 For example, if Tg reaches the level of common transparent resin such as polycarbonate (Tg = 150 °C), NB content need to be up to 54 mol %. At such high NB content, the polymer chain is so rigid that the chain entanglement is low, which results in the brittleness. Academic and industrial communities have paid much attention to improve the mechanical performance of COC without the loss of high Tg. One approach to overcome this brittle problem may be the employment of a bulky cyclic olefin comonomer. After less incorporation of bulky cyclic olefin comonomer, a higher amount of flexible ethylene units in the COC is attainable at the same level of Tg, resulting in high chain entanglement, and thus © 2012 American Chemical Society

Scheme 1. Structures of COCs in Previous Reports and the Synthetic Route of Ethylene/HBMN Copolymer in This Study

may lead to the improved mechanical performance. Ethylene/ dicyclopentadiene (DCPD) copolymer (2 in Scheme 1) is the typical COC which is usually used to replace ethylene/NB copolymer,7 but the alternating ethylene/DCPD copolymer does not exhibit satisfyingly high Tg at low comonomer content. For instance, Hou et al. reported alternating ethylene/ Received: April 9, 2012 Revised: June 7, 2012 Published: June 22, 2012 5397

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DCPD copolymer with Tg of 125 °C at 45 mol % content by using cationic scandium catalyst system.7a Kaminsky and coworkers introduced 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene (DMON) to prepare the COC (3 in Scheme 1). However, the ethylene/DMON copolymer at high content (44 mol %) was reported not to be amorphous but semicrystalline, showing a melting point at 380 °C.8 Recently, Lee et al. utilized o-phenylene-bridged CGC analogues to produce the ethylene/dihydrotricyclopentadiene (HTCPD) copolymer (4 in Scheme 1) with a high Tg of 177 °C (HTCPD mol % = 45%), which is much higher than that of the ethylene/NB copolymer at the same cyclic olefin content.6 Whereas, the HTCPD-derived COC is still brittle as the strain at break is 2.8% (Tg = 154 °C), which is only slightly higher than that of commercial NB-derived COC [strain at break (ε) = 2.1%, Tg = 146 °C). In the following work of Lee’s group,9 Tg as high as 214 °C at the comonomer content of 41 mol % has been achieved in ethylene/tricyclopentadiene (TCPD) copolymer (5 in Scheme 1) using [Ph2C(Flu)(Cp)]ZrCl2 as a catalyst. The tensile test of this copolymer was not contained in this report. Up to now, despite many investigations have been carried out, COC simultaneously possessing high Tg and improved mechanical performance has not been reported yet. Herein, we report a new COC prepared via the copolymerization of ethylene with exo-1,4,4a,9,9a,10-hexahydro-9,10(1′,2′)-benzeno-l,4-methanoanthracene (HBMN) (6 in Scheme 1) using constrained geometry catalyst (CGC, [Me2Si(η5-Me4C5)(NtBu)]TiCl2) which has the excellent ability in incorporating a bulky monomer due to its open nature of catalytic active site.10,11 Upon utilizing this novel bulky cyclic olefin comonomer, a high Tg up to 207.0 °C is attainable at low comonomer incorporation of 30.4 mol %. The obtained copolymer exhibits favorable mechanical performance (ε = 7.6%, Tg = 160.4 °C) which is more flexible than ethylene/ NB copolymer (ε = 2.7%, Tg = 126.4 °C) and previously reported HTCPD-derived COC (ε = 2.8%, Tg = 154.0 °C) even at higher Tg level. Another merit of HBMN-derived COC is that the remaining aromatic ring can be further participated in the following functionalization, resulting in functional polyolefins which are also under great interest of researchers.12,13

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The tests were conducted at room temperature using a cross-head rate of 5 mm/min according to the ASTM standard. The data reported were the mean and standard deviation from five determinations. The transparency of copolymer film is recorded on a Shimadzu UV-3600 spectrophotometer. Anhydrous solvents used in this work were purified by Solvent Purification System purchased from Mbraun. Anthracene and norbornadiene were purchased from Acros and used without further purification. Triisobutylaluminium [Al(iBu)3] was purchased from Akzo Nobel Chemical Inc. and used without further purification. Trityl tetrakis(pentafluorophenyl)borate ([Ph3C][B(C6F5)4]) was purchased from Aldrich and used without further purification. Constrained geometry catalyst (CGC) was synthesized according to the previous report.11,14 Synthesis of HBMN Comonomer. The synthesis was carried out according to the procedure reported in the previous literature with some modification.15 A sealed autoclave containing anthracene (42 g, 0.23 mol) and norbornadiene (108 g, 1.2 mol) under a nitrogen atmosphere was heated at 180 °C for 24 h in an oil bath. After cooling, a white precipitate formed which was separated from the liquor by filtration. The norbornadiene was stripped from the reaction mixture at reduced pressure, giving a yellow residue. Three 200 mL portions of petroleum ether were added to the combined precipitates, and the mixture was stirred at 50 °C for 10 min and then filtered. The combined filtrate was concentrated under vacuum to a suitable volume and recrystallized to give the pure product as white crystalline material (50.2 g, 80%). Then a desired amount of toluene was added until the concentration of HBMN reached 2 mol/L, and the obtained solution was stored under nitrogen for further use. Typical Copolymerization Procedure. Copolymerizations were carried out under atmospheric pressure in toluene in a 150 mL glass reactor equipped with a mechanical stirrer. The total volume of the solution was 30 mL. The reactor was charged with prescribed volume of toluene and comonomer under a nitrogen atmosphere, and then the ethylene gas feed was started, followed by the addition of Al(iBu)3 and [Ph3C][B(C6F5)4] to the reactor. After equilibration at the desired polymerization temperature for 10 min, the polymerization was initiated by the addition of toluene solution of the catalyst. After a desired period of time, the reactor was vented. The resulting copolymers were precipitated from hydrochloric acid/ethanol (2 vol %), filtered, washed three times with ethanol, then marinated in acetone for 12 h to remove the unreacted comonomer, and then dried in vacuo at 60 °C to a constant weight. Preparation of Film. In a 50 mL round-bottom flask, the desired polymer and o-xylene were added (15 wt %) and the mixture was heated at 40 °C. After the complete dissolution, the thick solution was filtered using a filter. The obtained solution was spread on a glass plate in an oven with a nitrogen atmosphere. The solvent in the spread film was carefully evaporated at 80 °C for 6.0 h. Then the film was further dried at 100 °C for about 12 h. After the evaporation, the thickness of obtained film was measured about 70−90 μm.

EXPERIMENTAL SECTION

General Procedure and Materials. All work involving air and/or moisture sensitivity was carried out in a MBraun glovebox or under a nitrogen atmosphere by using the standard Schlenk technique. All 1H and 13C NMR spectra were recorded on a Varian Unity-400 MHz spectrometer (399.65 MHz for 1H, 100.40 MHz for 13C). The incorporation of NB in ethylene/NB copolymer is calculated according to previous report.4g The molecular weights (MWs) and molecular weight distributions of the polymer samples were determined at 150 °C by a PL-GPC 220 type high-temperature gel permeation chromatography. 1,2,4-Trichlorobenzene (TCB) was employed as the solvent at a flow rate of 1.0 mL/min, and the calibration was made by polystyrene standard Easi-Cal PS-1 (PL Ltd.). The FT-IR spectra were recorded on a Bio-Rad FTS-135 spectrophotometer. Differential scanning calorimetry (DSC) measurements were performed on a Perkin-Elmer Pyris 1 DSC instrument under a nitrogen atmosphere. The samples were heated at a rate of 20 °C/min and cooled down at a rate of 20 °C/min. Thermogravimetric analytic (TGA) measurements were performed with a Perkin-Elmer Pyris 1 thermogravimetric analyzer with a heating rate of 20 °C/min in nitrogen and air. Tensile tests were performed on a 8.9 kN, screwdriven universal testing machine (Instron 1211, Canton, MA) equipped with a 10 kN electronic load cell and mechanical grips.

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RESULTS AND DISCUSSION Ethylene/HBMN Copolymerization. The HBMN comonomer was prepared through the Diels−Alder reaction of anthracene and norbornadiene at 180 °C. After the simple extraction using hot petroleum ether and following recrystallization, the pure HBMN comonomer is obtained as the white crystalline solid with a good yield of 80%. During the reaction, the excess norbornadiene is necessary to restrict the successive Diels−Alder reaction between the remaining double bond of HBMN and anthracene as well as to ensure the complete reaction of anthracene as the unreacted anthracene is difficult to separate from the product. When the molar ratio of norbornadiene and anthracene is about 5, the reaction can be controlled well with complete reaction of anthracene after 24 h and low occurrence of successive Diels−Alder reaction. The unreacted norbornadiene can also be recycled after the reaction. 5398

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Table 1. Results of Ethylene/HBMN Copolymerization by CGCa entry

comon (mmol)

[comon]/[E]b

temp (°C)

yield (g)

activityc

incorpd (mol %)

Mwe (kg/mol)

PDIe

Tgf (°C)

1 2 3 4 5 6 7 8g

2.0 2.0 2.0 4.0 7.5 10 20 32

0.617 0.787 0.980 1.574 2.951 3.935 7.871 12.59

40 60 80 60 60 60 60 60

2.20 3.10 1.55 3.75 4.70 5.00 5.40 4.00

8.80 12.4 6.20 15.0 18.8 20.0 21.6 16.0

7.60 9.50 11.4 12.0 16.0 20.2 30.4 46.5

415 205 173 330 360 400 439 519

1.76 1.84 1.67 2.25 1.97 1.89 1.97 1.83

70.8 78.0 80.0 83.5 125.5 160.4 207.0 126.4

Conditions: catalyst 3 μmol, Al(iBu)3 0.75 mmol, [Ph3C][B(C6F5)4] 18 μmol, ethylene 1 atm, Vtotal = 30 mL, reaction time =5 min. bMolar ratio of comonomer to ethylene in feed (ethylene concentrations in toluene can be calculated according to the Henry−Gesetz expression5a,16). cCatalytic activity: kg polymer/(mmolTi h). dComonomer incorporation (mol %) established by 1H NMR spectra. eWeight-average molecular weights and polydispersity indices determined by GPC at 150 °C in 1,2,4-C6Cl3H3 vs narrow polystyrene standards. fGlass transtion temperatures were measured by DSC. gCopolymerization of ethylene with norbornene under the same conditions. a

The 1H and 13C NMR spectra of HBMN comonomer are provided in Figures S1 and S2 (see Supporting Information). As observed, every peak can be assigned clearly without any impurity peaks, and all integrations match very well, indicating the high purity of HBMN comonomer. In the presence of Al(iBu)3 and [Ph3C][B(C6F5)4], the CGC is highly active toward ethylene/HBMN copolymerization. In order to minimize the change of monomer feed ratio during the copolymerization, the copolymerizations were conducted for 5 min. The typical results are summarized in Table 1. It is found that the catalytic performance is strongly influenced by the reaction conditions. Raising reaction temperature from 40 to 80 °C (Table 1, entries 1−3), the catalytic activity first increases and then decreases while the MW of the copolymer decreases gradually and the HBMN incorporation enhances. Because the highest activity can be achieved at 60 °C, the following copolymerizations are carried out at 60 °C. Under the optimum conditions, the catalytic activities are extremely high and all above 10 000 kg/(molTi h). It is noteworthy that a significant increase is detected not only in the catalytic activity but also in the MW and HBMN incorporation with increasing the HBMN concentration in feed (Table 1, entries 4−7). The highest HBMN incorporation up to 30.4 mol % has been achieved with the activity of 21 600 kg/(molTi h) (Table 1, entry 7). Moreover, the MWs of the resulted copolymers are significantly high in the range of 170−440 kg/mol. All the copolymers exhibit unimodal molecular weight distributions (PDI = 1.7− 2.3), which is consistent with the single homogeneous catalytic species. It deserves to mention that the unpolymerized comonomer after the copolymerization can be recycled just by recrystallization in petroleum ether. The 1H and 13C NMR spectra are used to fully characterize the structure of the ethylene/HBMN copolymer. The representative 13C NMR spectra along with the assignment are shown in Figure 1. Through the analysis of 13C NMR spectra in combination with 13C DEFT (distortionless enhancement of polarization transfer) spectra, the peaks are unambiguously assigned. Those peaks in the region of 122−145 ppm are ascribed to the carbons of the aromatic rings, while those peaks in the region of 27−50 ppm are attributed to the carbons of cyclic rings and ethylene units. The absence of double bond indicates that the copolymerization proceeds through the vinyl addition type. Moreover, when the HBMN incorporation increases, the 13C NMR spectra are slightly different from those with low incorporation. Compared with Figure 1a, new peaks at 45.6 and 48.5 ppm [marked as 10,10′

Figure 1. Typical 13C NMR and DEPT 135 spectra of ethylene/ HBMN copolymers in o-C6D4Cl2 at 125 °C: (a) HBMN mol % = 7.60% (Table 1, entry 1); (b) HBMN mol % = 30.4% (Table 1, entry 7); (c) DEPT (135) spectrum for HBMN mol % = 30.4%.

(alt) and 9,9′ (alt)] can be tracked in Figure 1b, which are attributed to the alternating ethylene−HBMN sequence. In all cases, the continuous HBMN−HBMN sequence is not detected, which can be clearly explained by steric congestion of titanium active species associated with the successive insertion of HBMN units. It is consistent with the fact that CGC exhibits no catalytic activity in an attempted homopolymerization of HBMN. A typical 1H NMR spectrum of ethylene/HBMN copolymer is provided in Figure 2. The peaks at 6.80−7.21 ppm are attributed to the protons of the aromatic rings. The protons of methines near the aromatic rings are detected at 4.20 ppm. The peaks in the region of 0.70−1.92 ppm are ascribed to the protons of cyclic rings and ethylene units. The signal of bridged methylene is split into two peaks at 0.54 and −0.56 ppm, which is caused by the anisotropy of benzene moiety. A similar phenomenon can also be observed in the 1H NMR spectrum of HBMN comonomer. In all 1H NMR spectra of the copolymers, these peaks appeared clearly. The HBMN incorporations of the copolymers were therefore calculated from the relative intensities of these protons using the equation 5399

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three degradation steps. The first weight loss (Tmax: about 380 °C) is probably attributed to the degradation of the cyclic moiety, while the second weight loss (Tmax: about 450 °C) is attributed to the degradation of ethylene unit on the main chain. These two degradation steps lost more than 90% weight. Mechanical Properties of HBMN-Derived COCs. Because of the rigidness of polymer chain and the lack of chain entanglement, the traditional NB-derived COC is very brittle which has significantly hampered its many end uses. The ethylene/HBMN copolymer in present work exhibits the unique character which contains a higher amount of flexible ethylene units even at the higher Tg level. Therefore, this copolymer may be promising in possessing the improved mechanical performance without the loss of high Tg. To prove it, the tensile test was carried out. For comparison, the ethylene/NB copolymer with NB incorporation of 46.5 mol % and Tg of 126.4 °C was also prepared using CGC (Table 1, entry 8). The polymer films were obtained by the solution casting from a copolymer solution in o-xylene (15 wt %). Since the MWs of ethylene/HBMN copolymers are high enough, the self-standing films can be easily formed. After the careful evaporation of solvent, the homogeneously transparent films with the thickness about 70−90 μm were obtained. The stress−strain behaviors were measured under the similar conditions to previous report.6 The typical results are provided in Table 2. For the ethylene/HBMN copolymer with Tg of 125.5 °C, a high strain at break of 14.0% is observed (Table 2, entry 1). With increase of Tg, the strain at break of copolymer decreases gradually (Table 2, entries 1−3). Even so, these values are much higher than that of the ethylene/NB copolymer. Take the ethylene/HBMN copolymer with incorporation of 20.4 mol % as an example. Generally, the brittleness of COC is more severe for a polymer with higher Tg. In present work, the Tg (160.4 °C) of ethylene/HBMN copolymer is significantly higher than that of ethylene/NB copolymer (126.4 °C), but ethylene/HBMN copolymer is more flexible with the strain at break reached at 7.6%, which is nearly 3 times higher than that of ethylene/NB copolymer (2.7%) (Table 2, entry 2 vs 4). Additionally, compared with the previously reported ethylene/HTCPD copolymer (2.8%, 154.0 °C),6 the present ethylene/HBMN copolymer is also much more flexible at the similar level of Tg (7.6%, 160.4 °C) (Table 2, entry 2 vs 5). The enhanced flexibility can be clearly explained by the increased chain entanglement as the copolymer contains higher amount of flexible ethylene units. Moreover, it is interesting to note that not only the strain at break but also the most tensile strength and tensile modulus are higher than those of ethylene/NB copolymer and ethylene/ HTCPD copolymer. The typical stress−strain curves are presented in Figure 3. A plateau can be observed at break, especially for ethylene/

Figure 2. 1H NMR spectrum of ethylene/HBMN copolymer (HBMN mol % = 30.4%, Table 1, entry 7) in C2D2Cl4 at 100 °C.

HBMN mol % = [2I4.20ppm /(I0.70−1.92ppm − I4.20ppm)] (1)

× 100%

where I4.20ppm is the intensity of protons at 4.20 ppm and I0.70−1.92ppm is the total intensity of protons at 0.70−1.92 ppm. The thermal transition temperatures of ethylene/HBMN copolymers are examined by DSC analyses. The typical second heating scans of DSC curves are shown in Figure S3 (see Supporting Information). When HBMN incorporation is higher than 7.60 mol %, the copolymer is amorphous and does not exhibit any melting temperature. The Tg value of resulted copolymer enhances with increasing HBMN incorporation (Table 1, entries 4−7). The high Tg up to 207.0 °C is attained at low cyclic olefin incorporation of 30.4 mol % (Table 1, entry 7), which is 61 °C higher than that of commercial NBderived COC (Tg = 146 °C, NB mol % = 54%).6 Moreover, even compared with ethylene/TCPD copolymer which represents the best result reported so far,9 Tg of present copolymer is still significantly high at the similar cyclic olefin incorporation (TCPD mol % = 31%, Tg = 163 °C; HBMN mol % = 30.4%, Tg = 207.0 °C). As far as we know, this high Tg obtained at such low cyclic olefin incorporation is unprecedented among the reported COCs. The thermal stability of ethylene/HBMN copolymer is studied by TGA. The typical TGA curves and relative derivative thermogravimetry (DTG) curves are shown in Figure S4 (see Supporting Information). The onset degradation temperatures (Td) are defined by the temperatures of 10% weight loss in TGA curves, and the maximum degradation temperatures (Tmax) are evaluated by the peaks in DTG curves. Copolymers with different HBMN incorporations exhibit similar thermal stability. A high Td at around 340 °C in N2 or air can be observed, demonstrating high thermal stability. Moreover, TGA analyses also indicate that ethylene/HBMN copolymer displays Table 2. Tensile Properties of HBMN-COC Filmsa entry

sample

Tg (°C)

Mw (kg/mol)

incorp (mol %)

εb (%)

σc (MPa)

Ed (MPa)

1 2 3 4 5e

HBMN-COC HBMN-COC HBMN-COC NB-COC HTCPD-COC

125.5 160.4 207.0 126.4 154.0

360 407 439 519 190

16.0 20.2 30.4 46.5 37.0

14.0 7.60 2.90 2.70 2.80

63.3 55.0 52.2 47.8 30.0

2680 2590 2460 2580 2100

Samples (ca. 80 μm thick) were prepared via solution casting and were measured at cross-head rate of 5 mm/min. bStrain at break. cTensile strength. dTensile modulus. eEthylene/HTCPD copolymer in a previous report.6 a

5400

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as the catalyst system, a series of ethylene/HBMN copolymer can be obtained with excellent production, high molecular weight, and a wide range of HBMN incorporation. 13C NMR (DEPT) spectra reveal alternating ethylene−HBMN sequence can be detected at high HBMN incorporation. The Tg value of resulting copolymer enhances with increasing HBMN incorporation. A high Tg up to 207.0 °C is attainable at low comonomer incorporation of 30.4 mol %, which is 61 °C higher than that of commercial NB-derived COC (54 mol %). The tensile test indicates that the ethylene/HBMN copolymer has good mechanical performance (ε = 7.6%, Tg = 160.4 °C) which is more flexible than ethylene/NB copolymer (ε = 2.7%, Tg = 126.4 °C) and previously reported HTCPD-derived COC (ε = 2.8%, Tg = 154.0 °C) even at higher Tg level. To our knowledge, the present copolymer is the first example of COC which simultaneously possesses high Tg and improved mechanical performance. Besides, ethylene/HBMN copolymer also has the merit of high transparency and good film forming ability. Convenient synthesis, excellent production, and high performance enable the present HBMN-derived COC to be promising in practical application. The remaining aromatic ring in ethylene/HBMN copolymer is also very versatile because it can be further participated in the following functionalization (such as the sulfonation, see Supporting Information), resulting in functional polyolefins. The syntheses of various functional polyolefins with different functional group contents as well as the performance investigation for functional polyolefins are currently in progress.

Figure 3. Tensile stress−strain curves for (a) ethylene/HBMN copolymer (ε = 7.60%, Table 2, entry 2) and (b) ethylene/NB copolymer (ε = 2.70%, Table 2, entry 4).

HBMN copolymer with high strain at break (ε = 7.6%, Figure 3a). It is a noticeable difference between the ethylene/HBMN copolymer and highly brittle ethylene/NB copolymer which breaks without displaying any plateau. Because of the presence of plateau, ethylene/HBMN copolymer displays the flexibility. To the best of our knowledge, the present copolymer is the first example of COC which simultaneously possesses high Tg and improved mechanical performance. The transparency of HBMN-derived COC was also investigated by using UV−vis measurement. The representative curves scanned from 400 to 800 nm are provided in Figure 4

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ASSOCIATED CONTENT

* Supporting Information S

1

H and 13 C NMR spectra for HBMN comonomer, DSC curves for ethylene/HBMN copolymers, the procedure for synthesis of sulfonated ethylene/HBMN copolymer, TGA curves for ethylene/HBMN copolymers, FT-IR spectra for ethylene/ HBMN copolymer and sulfonated ethylene/HBMN copolymer. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel +86-431-85262124; Fax +86-431-85262039; e-mail ysli@ ciac.jl.cn. Notes

The authors declare no competing financial interest.

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Figure 4. Transmittance of HBMN-derived COC films (the film samples are put on the words): (A) HBMN mol % = 20.2%; (B) HBMN mol % = 30.4%.

ACKNOWLEDGMENTS The authors are grateful for subsidy provided by the National Natural Science Foundation of China (No. 20923003).

along with the corresponding film samples. It is found that the ethylene/HBMN copolymers are very transparent, and the transparency enhances with increasing the cyclic olefin incorporation (Figure 4, A vs B). For the copolymer with 30.4 mol % HBMN incorporation, the transmittance is higher than 90% (Figure 4, B).

REFERENCES

(1) (a) Li, X. F.; Hou, Z. M. Coord. Chem. Rev. 2008, 252, 1842− 1869. (b) Tritto, I.; Boggioni, L.; Ferro, D. R. Coord. Chem. Rev. 2006, 250, 212−241. (c) Kaminsky, W. Catal. Today 2000, 62, 23−34. (d) Kaminsky, W.; Arndt, M. Adv. Polym. Sci. 1997, 127, 143−187. (2) Recent progress: (a) Pan, L.; Liu, J. Y.; Ye, W. P.; Hong, M.; Li, Y. S. Macromolecules 2008, 41, 2981−2983. (b) Fujita, M.; Coates, G. W. Macromolecules 2002, 35, 9640−9647. (c) Lavoie, A. R.; Ho, M. H.; Waymouth, R. M. Chem. Commun. 2003, 864−865. (d) Liu, J. Y.; Nomura, K. Adv. Synth. Catal. 2007, 349, 2235−2240. (e) Wang, W.; Fujiki, M.; Nomura, K. J. Am. Chem. Soc. 2005, 127, 4582−4583. (f) Na, S. J.; Wu, C. J.; Yoo, J.; Kim, B. E.; Lee, B. Y. Macromolecules 2008, 41, 4055−4057. (g) Shiono, T.; Sugimoto, M.; Hasan, T.; Cai,

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CONCLUSIONS Novel COC has been successfully synthesized by effective copolymerization of ethylene and HBMN. This bulky cyclic olefin comonomer can be simply prepared in good yield via Diels−Alder reaction. Using CGC/Al(iBu)3/[Ph3C][B(C6F5)4] 5401

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dx.doi.org/10.1021/ma300730y | Macromolecules 2012, 45, 5397−5402