Norbornene/ n -Butyl methacrylate copolymerization over α-Diimine nickel and palladium catalysts supported on multiwalled carbon nanotubes

Norbornene/n-Butyl Methacrylate Copolymerization over a-Diimine Nickel

and Palladium Catalysts Supported on Multiwalled Carbon Nanotubes

Ping Huo,1,2 Wanyun Liu,1,2 Xiaohui He,1 Yiwang Chen1

1Department of Chemistry/Institute of Polymers, Nanchang University, Nanchang 330031, China2Key Laboratory of Jiangxi University for Applied Chemistry and Chemical Biology, Yichun University, Yichun 336000, China

Correspondence to: Y. Chen (E-mail: [email protected]) or X. He (E-mail: [email protected])

Received 9 June 2014; accepted 16 August 2014; published online 8 September 2014

DOI: 10.1002/pola.27384

ABSTRACT: The covalently immobilized multiwalled carbon

nanotubes (MWNTs) supported three-dimensional geometry a-

diimine nickel, palladium catalysts are prepared by correspond-

ing a-diimine nickel, palladium complexes and activated

MWNTs. The molecular structures of the catalysts have been

confirmed by X-ray single-crystal analyses, NMR and XPS, as

well as elemental analysis. Compared with nickel, palladium

catalysts without modification and physical mixing of nickel,

palladium catalysts with MWNTs, the MWNTs supported

nickel, palladium catalysts show improved activity and produc-

tivity in norbornene homopolymerization and copolymerization

with polar monomer. The morphology of the resulting poly-

mers obtained from MWNTs-supported nickel(II) complex

reveals that the MWNTs are dispersed uniformly in polymer

and wrapped by polymers to squeeze out of spherical particles,

leading to the enhanced processability and mechanical proper-

ties. VC 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A:

Polym. Chem. 2014, 52, 3213–3220

KEYWORDS: addition polymerization; catalysts; mechanical

properties; morphology; multiwalled carbon nanotubes; sup-

ported catalyst

INTRODUCTION Addition polymers of norbornene (NB)-typemonomers exhibit a combination of properties that makethem ideal for many electronic and optical applications.1–4

These properties include a very high glass transition tempera-ture, high optical transparency, and low dielectric constant.However, these polymers suffer the biggest weakness in brit-tleness. To overcoming the weakness, a series of copolymers ofNB and polar monomers have been studied.5–7 However, dueto the catalyst poisoning in the direct copolymerization of NBand polar monomers, the simple and efficient synthesis ofwell-defined catalysts, which show an increased stability topolar monomers remains a scientific challenge. As we know,using heterogeneous supported catalyst is the most effectivemethod to increase stability of active center. Meanwhile, intro-ducing the supports into the polynorbornene material canimprove its some properties, such as the processability andmechanical properties.8 Therefore, it is very necessary todevelop new heterogeneous catalytic systems for the prepara-tion of polynorbornene. At present, much of the work isfocused on the researching and development of homogeneouscatalysts,9–15 the research of heterogeneous catalysts are stillrare. Actually, the advantages of heterogeneous catalysts can-not be neglected, such as, mild reaction, highly activation andthe controlling of the polymer morphology and properties.

Brookhart et al. show that covalent bonding between diiminenickel (Ni) catalysts and supports permits the use of activatorsother than MAO and allows higher Ni(II) loading on the sup-ports, leading to high activity. Through chemical bond, the cat-alyst is firmly immobilized on the supports surface,minimizing catalyst leaching, and reactor fouling.16 It has beensuggested that chemical and physical effect of supported cata-lysts may lead to high catalyst activity and productivity.17

It is well known that homogeneous catalysts have been suc-cessfully supported using various methods on many differenttypes carriers in olefin polymerization.18–21 For example, inor-ganic supports,22–24 polymeric supports,25–27 and nanostruc-tured materials.28,29 Nanostructured materials arecharacterized by their big surface area, mass transfer, andcontrolling of polymer properties and therefore have attractedmuch attention.30,31 They are used wildly as a carrier sup-ported homogeneous catalysts to show unexpected catalyticactivity in olefin polymerization.17 Among the nanostructuredmaterials, multiwalled carbon nanotubes (MWNTs) haveunique layered hollow structure, high aspect ratios of 1000 ormore, and high Young’s moduli in the range of 100–1250GPa,32–35 which make it an ideal carrier. It is anticipated thatthe MWNTs covalent on the homogeneous catalysts canincrease their stability and activities. The combination of

Additional Supporting Information may be found in the online version of this article.

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mechanical, electrical, and thermal transport properties ofMWNTs enables the obtaining of advance multifunctionalcomposite materials by the incorporation of nanotubes in var-ious polymer matrices.36,37

Compared with conventional catalysts, the catalysts withthree-dimensional (3D) geometry on the backbone displayedhigh catalytic activity and productivity.38 Herein, 3D geome-try 9,10-dihydro-9,10-ethanoanthracene-11,12-diimine nick-el(II), palladium(II) complexes are synthesized and covalentimmobilized onto MWNTs. Toward NB polymerization, theactivities of the following catalyst systems: nickel, palladiumcatalysts without modification, physical mixing of nickel, pal-ladium catalysts with MWNTs and the MWNTs supportednickel, palladium catalysts are investigated systematically.The morphology and mechanical properties of obtained poly-mers by the above three catalyst systems are also discussed.

EXPERIMENTAL

General MethodAll the reactions were performed under an atmosphere ofdry and oxygen-free argon using standard vacuum, Schlenk,or under nitrogen atmosphere in glove box (M Braun).

Short-hydroxylate MWNTs (purity �95%, outside diameter<8 nm, length: 0.5–2 mm) were purchased from NanjingXFNANO materials Tech, China (trade name of product isXFM 05). MWNTs were washed repeatedly with deionizedwater, dried in vacuum, and then stored in argon atmos-phere. NB was purchased from Alfa Aesar and purifiedthrough drying by sodium and distilled under dry nitrogen,then made a solution (0.5 g/mL) in toluene. n-Butyl methac-rylate was purchased from Aldrich and purified by anhy-drous magnesium sulfate. Other commercially availablereagents were purchased and used without purification.

The intensity data of the single crystals were collected on theCCD-Bruker Smart APEX II system. The nuclear magnetic reso-nance (NMR) spectra were collected on a Bruker ARX 600 NMRspectrometer with deuterated chloroform as the solvent and tet-ramethylsilane (TMS, d 5 0) as the internal standard. Elementalanalyses (EA) were characterized by EA with Vario ElementarIII. The amount of metals loaded on MWNTs was determined byinductively coupled plasma-atomic emission spectrometry (ICP-AES, OPTIMA 5300DV). The X-ray photoelectron spectroscopy(XPS) was performed on Kratos AXIS Ultra, operating at 15 kVand 15 mA with an alumina target (Al K a, h m 5 1486.71 eV).Scanning electron microscopy (SEM) images were carried outon an environmental scanning electron microscope (FEI Quanta200). Transmission electron microscopy (TEM) observationswere carried out at 100 Kv on a JEOL 1200 EXII microscope.Samples for TEM measurements were dispersed in dichloroben-zene in an ultrasonic bath for 5 min, and then a drop of the dis-persed solution was deposited on a copper grid.

Synthesis of a-Diimine LigandUnder a nitrogen atmosphere, to a solution of 30 mmol of4-amino-b-phenethanol in 150 mL toluene, 10 mmol of

9,10-dihydro-9,10-ethanoanthracene-11,12-dione and a cata-lytic amount of concentrated sulfuric acid were added. Themixture was heated under reflux. The resulting water wasremoved as azeotropic mixture using a Dean-Stark appara-tus. After 24 h, the reaction mixture was cooled to roomtemperature and evaporated at reduced pressure. Theresidual solids were further purified by silica column chro-matography (v/v, 20/1, petroleum ether/ethyl acetate) andwere crystallized from the mixture of petroleum ether andethyl acetate to get ligand as yellow crystals in 86.1%yield. The a-diimine ligand (L) was characterized by EA,single-crystal X-ray diffraction analysis and 1H and 13CNMR spectroscopy.

Elem. Anal. (%), found: C, 81.29; H, 6.04; N, 5.97; calcd: C,81.33; H, 5.97; N, 5.93. 1H NMR (CDCl3, d, ppm): 2.04 (s,2H), 2.93 (m, 4H), 3.95 (m, 4H), 5.42 (s, 2H), 6.88 (d, 4H,J5 2 Hz), 7.23–7.31 (m, 8H), 7.48 (d, 4H, J5 5.6 Hz). 13CNMR (CDCl3, d, ppm): 38.75, 50.08, 63.56, 120.23, 124.92,128.33, 128.67, 129.85, 138.61, 148.42, 160.85.

Synthesis of (a-Diimine Ligand) Nickel DibromideComplex0.2 mmol a-diimine ligand (L) and 0.2 mmol Ni(DME)Br2(dimethoxyethane, DME) were added to a Schlenk tubetogether with 10 mL dried dichloromethane, the reactionmixture was then stirred for 8 h at room temperature and10 mL absolute hexane was added. The dark red powderwas obtained from the mixture of dichloromethane and hex-ane in 85% yield. Complex was characterized by EA and 1HNMR spectroscopy.

Elem. Anal. (%), found: C, 55.66; H, 4.15; N, 4.11; calcd: C,55.61; H, 4.08; N, 4.05. 1H NMR (CDCl3, d, ppm): 2.05 (s,2H), 2.96 (m, 4H), 3.97 (m, 4H), 5.45 (s, 2H), 6.89 (d, 4H,J5 2 Hz), 7.21–7.35 (m, 8H), 7.49 (d, 4H, J5 5.6Hz). 13CNMR (CDCl3, d, ppm): 38.81, 50.11, 63.59, 120.28, 124.96,128.38, 128.71, 129.89, 138.66, 148.52, 161.25.

Synthesis of (a-Diimine Ligand) Methyl PalladiumChloride Complex0.5 mmol a-diimine ligand (L) and 0.5 mmol Pd(COD)MeCl(1,5-cyclooctadiene, COD) were added to a Schlenk tubetogether with 20 mL dried dichloromethane, the reactionmixture was then stirred for 12 h at room temperature, thesolution was filtered through Celite, and 10 mL absolute hex-ane was added. The yellow crystal complex was crystallizedfrom the mixture of dichloromethane and hexane in 82%yield. Complex was characterized by EA, single-crystal X-raydiffraction analysis, and NMR spectroscopy.

Elem. Anal. (%), found: C, 63.02; H, 5.01; N, 4.41; calcd: C,62.96; H, 4.96; N, 4.45. 1H NMR (CDCl3, d, ppm): 0.43 (s,3H), 2.05 (s, 1H), 2.07 (s, 1H), 2.95 (m, 2H), 2.96 (m, 2H),3.97 (m, 2H), 3.99 (m, 2H), 5.41 (s, 1H), 5.43 (s, 1H), 6.89(d, 4H, J5 2Hz), 7.26–7.38 (m, 8H), 7.49 (d, 4H, J5 5.6Hz).13C NMR (CDCl3, d, ppm): 1.14, 40.12, 50.28, 64.4, 123.45,124.12, 126.34, 127.65, 128.8, 130.42, 132.56, 137.28,139.75, 142.34, 142.95, 167.55, 172.23.

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Preparation of MWNTs Mixed NiLBr2 or PdLMeCl(NiLBr2@MWNTs or PdLMeCl@MWNTs)0.033 mmol pretreated nickel dibromide (NiLBr2) or (a-dii-mine ligand) methyl palladium chloride (PdLMeCl) were dis-persed in dry toluene in a 100-mL beaker and ultrasonicatedfor 20 min. MWNTs (200 mg) were added to the suspensionwith ultrasound treatment for another 30 min to obtain auniform solution. The toluene phase was pumped off and thesolid was dried in vacuum at 45 �C.

Synthesis of Carrier MWNTs/Me3AlShort-hydroxylate MWNTs (2 g) were mixed with 20 mL ofdry toluene and 3 mL of 2 M Me3Al hexane solution wereadded. After 2 h, the dark solid was washed three timeswith toluene and once with hexane. The solid was dried invacuum at 45 �C.

Supporting of NiLBr2 or PdLMeCl on MWNTs/Me3Al(NiLBr2/MWNTs/Me3Al or PdLMeCl/MWNTs/Me3Al)MWNTs/Me3Al (200 mg) was mixed with a solution of40 mg NiLBr2 or 25 mg PdLMeCl in 20 mL toluene. After 2h, the toluene phase was pumped off. The dark solid waswashed three times with toluene and dried in vacuum at45 �C.

Polymerization of Norbornene and n-Butyl MethacrylateA typical procedure was as follows: The appropriateB(C6F5)3 solid was introduced into the 100-mL two-neckedround-bottomed flask, then a certain amount of toluene solu-tion of NB, n-butyl methacrylate (n-BMA), and appropriateamount of catalyst were syringed into the well-stirred solu-tion in order, and the reaction was continuously stirred for

an appropriate period at the polymerization temperature.The polymerization was stopped by addition of acidic etha-nol (90:10 ethanol/HCl) and stayed overnight. The polymerswere then obtained through filtration or centrifugation andwashed by ethanol several times and were dried at 37 �C toa constant weight.

RESULTS AND DISCUSSION

Synthesis of Complexes NiLBr2 and PdLMeClThe stoichiometric condensation reaction of 9,10-dihydro-9,10-ethanoanthracene-11,12-dione and 4-amino-b-phenethanol pro-duced a-diimine ligand L (Scheme 1). Novel synthesizeda-diimine ligand formed NiLBr2 or PdLMeCl complexes ingood yields (Scheme 1) on reaction with Ni(DME)Br2(DME5 dimethoxyethane) or Pd(COD)MeCl in dichlorome-thane. Fortunately, crystals of the ligand and complexPdLMeCl suitable for single crystal X-ray diffraction analysiswere obtained by slow evaporation from dichloromethanesolution. However, the crystal quality of ligand and complexPdLMeCl were poor due to the partial evaporation of thesolvated molecules. The molecular structures of the ligandand complex PdLMeCl were shown in Supporting Informa-tion Figure S1 and Figure 1. In the case of the complexNiLBr2, due to its low solubility in dichloromethane, thecrystal structure could not be obtained and its structurewas determined by EA and NMR spectroscopy.

Synthesis of NiLBr2/MWNTs/Me3Al and PdLMeCl/MWNTs/Me3AlThe synthetic routes of the supported catalysts were shownin Scheme 1. Supporting Information Figure S2 displayed

SCHEME 1 Synthesis of MWNTs-supported catalysts.



XPS survey spectra of precatalyst NiLBr2/MWNTs/Me3Al.The peaks at binding energy (BE) were about 285, 400, 74.7,856, 68.4, and 532eV, which were attributed to C 1s, N 1s,Al 2p, Ni 2p3, Br 3d5, O 1s. The surface atoms contents(atom %) of C 1s, N 1s, Al 2p, Ni 2p3, Br 3d5 and O 1s,obtained by the area of the relevant bands in the high-resolution spectrum were 82.42, 0.39, 1.07, 0.12, 0.49 and15.6. Supporting Information Figure S3 displayed XPS surveyspectra of PdLMeCl/MWNTs/Me3Al precatalyst. The peaks atBE were about 285, 400, 74.8, 200, 338, and 533eV, whichwere attributed to C 1s, N 1s, Al 2p, Cl 2p, Pd 3d5, and O 1s.The surface atoms contents (atom %) of C 1s, N 1s, Al 2p, Cl2p, Pd 3d5, and O 1s, obtained by the area of the relevantbands in the high-resolution spectrum were 87.14, 0.23,1.54, 0.28, 0.16, and 10.38. The signals of C 1s and O 1swere very strong and corresponding to plenty of carbon andoxygen of carbon nanotubes surface. Moreover, the differentpeaks typically analyzed by Gaussian were resolved for thecomponents and the data were analyzed by looking at totalpeak ratios. The different components of Al 2p photoelectronpeaks were shown in Figure 2. Peaks at 74.7 and 75.3 ev foraluminum different chemical environment corresponded toO-Al-CH3 and O-Al-O, respectively. The presence of O-Al-Opeak was shown that NiLBr2 [Fig. 2(a)] and PdLMeCl [Fig.2(b)] had been successfully grafted to the MWNTs. Althoughthe total amount of Ni(II) or Pd(II) on the MWNTs shouldnot obtain from the XPS result because of the informationdepth. After calculated according to ICP-AES, the loadingNi(II) amount in supported catalyst NiLBr2/MWNTs/Me3Al is1.2 wt % and the loading Pd(II) amount in supported cata-lyst PdLMeCl/MWNTs/Me3Al is 2.1 wt %.

Evaluation of Supported Catalysts for NB PolymerizationNiLBr2, PdLMeCl, NiLBr2@MWNTs, PdLMeCl@MWNTs,NiLBr2/MWNTs/Me3Al, and PdLMeCl/MWNTs/Me3Al weretested as catalysts toward NB homopolymerization in thepresence of B(C6F5)3 and toluene as the reaction solvent(Table 1). All the complexes demonstrated high activities onthe order of (0.8–1.5) 3 106 gpolymer/ molmetal�h at 60 �Cwith B/catalyst ratio at 5/1. As we know, polymer yields andcatalytic activities were depended on the selected catalyst.Among these catalysts, the catalyst NiLBr2/MWNTs/Me3Al

had the highest activity, 1.5 3 106 gpolymer/molmetal�h. Com-parison with activities of these catalysts (NiLBr2 vs.PdLMeCl, NiLBr2@MWNTs vs. PdLMeCl@MWNTs, NiLBr2/MWNTs/Me3Al vs. PdLMeCl/MWNTs/Me3Al), it could be con-cluded that the activities of nickel catalysts were higher thanthat of palladium catalysts. NiLBr2@MWNTs andPdLMeCl@MWNTs with metal complex physical blend inMWNTs had the lowest activities, which was owing to quan-tity of hydroxy group on the surface of unactivated MWNTs.A comparison of these catalysts (NiLBr2/MWNTs/Me3Al vs.NiLBr2, PdLMeCl/MWNTs/Me3Al vs. PdLMeCl) demonstratedthat the activities of NiLBr2/MWNTs/Me3Al and PdLMeCl/MWNTs/ Me3Al were somewhat higher than that of theNiLBr2 and PdLMeCl. The reason was concluded that MWNTscould increase catalyst’s stability, make the active specie bet-ter contact with the NB monomer and not be wrapped bythe produced polymer at initial.

From Table 1, the NiLBr2/MWNTs/Me3Al showed the highestactivity with reaction time of 30 min. At the same tempera-ture and catalyst weight situation, the activity decreased con-stantly during polymerization time, but was stable comparedto homogeneous catalytic system, which was quite different

FIGURE 2 Al 2p-level spectra of NiLBr2/MWNTs/Me3Al (a) and

PdLMeCl/MWNTs/Me3Al (b). [Color figure can be viewed in the

online issue, which is available at wileyonlinelibrary.com.]

FIGURE 1 ORTEP plot of PdLMeCl showing the atom-labeling

scheme. Hydrogen atoms and some carbon atoms are omitted

for clarity. [Color figure can be viewed in the online issue,

which is available at wileyonlinelibrary.com.]


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from that observed with the homogeneous catalysts showingtypical decay-type kinetics.39 The activity decreased due toactive sites embedded in polymer particles growing up, butat the beginning, it was high activity because of larger sur-face area, better heat, and mass transfer. In addition to activ-ities, the big difference of these catalysts was polymer yield.NiLBr2/MWNTs/Me3Al and PdLMeCl/MWNTs/ Me3Al hadhigher polymer yield than other catalysts.

Since the activities and polymer yield of the above catalystssystems were different toward NB homopolymerization, aseries of Ni catalysts including NiLBr2, NiLBr2@MWNTs, andNiLBr2/MWNTs/Me3Al were selected as catalysts, to investi-gate the difference of activities and polymer yield towardcopolymerization of NB with n-butyl methacrylate (n-BMA).A series of copolymerizations of NB with n-BMA were inves-tigated with the catalyst system of Ni(II)/B(C6F5)3 in tolueneat 60 �C for 3 h under nitrogen atmosphere (Table 2). The n-BMA insertion ratio in copolymers could be controlled to be5.6–44.8 mol % at a content of 10–50 mol % of the n-BMA

in the monomer feed ratios by these catalysts systems. Theresults were presented in Table 2. The deactivation effectwith increasing n-BMA content in the feedstock compositionmay be caused by the coordination of ester-functional groupwith metal atom of catalyst. Compared with these catalysts,it could be observed that the catalytic activity and insertionratio of NiLBr2/MWNTs/Me3Al was higher than that ofNiLBr2 and NiLBr2@MWNTs at the same monomer feedratios due to the polar tolerate of the active species on thesupported increasing.

The copolymers were characterized by 1H NMR spectra (Fig.3). From 1H NMR, the characteristic peak at 3.8–3.9 ppmwas assigned to methane hydrogen corresponding to H30

that connect with ester group of n-BMA segment. The peakat 2.0–2.5 ppm could be attributed to methine hydrogen cor-responding to H2/H3, the peak at 1.7–2.0 ppm could beattributed to methine hydrogen corresponding to H1//H4,the peak at 0.8–1.0 ppm could be attributed to the methylhydrogen corresponding to H20/H60, and the peak at 0.9–1.7

TABLE 1 Norbornene Polymerization with Nickel, Palladium Catalystsa

No Catalyst Amount of Catalyst (mol) Reaction Time (h) Yield (%) Activityb

1 NiLBr2 5.0 3 1026 0.5 70.8 1.3

2 PdLMeCl 5.0 3 1026 0.5 47.0 0.9

3 NiLBr2@MWNTs 5.0 3 1026 0.5 59.6 1.1

4 PdLMeCl@MWNTs 5.0 3 1026 0.5 44.4 0.8

5 NiLBr2/MWNTs/Me3Al 6.1 3 1026 0.5 96.6 1.5

6 PdLMeCl/MWNTs/Me3Al 5.9 3 1026 0.5 68.6 1.1

7 NiLBr2/MWNTs/Me3Al 6.1 3 1026 0.1 16.7 1.3

8 NiLBr2/MWNTs/Me3Al 6.1 3 1026 0.3 55.4 1.4

9 NiLBr2/MWNTs/Me3Al 6.1 3 1026 1 98.2 0.8

11 NiLBr2/MWNTs/Me3Al 6.1 3 1026 2 98.8 0.4

a Conditions: cocatalyst was B(C6F5)3, B/catalyst (n/n) was 5/1,

NB5 0.05 mol, the heterogeneous catalyst (NiLBr2@MWNTs,

PdLMeCl@MWNTs, NiLBr2/MWNTs/ Me3Al, and PdLMeCl/MWNTs/ Me3Al):

30 mg, polymerization temperature was 60 �C, the solvent was toluene, the

total volume was 20 mL.b 106 g polymer (mol Cat.

21) h21.

TABLE 2 Copolymerization of NB and n-BMA Catalyzed by Nickel Catalystsa

No. Catalyst Amount of Catalyst (mol) NB/n-BMA (mol/mol) Yield (%) Activityb n-BMA (mol %)c

1 NiLBr2 5.0 3 1026 90/10 64.6 2.1 7.8

2 NiLBr2 5.0 3 1026 70/30 48.9 1.8 20.2

3 NiLBr2 5.0 3 1026 50/50 23.1 0.9 37.2

4 NiLBr2@MWNTs 5.0 3 1026 90/10 48.8 1.6 5.6

5 NiLBr2@MWNTs 5.0 3 1026 70/30 32.2 1.2 16.8

6 NiLBr2@MWNTs 5.0 3 1026 50/50 21.4 0.8 30.8

7 NiLBr2/MWNTs/Me3Al 6.1 3 1026 90/10 80.9 2.2 8.2

8 NiLBr2/MWNTs/Me3Al 6.1 3 1026 70/30 67.1 2.0 26.7

9 NiLBr2/MWNTs/Me3Al 6.1 3 1026 50/50 51.6 1.7 44.8

a Conditions: cocatalyst is B(C6F5)3, B/catalyst (n/n) is 5/1, nNB 1 nn-

BMA 5 0.05 mol, the heterogeneous catalyst (NiLBr2@MWNTs and

NiLBr2/MWNTs/Me3Al):30 mg, polymerization temperature is 60 �C, the

solvent is toluene, the total volume is 20 mL, reaction time is 3 h.

b 105 g polymer (mol Cat.21) h21.

c Determined by 1H NMR spectroscopy in CDCl3.



ppm could be attributed to methine hydrogen correspondingto H5/H6/H7/H10/H40/H50.

Polymer MorphologyFigure 4 showed the SEM images of copolymers with the 9:1feed ratio of NB/n-BMA obtained by different Ni catalysts.We could find that the morphology of polymer particledepended strongly on the catalyst. The morphology of thepolymer [Fig. 4(a)] obtained by NiLBr2 had crack in smoothplane. In Figure 4(b), MWNTs were difficult to disperse uni-formly in polymer obtained by NiLBr2@MWNTs and largeagglomerates were observed. The reason was attributed tothe weak interactions between MWNTs and copolymers. Dif-ferent from the above two images, a large number of dis-persed uniformly spherical particles in the polymersobtained by NiLBr2/MWNTs/Me3Al could be found in Figure4(c), and there was not found MWNTs on the surface ofpolymers. The reason was probably that the MWNTs werewrapped by polymers to squeeze out of spherical particles.

To further observe the internal structures of polymers, Fig-ure 5 presented the TEM images of copolymers with the 9:1feed ratio of NB/n-BMA sufficiently purified by hot vacuumfiltration. From the surface of the copolymers obtained byNiLBr2@MWNTs [Fig. 5(a)], the surface of MWNTs was rela-tively clean, indicating that most copolymers were not

adsorbed on the surface of MWNTs. On the contrary, in Fig-ure 5(b), the MWNTs were wrapped by polymers obtainedby NiLBr2/MWNTs/Me3Al to squeeze out of spherical par-ticles and were dispersed uniformly in polymer. The uniformpolymer morphology demonstrated that there was no frag-mentation process; the growth of polymer took place fromthe active sites evenly distributed on the surface of catalystparticle. Meanwhile, the active catalyst centers remainedwithin the same polymer particle without leaching from thesupported catalyst. However, the nickel complex was notsupported on the surface of MWNTs uniformly throughchemical bond process, which leaded to the obtained poly-mer spherical particles were irregular. The thickness of thecopolymer layer on the surface of MWNTs ranged from 3 to7 nm.

Mechanical Properties of the PolymersIn an attempt to examine the effect of various catalyststoward copolymers’ mechanical properties, the tensile testsof copolymers with the 9:1 feed ratio of NB/n-BMA compo-sites were measured by dynamic thermomechanical analysis(DMA) in Figure 6. The copolymers films by NiLBr2 couldnot be obtained because of their brittleness. Other carbonnanotubes hybrid copolymers films obtained byNiLBr2@MWNTs and NiLBr2/MWNTs/Me3Al had goodmechanical properties instead of brittleness. The reason ofphenomenon was that introducing carbon nanotubes intopolymers could make the polymers flexible and improvetheir processability. The copolymer film obtained by NiLBr2/MWNTs/Me3Al showed best mechanical properties, the

FIGURE 3 1H NMR spectra of copolymers with the 9:1 feed

ratio of NB/n-BMA obtained by (a) NiLBr2, (b) NiLBr2@MWNTs,

and (c) NiLBr2/MWNTs/Me3Al. [Color figure can be viewed in

the online issue, which is available at wileyonlinelibrary.com.]

FIGURE 4 SEM images of copolymers with the 9:1 feed ratio of NB/n-BMA obtained by (a) NiLBr2, (b) NiLBr2@MWNTs, and (c)

NiLBr2/MWNTs/Me3Al.

FIGURE 5 TEM images of copolymers with the 9:1 feed ratio of

NB/n-BMA obtained by (a) NiLBr2@MWNTs and (b) NiLBr2/

MWNTs/Me3Al. [Color figure can be viewed in the online issue,

which is available at wileyonlinelibrary.com.]


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tensile strength, which could be 7.7 MPa, and the elastic modu-lus, which could be as high as 957 MPa. The increase in elasticmodulus and tensile strength of copolymers obtained by car-bon nanotubes chemical bond catalysts indicated that theinteractions between copolymers and MWNTs were strongenough to allow a very efficient load transfer to MWNTs, pro-viding high mechanical strengths. Thus, it was demonstratedthat the carbon nanotubes were dispersed into the polymersprepared by MWNTs-supported metal catalysts uniformly,resulting in enhanced the polymers’ reinforcing effects.

CONCLUSIONS

The NiLBr2, PdLMeCl, NiLBr2@MWNTs, PdLMeCl@MWNTs,NiLBr2/MWNTs/ Me3Al, and PdLMeCl/MWNTs/Me3Al weresynthesized and characterized. Due to MWNTs’ big surfaceand good disperse in catalysts through chemical bond, theNiLBr2/MWNTs/Me3Al and PdLMeCl/MWNTs/Me3Al exhib-ited high activities and productivity in NB polymerization.The morphology and mechanical properties of obtained poly-mers by the above catalyst systems were investigated sys-temically for the first time. The carbon nanotubes wereuniformly dispersed in polymers obtained by NiLBr2/MWNTs/Me3Al and increased the mechanical properties ofpolymers. This work presented the example of introducingcarbon nanotubes as an effective reinforcement for the poly-mer composites into the polymers through MWNTschemical-supported metal catalysts.

ACKNOWLEDGMENT

This workwas supported by the National Natural Science Foun-dation of China (21164006).

REFERENCES AND NOTES

1 S. Martinez-Arranz, A. C. Albeniz, P. Espinet, Macromolecules

2010, 43, 7482–7487.

2 J. H. Park, C. Yun, M. H. Park, Y. Do, S. Yoo, M. H. Lee, Mac-

romolecules 2009, 42, 6840–6843.

3 S. Oh, J.-K. Lee, P. Theato, K. Char, Chem. Mater. 2008, 20,

6974–6984.

4 K. H. Park, R. J. Twieg, R. Ravikiran, L. F. Rhodes, R. A. Shick,

D. Yankelevich, A. Knoesen, Macromolecules 2004, 37, 5163–

5178.

5 A. Ravasio, L. Boggioni, I. Tritto, Macromolecules 2011, 44,

4180–4186.

6 E. Ihara, S. Honjyo, K. Kobayashi, S. Ishii, T. Itoh, K. Inoue, H.

Momose, M. Nodono, Polymer 2010, 51, 397–402.

7 T. Hasan, T. Ikeda, T. Shiono, J. Polym. Sci. Part A: Polym.

Chem. 2007, 45, 4581–4587.

8 B. Yuan, X. H. He, Y. W. Chen, K. T. Wang, Macromol. Chem.

Phys. 2011, 212, 2378–2388.

9 W. J. Zhang, W. H. Sun, C. Redshaw, Dalton Trans. 2013, 42,

8988–8997.

10 S. L. Kong, K. F. Song, T. L. Liang, C. Y. Guo, W. H. Sun, C.

Redshaw, Dalton Trans. 2013, 42, 9176–9187.

11 L. P. He, J. Y. Liu, Y. G. Li, S. R. Liu, Y. S. Li, Macromole-

cules 2009, 42, 8566–8570.

12 Y. L. Qiao, G. X. Jin, Organometallics 2013, 32, 1932–

1937.

13 H. D. Mkoyi, S. O. Ojwach, I. A. Guzei, J. Darkwa, J. Organo-

met. Chem. 2013, 724, 95–101.

14 Z. B. Guan, Chem. Eur. J. 2002, 8, 3086–3092.

15 X. H. He, Y. M. Liu, L. Chen, Y. W. Chen, D. F. Chen,

J. Polym. Sci. Part A: Polym. Chem. 2012, 50, 4695–4704.

16 P. Preishuber-Pflugl, M. Brookhart, Macromolecules 2002,

35, 6074–6076.

17 J. R. Severn, J. C. Chadwick, Dalton Trans. 2013, 42, 8979–

8987.

18 G. G. Hlatky, Chem. Rev. 2000, 100, 1347–1376.

19 G. Fink, B. Steinmetz, J. Zechlin, C. Przybyla, B. Tesche,

Chem. Rev. 2000, 100, 1377–1390.

20 F. Silveira, M. D. M. Alves, F. C. Stedile, S. B. Pergher, J. H.

Z. Santos, J. Mol. Catal. A Chem. 2010, 315, 213–220.

21 W. Li, A. Adams, J. Wang, B. Blumich, Y. Yang, Polymer

2010, 51, 4686–4697.

22 J. C. Hicks, B. A. Mullis, C. W. Jones, J. Am. Chem. Soc.

2007, 129, 8426–8427.

23 D. P. Allen, M. M. Van Wingerden, R. H. Grubbs, Org. Lett.

2009, 11, 1261–1264.

24 F. Blanc, C. Coperet, J. Thivolle-Cazat, J.-M. Basset, Angew.

Chem. Int. Ed. 2006, 45, 6201–6203.

25 B. Heurtefeu, C. Bouilhac, E. Cloutet, D. Taton, A. Deffieux,

H. Cramail, Prog. Polym. Sci. 2011, 36, 89–126.

26 J. Lu, P. H. Toy, Chem. Rev. 2009, 109, 815–838.

27 M. R. Buchmeiser, Chem. Rev. 2009, 109, 303–321.

28 E. L. Margelefsky, R. K. Zeidan, V. Dufaud, M. E. Davis, J.

Am. Chem. Soc. 2007, 129, 13691–13697.

29 L. A. Williams, T. J. Marks, ACS Catal. 2011, 1, 238–245.

30 A. T. Bell, Science 2003, 299, 1688–1691.

31 Z. Li, L. A. Fredin, P. Tewari, S. A. DiBenedetto, M. T.

Lanagan, M. A. Ratner, T. J. Marks, Chem. Mater. 2010, 22,

5154–5164.

32 M. F. Yu, O. Lourie, M. J. Dyer, K. Moloni, T. F. Kelley, R. S.

Ruoff, Science 2000, 287, 637–640.

33 M. F. Yu, B. S. Files, S. Arepall, R. S. Rouff, Phys. Rev. Lett.

2000, 84, 5552–5555.

FIGURE 6 Mechanical properties of copolymers with the 9:1

feed ratio of NB/n-BMA obtained by (a) NiLBr2@MWNTs and

(b) NiLBr2/MWNTs/Me3Al. [Color figure can be viewed in the

online issue, which is available at wileyonlinelibrary.com.]




34 A. Krishnan, E. Dujardin, T. W. Ebbesen, P. N. Yianilos, M.

M. J. Treacy, Phys. Rev. B 1998, 58, 14013–14019.

35 P. Poncharal, Z. L. Wang, D. Ugarte, W. A. de Heer, Science

1999, 283, 1513–1516.

36 P. M. Ajayan, J. Shur, N. Koratkar, J. Mater. Sci. 2006, 41,

7824–7829.

37 P. M. Ajayan, Chem. Rev. 1999, 99, 1787–1799.

38 P. Huo, W. Y. Liu, X. H. He, Z. H. Wei, Y. W. Chen, Polym.

Chem. 2014, 5, 1210–1218.

39 B. K. Bahuleyan, G. W. Son, D.-W. Park, C.-S. Ha, I.

Kim, J. Polym. Sci. Part A: Polym. Chem. 2008, 46, 1066–

1082.


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