Polymerization of ethylene using a series of binuclear and a mononuclear Ni (II)-based catalysts

Article abstract of DOI:10.1002/pola.28186

A novel series of homo-, bi-, and mononuclear Ni(II)-based catalysts (BNC_n n = 1–4, MNC₄) were used for ethylene polymerization. The optimum conditions for the catalyst BNC₄ (the highest catalytic activity) was obtained at

Full text of DOI:10.1002/pola.28186

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Polymerization of Ethylene Using a Series of Binuclear
and a Mononuclear Ni (II)-Based Catalysts
Mostafa Khoshsefat,1 Gholam Hossein Zohuri,2 Navid Ramezanian,2
Saeid Ahmadjo,1 Meisam Haghpanah2
1Department of Catalyst, Iran Polymer and Petrochemical Institute (IPPI), Tehran, PO Box 14965/115, Iran
2Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, PO Box 91775, Iran
Correspondence to: G. H. Zohuri (E-mail: zohuri@um.ac.ir)
Received 1 April 2016; accepted 21 May 2016; published online 6 July 2016
DOI: 10.1002/pola.28186
ABSTRACT: A novel series of homo-, bi-, and mononuclear Ni(II)-
based catalysts (BNCn n 5 1–4, MNC4) were used for ethylene
polymerization. The optimum conditions for the catalyst BNC4
(the highest catalytic activity) was obtained at [Al]/[Ni]52000/1,
Tp 5 42 8C, and tp 5 20 min that was 1073 g PE/mmol Ni h. In theo-
retical study, steric and electronic effects of substituents and dii-
mine backbone led to prominent influence on the catalyst
behavior. The highest MV was resulted from polymerization using
BNC4; however, the highest unsaturation content was obtained
from BNC1. GPC analysis showed a broad MWD (PDI5 17.8).
BNC1 and BNC2 in similar structures showed broad peaks in DSC
thermogram, while BNC3 and BNC4 with more electronic effects
showed a peak along with a wide shoulder. Monomer pressure
increasing showed enhancing in activity of the BNC4, meanwhile
a peak with shoulder to a single peak in DSC thermogram and
uniformity in morphology of the resulted polymer were observed.
C
V
2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.
2016, 54, 3000–3011
KEYWORDS: branch; binuclear nickel complex; catalysts; a-dii-
mine catalyst; FTIR; late transition metal catalysts; polyethylene
(PE); structural study
considered as being one of the interesting research fields in
mono and multinuclear catalyst of the olefin polymerization
due to their unique reactivity patterns and unusual catalytic
properties such as producing branched polyethylene (PE)
without any a-olefin comonomers and chemical stability due
to less oxophilic properties.34–40 Furthermore, the key fea-
ture of these catalysts is the symmetrical and unsymmetrical
presence of ligands which effectively affect these catalysts
behavior.41,42 All this variety in structures can enhance by
homo and heterometallic centers. In the most of these cata-
lysts, presence of chelate ligands with aromatic rings cause
increasing in thermal stability, performance and more steric
and electronic effects.43,44 There is some binuclear structure
of diimine catalysts in Scheme 1 which are related to our
work. Catalysts a and b were activated with methylaluminox-
ane (MAO) and produced PE oligomers and waxes with
broad MWDs. Catalysts c, d, and e showed higher catalytic
activities, producing higher molecular weight PE with higher
degree of branching in comparison to mononuclear analo-
gous.26,45–48 Besides of all practical experiments, many
articles about theoretical study on structures of the catalysts
have been published. These studies can help researchers to
better judge on the structures, mechanisms, performances
INTRODUCTION Multinuclear catalysts are a class of multisite
catalysts which can be multi- or monometallic center. During
last decades, multinuclear catalysts have seen impressive
progress.1–7 Albeit mechanisms of these types of catalysts
are still in ambiguous due to complexity of theirs function
through the polymerization; however, there is two main sup-
posed structure include cooperation and independent effect
of active centers. Distance between the active centers and
the presence of weakly basic substituents are two important
factors that can control the cooperative effect of metal centers
in olefin homo- and copolymerization of polar monomers,
especially.8–15 According to the literatures, multinuclear cata-
lysts have shown various results in comparison to correspond
mononuclear catalysts such as both lower and higher catalyst
activity, bimodal to wide range molecular weights distribution,
isotacticity, and microstructures.16–23
There are several structures in multinuclear catalysts
containing metallocene and postmetallocene based and even
combination of them.24–28 The diversity of bridge between
the metal centers has given more variety to these types of
catalysts which can be rigid or flexible or even counter-ion
of cocatalyst.29–33 Homogenous late transition metal catalysts
Additional Supporting Information may be found in the online version of this article.
C
V
2016 Wiley Periodicals, Inc.
3000
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
SCHEME 1 Some Reported Binuclear Diimine Ni(II)-Based Complexes.
and are useful to predict the best and the most stable config-
uration of the complexes.49–53
diethyl ether (purity 99.5%) were supplied by Merck Chemi-
cal (Darmstadt, Germany) and used in synthesis of ligands
and catalysts. Decaline (decahydronaphthalene) (purity
97%), chlorobenzene, and calcium hydride were purchased
from Sigma Aldrich Chemicals (Steinheim, Germany). Triiso-
butylaluminum (purity 93%) was supplied by Sigma Aldrich
Chemicals (Steinheim, Germany) which was used in synthe-
sis of MAO according to the literature.54
In this study, a novel series of homometallic Ni (II)-based
binuclear catalysts (BNCn n 5 1–4) with different structures
and a mononuclear catalyst (MNC4) were synthesized. These
catalysts are used for polymerization of ethylene. Catalysts
behavior and properties of the produced polymers were
studied including dinuclearity effect such as synergistic and
asymmetric structure in higher catalytic activity, higher PE
molecular weight, branching, and broadening of MWD in
comparison to the mononuclear analogous. Theoretical study
on the structures of the catalysts was investigated and com-
pared with practical results.
Polymerization Procedure of Ethylene
The low-pressure polymerization process was carried out in
a round-bottom flask which was equipped with Schlenk sys-
tem, ethylene inlet, and magnetic stirrer, while the high-
pressure process (more than 2 bars) was carried out using a
1-L Buchi bmd 300-type stainless steel reactor.
EXPERIMENTAL
Characterization
1H NMR, 13C NMR, FTIR, and mass spectrums were recorded
using Bruker AVANCE III-300, Thermo Nicolet AVATAR 370
and Varian CH-7A spectrometers, respectively. Elemental
analysis was performed on a Thermo Finnigan Flash 1112EA
microanalyzer. Total spectra of all new compounds are pro-
vided in the Supporting Information. The viscosity average
molecular weight (Mv) of polymer samples was determined
according to the literature.55 Intrinsic viscosity [˛] was
measured in decaline at 133 6 1 8C using an Ubbelohde vis-
cometer. Mv values were calculated according to Mark-
Houwink equation, g 5 KMav (a 5 0.7, K 5 6.2 3 1024). Differ-
ential scanning calorimetry (DSC) instrument (Mettler Toledo
DSC822) with a rate of 10 8C/min instrument was used for
polymer characterization. SEM images and GPC curve were
resulted using LEO VP 1450 and Agilent PL-GPC220 instru-
ments, respectively.
Materials
All manipulations of air and/or water sensitive compounds
were conducted under argon or nitrogen atmosphere using
the standard Schlenk techniques. All the solvents were puri-
fied before use. Toluene (purity 99.9%) (Iran, Petrochemical)
was purified over sodium wire/benzophenone and used as
polymerization media. Dichloromethane (purity 96%) (Sigma
Aldrich Chemicals, Germany) and Methanol (Merck Chemical)
was purified over calcium hydride powder and distilled
before use in complex and ligand synthesis as solvent. Poly-
merization grade ethylene gas (purity 99.9%) (Iran, Petro-
chemical) was purified by passing through activated 4Å/13X
molecular sieves column. Aniline, 2,4,6-trimethyl aniline, 2,6-
diisopropyl aniline, 2,3-butanedione, 1,4-phenylene diamine,
acenaphthoquinone, nickel (II) bromide ethylene glycol
dimethyl ether complex [(DME) NiBr2] (purity 97%) and
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011
3001

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 2 Synthesis Procedure of Ligands and Catalysts.
Synthesis of Ligands and Catalysts
The procedure of ligands (SBLn n 5 1–5) and complexes
(BNCn n 5 1–4, MNC4) synthesis are depicted in Scheme 2.
The solution was stirred for 24 h. The ice bath was removed
and a solution of 1,4-diaminophenyl (2.8 mmol) in dichloro-
methane (5 mL) was added dropwise. The mixture was
stirred for another 24 h at room temperature. In both steps
of the ligand synthesis, the reaction progress and consump-
tion of the reactant was checked using TLC technique. The
solid precipitate was washed with cold methanol several
times, and the product was purified via column chromatogra-
phy [10% ethyl acetate (EA)/n-hexane-silica gel]. The solvent
was evaporated to afford the product with 60% yield.
Synthesis of SBL1 {2,4,6-trimethyl-C6H2-N 5 C(CH3)-
(CH3)C 5 N-C6H4-N 5 C(CH3)-(CH3)C 5 N-2,4,6-trimethyl-
C6H2}
To a stirred solution of diacetyl (5.3 mmol) and dichlorome-
thane (15 mL) in a round-bottom flask which was placed in
an ice bath, 2,4,6-trimethylaniline (5 mmol) was added drop-
wise in the presence of the catalytic amount of formic acid.
1H NMR (300 MHz, CDCl3, d, ppm): 1.2 (12H, s), 1.3 (6H, s),
2.1 (12H, s), 7.2 (4H, d), 7.3 (4H, s). 13C NMR (300 MHz,
CDCl3, selected resonances, d, ppm): 15.6, 16.4 (CH3-C 5 N),
168.2 (C 5 N), 18.1, 18.6 (CH3-Ar), 168.5 (C 5 N). MS (EI, m/
z): 478 [M1, 100%]. Anal. Calcd. for C32H38N4: C, 80.3; H,
8.0; N, 11.7. Found: C, 80.5; H, 7.9; N, 11.5. FTIR (KBr,
cm21): 1289 cm21 (-C-N-), 1636 cm21 (-C 5 N-).
Synthesis of SBL2 {2,6-diisopropyl-C6H2-N 5 C(CH3)-
(CH3)C 5 N-C6H4-N 5 C(CH3)-(CH3)C 5 N-2,6-diisopropyl-
C6H2}
The preparation of ligand SBL2 was similar to the method
used for SBL1 with 64% yield.
1H NMR (300 MHz, CDCl3, d, ppm): 1.2 (24H, d), 2.2 (12H,
s), 2.8 (4H, q), 6.9 (4H, d), 7.2 (2H, t), 7.3 (4H, d). 13C NMR
(300 MHz, CDCl3, selected resonances d, ppm): 15.7, 16.6
(CH3-C 5 N), 168.1 (C 5 N), 22.7, 23.2 (CH(CH3)2), 28.3, 28.5
(CH(Me)2), 168.3 (C 5 N). MS (EI, m/z): 562 [M1, 100%].
Anal. Calcd. for C38H50N4: C, 81.0; H, 9.0; N, 10.0. Found: C,
FIGURE 1 Clustered chart of BNCn n 5 1–4; activity versus [Al]/
[Ni], polymerization condition: monomer pressure 1.5 bar,
polymerization time 1 h, polymerization temperature 26 8C,
mmol BNCn5 4.2 3 1023 mmol, *trace.
3002
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
TABLE 1 Properties of the Resulted PE Using BNCn n 5 1–4
Amount
of Vinyl
Degree of
Branching
(in 1000 C)
Melting
DH melt
Crystallinity
(%)
Mv31024
Entry
Catalyst
Point (8C)
(Cal/g)
(g/mol)
(in 1000 C)
1
2
3
4
BNC1
BNC2
BNC3
BNC4
108.6
110.7
117.2
123.0
30.7
41.5
20.0
17.0
44.7
68.1
29.1
24.7
4.86
5.12
5.04
5.63
49.9
35.7
31.6
9.1
44
33
55
78
aPolymerization condition: [Al]/[Ni]51500/1, monomer pressure 1.5 bar, polymerization time 1 h, polymerization temperature 26 8C, mmol BNCn5 4.2
3 1023 mmol.
81.3; H, 8.8; N, 9.7. FTIR (KBr, cm21): 1207 cm21 (-C-N-),
100%]. Anal. Calcd. for C54H50N4: C, 85.9; H, 6.7; N, 7.4.
Found: C, 85.8; H, 6.4; N, 7.1. FTIR (KBr, cm21): 1274 cm21
(-C-N-), 1646 cm21 (-C 5 N-).
1637 cm21 (-C 5 N-).
Synthesis of SBL3 {2,4,6-trimethyl-C6H2-N 5 C-(C10H6)-
C 5 N-C6H4-N 5 C-(C10H6)-C 5 N-2,4,6-trimethyl-C6H2}
The preparation of ligand SBL3 was similar to the method
used for SBL1 with 59% yield.
Synthesis of SBL5 {2,6-diisopropyl-C6H2-N 5
C-(C10H6)-C 5 N-C6H5}
To the first step obtained product of ligand synthesis, a solu-
tion of aniline (5 mmol) in 10 mL dichloromethane was
added in the presence of formic acid as catalyst. The mixture
was stirred for 24 h at room temperature. In both steps of
the ligand synthesis, the reaction progress and consumption
of the reactant was checked using TLC technique. The solid
precipitate was washed with cold methanol several times
and the product was purified via column chromatography
[5% ethyl acetate (EA)/n-hexane-silica gel]. The solvent was
evaporated to afford the product with 53% yield.
1H NMR (300 MHz, CDCl3, d, ppm): 2.2 (12H, d), 2.4 (6H, s),
6.8 (4H, d), 7 (4H, s), 7.3 (4H, d), 7.4 (4H, t), 7.9 (4H, d). 13C
NMR (300 MHz, CDCl3, selected resonances d, ppm): 160.5
(C 5 N), 18.9, 19.2 (CH3-Ar), 160.9 (C 5 N). MS (EI, m/z):
672 [M1, 100%]. Anal. Calcd. for C48H38N4: C, 85.9; H, 5.7;
N, 8.8. Found: C, 85.7; H, 5.3; N, 8.8. FTIR (KBr, cm21):
1274 cm21 (-C-N-), 1646 cm21 (-C 5 N-).
Synthesis of SBL4 {2,6-diisopropyl-C6H2-N 5 C-(C10H6)-
C 5 N-C6H4-N 5 C-(C10H6)-C 5 N-2,6-diisopropyl-C6H2}
The preparation of ligand SBL4 was similar to the method
used for SBL1 with 64% yield.
1H NMR (300 MHz, CDCl3, d, ppm): 1.2 (12H, d), 2.7 (2H, q),
6.8 (2H, d), 6.9 (1H, t), 7.1 (2H, d), 7.2 (2H, t), 7.4 (1H, t),
7.7 (2H, t), 8.2 (2H, d), 8.3 (2H, d). 13C NMR (300 MHz,
CDCl3, selected resonances d, ppm): 161.1 (C 5 N), 24.9, 23.7
(CH(CH3)2), 29.1, 29.6 (CH(Me)2), 160.6 (C 5 N). MS (EI, m/
z): 416 [M1, 100%]. Anal. Calcd. for C54H50N4: C, 86.5; H,
6.8; N, 6.7. Found: C, 86.1; H, 6.6; N, 6.7. FTIR (KBr, cm21):
1276 cm21 (-C-N-), 1647 cm21 (-C 5 N-).
1H NMR (300 MHz, CDCl3, d, ppm): 1.2 (24H, d), 2.8 (4H, q),
2.1 (6H, s), 6.7 (4H, d), 7.3 (4H, d), 7.4 (2H, t), 7.9 (4H, t),
8.1 (4H, d), 8.3 (4H, d). 13C NMR (300 MHz, CDCl3, selected
resonances d, ppm): 161.3 (C 5 N), 24.3, 23.3 (CH(CH3)2),
29.4, 29.7 (CH(Me)2), 160.8 (C 5 N). MS (EI, m/z): 756 [M1,
FIGURE 2 DSC thermograms of the resulted PE using the BNCn
(n 5 1–4), polymerization condition: as mentioned in Table 1.
FIGURE 3 GPC curves of PE samples produced using BNC4
catalyst.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011
3003

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
TABLE 2 Selected Bond Distances (A˚), Bonding Angle (8), Planes Angle, Dipole Moment, Band Gap, Mullikan Charge, Thermal and
Free Energy of the BNCn n 5 1–4 and MNC4 Catalysts
Parameters
BNC1
BNC2
BNC3
BNC4
MNC4
a
NiABr1
2.40
2.41
2.41
2.42
2.42
2.40
2.05
2.04
1.27
4.21
3.62
4.16
3.38
105.65
81.13
124.36
122.43
31.23
–
b
NiABr2
2.44
2.44
2.41
2.41
c
NiAN1
2.03
2.03
2.33
2.34
d
NiAN2
2.01
2.01
1.94
1.94
C@N
1.27
1.27
1.26
1.26
e
NiAC1
4.31
4.28
4.25
4.25
f
NiAC2
3.35
3.48
4.22
4.27
g
NiAH1
3.39
3.40
3.71
3.64
h
NiAH2
3.09
3.08
3.70
3.76
Br1ANiABr2
NANiAN
104.23
79.6
103.66
79.3
141.85
81.2
137.91
80.9
i
NiANAC (Ps )
NiANAC (Pij)
121.27
120.41
37.52
38.51
58.19
145.6
8.30
120.86
120.58
26.49
5.43
130.43
119.88
10.14
3.24
131.33
119.71
1.97
P
P
P
P
s1-Pik
s2-Pil
20.18
78.95
173.46
8.61
s1-Ps2
E1-PE2
41.88
166.63
8.35
24.74
172.59
8.47
–
m
–
Dipole moment (Debye)
Band gap (eV)
18.04
0.30
0.94
–
0.31
0.31
0.34
0.31
Charge of Mulliken on M
0.94
0.98
0.99
1.00
0.95
0.96
0.98
0.96
Sum of electronic and
thermal energies (e.u.)
214,742.97
214,976.85
215,348.58
215,582.48
27906.49
Sum of electronic and
214,743.10
214,977.00
215,348.73
215,582.64
27906.58
thermal free energies (e.u.)
a
h
Br1: bromine atoms in front.
Br2: bromine atoms in behind.
H2: hydrogen atom on ortho-position of middle aryl ring (in behind).
Ps1: plane of the side aryl ring (right).
b
i
c
j
N1: nitrogen atoms connected to the side aryl ring.
Ps2: plane of the side aryl ring (left),
d
e
f
k
l
N2: nitrogen atoms connected to the middle aryl ring.
C1: carbon atom on ortho-position of side aryl ring (in front).
C2: carbon atom on ortho-position of side aryl ring (in behind).
H1: hydrogen atom on ortho-position of middle aryl ring (in front).
Pi: plane of the middle aryl ring.
PE1: plane of the diimine (right).
PE1: plane of the diimine (left).
m
g
SCHEME 3 Example of Conformers SBL2 Through Rotation Around C–N and C–C Bonds.
3004
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
SCHEME 4 Optimized Structure of Catalysts; BNC1 (A), BNC2 (B), BNC3 (C), BNC4 (D), MNC4 (E).
Synthesis of BNC1 Catalyst
The procedure of catalyst synthesis was conducted under
atmosphere of argon using the standard Schlenk techniques.
Into a solution of dimethoxyethanenickel dibromide (DME)
NiBr2 (0.14 mmol) in dichloromethane (10 mL), a solution of
Ligand SBL1 (0.062 mmol) in dichloromethane (5 mL) was
added dropwise. The mixture was stirred for 24 h at room
temperature. The precipitation product was filtered and
washed with Et2O for several times. The solid product was
collected after solvent evaporation. FTIR (KBr, cm21): the
imine signal was shifted to weak field as it coordinated to
the Ni atom; 1623 cm21 (-C 5 N-). Anal. Calcd. for
C32H38Br4N4Ni2: C, 42.0; H, 4.2; N, 6.1. Found: C, 41.7; H,
4.0; N, 5.6.
Synthesis of BNC2 Catalyst
The same method was employed for synthesis of BNC2 as
described in Synthesis of SBL3 {2,4,6-trimethyl-C6H2-N5C-
(C10H6)-C5N-C6H4-N5C-(C10H6)-C5N-2,4,6-trimethyl-C6H2} sec-
tion. FTIR (KBr, cm21): the imine signal was shifted to weak
field as it coordinated to the Ni atom; 1620 cm21 (-C 5 N-).
Anal. Calcd. for C38H50Br4N4Ni2: C, 45.6; H, 5.0; N, 5.6.
Found: C, 45.1; H, 4.6; N, 5.3.
FIGURE 4 FTIR spectrums of the resulted PE using the BNCn
n 5 1–4 catalysts.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011
3005

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 5 A redrawn mechanistic route for catalytic polymerization, propagation versus b-H elimination, and chain branching.75
[Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
Synthesis of BNC3 Catalyst
Synthesis of BNC4 Catalyst
The same method was employed for synthesis BNC3 as
described in Synthesis of SBL3 {2,4,6-trimethyl-C6H2-N5C-
(C10H6)-C5N-C6H4-N5C-(C10H6)-C5N-2,4,6-trimethyl-C6H2} sec-
tion. FTIR (KBr, cm21): the imine signal was shifted to weak
field as it coordinated to the Ni atom; 1624 cm21 (-C 5 N-).
Anal. Calcd. for C48H38Br4N4Ni2: C, 52.0; H, 3.5; N, 5.1.
Found: C, 51.4; H, 3.3; N, 4.7.
The same method was employed for synthesis BNC4 as
described in Synthesis of SBL3 {2,4,6-trimethyl-C6H2-N5C-
(C10H6)-C5N-C6H4-N5C-(C10H6)-C5N-2,4,6-trimethyl-C6H2} sec-
tion. FTIR (KBr, cm21): the imine signal was shifted to weak
field as it coordinated to the Ni atom; 1623 cm21 (-C 5 N-).
Anal. Calcd. for C54H50Br4N4Ni2: C, 54.4; H, 4.2; N, 4.7.
Found: C, 53.8; H, 4.0; N, 4.3.
Synthesis of MNC4 Catalyst
The same method was employed for synthesis BNC4 as
described in Synthesis of SBL3 {2,4,6-trimethyl-C6H2-N5C-
(C10H6)-C5N-C6H4-N5C-(C10H6)-C5N-2,4,6-trimethyl-C6H2} sec-
tion. FTIR (KBr, cm21): the imine signal was shifted to weak
field as it coordinated to the Ni atom; 1625 cm21 (-C 5 N-).
Anal. Calcd. for C54H50Br4N4Ni2: C, 55.7; H, 4.4; N, 4.4.
Found: C, 54.8; H, 4.3; N, 4.2.
TABLE 3 Polymerization of Ethylene Using the Catalyst BNC4
Time
(min)
Temperature
Yield
(g)
Activity (g PE/
mmol Ni h)
Run
(8C)
1
2
3
4
5
6
7
8
60
60
60
60
5
26
42
53
64
26
42
42
42
2.1
2.6
1.4
0.9
0.2
1.5
2.1
2.8
503.3
619.9
333.8
214.6
572.2
1,073.0
751.1
500.7
RESULTS AND DISCUSSION
To investigate the effect of structure especially ortho substit-
uent of the side aryl rings and adjacent group of diimines on
the catalyst behavior, ethylene polymerizations were carried
out using catalysts BNCn n 5 1–4 (Fig. 1) and MNC4.
20
40
80
MAO was used as cocatalyst. Initial investigation showed
that the catalyst BNC4 have the highest activity among the
Polymerization condition: [Al]/[Ni]52000/1, monomer pressure 1.5 bar,
mmol BNCn5 4.2 3 1023 mmol.
3006
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
TABLE 4 Polymerization of Ethylene Using the Catalyst BNC4
Pressure
(bar)
Yield
(g)
Activity (g PE/
mmol Ni h)
Melting
DHmelt
Crystallinity
(%)
Amount of
Branching
(in 1000 C)
Run
Point (8C)
(Cal/g)
Vinyl (in 1000 C)
1
2
3
4
0.75
1.5
3
1.1
2.6
3.1
4.5
262.3
619.9
739.2
1073.0
107.3
123.0
134.7
128.0
15.6
17.0
28.4
30.7
22.6
24.7
41.3
44.6
12.5
9.1
3.0
7.6
81
78
13
11
4.5
Polymerization condition: [Al]/[Ni] 5 2000/1, monomer pressure 1.5 bar, polymerization time 1 h, polymerization temperature 26 8C, mmol BNC45 4.2
3 1023 mmol.
four prepared binuclear catalysts that was 503.3 (g PE/
mmol Ni h) in studied range. While correspond mononuclear
BNC4 catalyst (MNC4) illustrated no activity in ethylene poly-
merization, Catalysts BNC1, BNC2, and BNC3 were capable to
polymerize ethylene with moderate activities (Fig. 1). Higher
activity of BNC4 denoted to the synergistic effect of dinu-
clearity and bulky group presence in comparison to no activ-
ity of MNC4.
PDI5 17.8 (Mw 5 33,632.7, Mn 5 1894.0) which can attribute
to difference in electronic environment around each active
center.
Theoretical study on the optimized structures (Scheme 4)
showed that there are more than one kind of active species
during the polymerization such as the presence of an asym-
metric centers which have impact on polymerization behav-
iors of the catalysts.25,39,58,59 Furthermore, a suggested
mechanism for the cooperative effect between the active cen-
ters can be considered as olefin or comonomer trapping
occurred.7,33 The highest viscosity average molecular weight
was belong to the polymer obtained using BNC4 catalyst. The
behavior may have attributed to the presence substituents of
aryl rings and adjacent diimine groups, which affect b-
hydrogen elimination and any chain transfer reactions.
Scheme 4 demonstrates ortho-positions with circles which
bulky diisopropyl substituents (B,D) blocks the axial coordi-
nation sites.38,60,61 Also bromine atoms in equatorial axis
position that shown in Scheme 4 which generate a center for
polymerization. Para substituents are characterized which
have influence on the catalyst activity, molecular weights and
extent of branching of polymer. The presence of methyl
group instead of hydrogen can cause decreasing in activities
and the average molecular weights of polymers.62–64 Absence
of the substituents in one side of MNC4, which has less elec-
tronic and steric effects around the metal center, can cause
decreasing in activity (E). In contrast, binuclears are more
active than MNC4 because of dinuclearity synergistic influ-
ence and more steric and electronic effects. Theoretical study
of structure of the complexes confirmed obtained results
from practical view of point (Table 2 and Scheme 4).
Hartree-Fock (hf) method with 6–31g** basis set (by Gaus-
sian 09W) was used to build up the structure and calculate
the parameters. Computation performed by considering the
possible conformers like foldamers (Scheme 3) and the most
stable ligand structure after nickel coordination.22,45,65
Results are depicted in the Scheme 4 and Table 2 including
optimized structures, bond distances, bond angels, dipole
moments, band gaps, Mullikan charges, sum of thermal,
free and electronic energies. As it demonstrates that struc-
ture of the complexes have effects on the position of the
atoms and the parameters, hindering and electronic impact
of the bulky substituents are obvious in the Scheme 4
which axis blocked and electron withdrawing in retarding
Polymer Characterizations
Thermal Properties
PE with the highest melting point was obtained using BNC4
catalyst (123 8C) which showed the highest Mv as well, while
the highest crystallinity (68.1%) was belong to the polymer
obtained using BNC2 catalyst (Table 1). The broad peaks in
DSC of the polymers obtained using BNC1, BNC2 catalysts,
and shoulders in BNC3 and BNC4 catalysts are related to the
various crystallinity areas in the PE (Fig. 2). This area is
resulted due to the polymerization in presence of the Ni (II)
diimine-based catalysts that produced branched PE and
binuclear type of these catalysts that increases this effect. To
clarify, the broadening transition has been attributed to a
sequence of melting followed by recrystallization steps of
less ordered domains with the variable degrees of chain
branching.56,57
Catalysts Structure and Polymer Properties
GPC analysis of the polymer obtained by BNC4 catalyst (Fig.
3) showed a broad distribution of molecular weight with
FIGURE 5 DSC thermograms of produced PE using BNC4, poly-
merization condition as mentioned in Table 4.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011
3007

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 6 SEM images of the PE in low pressure (1.5 bar).
b-hydrogen elimination and the olefin trapping can cause to
PE with higher branches. Scheme 5 shows a predicted mecha-
increasing of the activity and the average molecular weight.
nism of propagation, b-hydride elimination, and branching.
Depending on the catalyst structure, the termination of chain
growth occurred via b-H elimination, chain transfer to the
monomer, or chain transfer to the cocatalyst and branching
are due to reinsertion of vinyl-end chains (macro monomers)
so called chain-walking mechanism allowing the growing
center to migrate along the polymer chain.69–74 As stated
before, influence of structures and ligands on the polymer-
ization behaviors of complexes are depicted using these
circle signs.
Branching and Unsaturation Contents
As infrared spectrum of polymers illustrate in Figure 4,
bands at 1377–83 cm21 which assigned to the branching
content by comparison to quantity of CH3-end in HDPE (by
subtracting a reference spectrum of HDPE).66,67 To calcula-
tion vinyl amount in the PE, bands in the regions of 908 and
2019 cm21 belong to vinyl and CH2 groups were considered,
respectively.68 Unsaturation content in first sample (Entry 1)
that was obtained using the catalyst BNC1 is the highest one;
49.9 which shows more b-H elimination reaction (Scheme 5).
Lower electronic effects of substituents on the ortho-position
and adjacent diimine group which can cause to dissociation
of the chain along with vinyl-end. In contrast, the highest
degree of branching obtained by BNC4 catalyst with more
steric bulk and the highest hindering and electronic effects
which can cause to reinsertion of micromonomer and produced
Effect of Polymerization Conditions
Due to the high catalytic activity of the catalyst BNC4, further
studies have been focused on this catalyst. The effect of poly-
merization temperature and kinetics study of polymerization
on the catalyst behavior (Table 3) confirmed the fact that
polymerization temperature can enhance the catalyst per-
formance through increasing in the kinetic energy of
3008
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
FIGURE 7 SEM images of the PE in high pressure (4.5 bar).
molecules which facilitates transfer of the monomer to the
catalytic active centers and increasing alkylation reaction of
metal centers (until 42 8C).71 Polymerization temperature
higher than 42 8C can cause irreversible deactivation of the
active centers (chemical effect) and the reducing of solubility
of monomer in solvent as a physical function to reduce activ-
ity of the catalyst.72 Polymerization of ethylene in higher
temperatures meanwhile (53 and 64 8C) yielded a rubber-
like amorphous PE. Furthermore, the highest polymerization
activity was obtained after 20 min of polymerization. After-
ward, degradation and deactivation of active centers and
encapsulation of the centers by the polymer chain to the
metal which inhibit of insertion of monomer can cause to
decreasing in catalyst activity.52,60,61
some literatures higher pressure can cause reverse effect on
catalyst activity.41,72,77 DSC thermograms obtained from cata-
lyst BNC4 (Fig. 5) indicated some uniformity in the crystal-
linity of obtained polymer. Study of the PE morphology in
low and high pressure showed a uniformity in the morphol-
ogy of the polymer meanwhile polymerization activity
increased for catalyst BNC4 (Figs. 6 and 7).
CONCLUSIONS
Synthesis, characterization, practical and theoretical study on
structures and polymerization behaviors of a novel series of
bi-nuclear (BNCn n 5 1–4) and a mononuclear (MNC4) Ni(II)-
based catalysts in ethylene polymerization were presented.
The BNC4 catalyst showed the highest activity among the
binuclear catalysts and its analogues mononuclear complex.
Polymer architectures and catalyst activities were depending
on the structures of the catalysts such that presence of bulky
ortho-substituents on the side aryl rings and adjacent dii-
mine groups led to promoting the catalysts productivity,
increasing the viscosity average molecular weights, degree of
branching in obtained polymers and also theoretical study
confirmed these practical results. Furthermore, GPC and DSC
As monomer pressure increased, activity of the catalyst
BNC4 enhanced (Table 4) due to high concentration of the
monomer close to the catalyst active centers which led to
increasing of olefin trapping and reduction of branching
extent.61,74 The non-linear relationship between monomer
pressure and activity was reported in the literatures.75,76 In
studied range, a promoting in catalyst productivity was
obtained as monomer pressure increased, however, based on
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011
3009

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
23 P. Barbaro, C. Bianchini, G. Giambastiani, I. G. Rios, A. Meli,
W. Oberhauser, A. M. Segarra, L. Sorace, A. Toti. Organomet.
2007, 26, 4639.
analyses of resulted PEs in presence of BNC4 catalyst illus-
trated a broad MWD due to cooperative effect of centers and
a peak along with a shoulder in melting of crystallinity area
in DSC thermograms. Increasing in monomer pressure led to
more PE yield, uniformity, and regularity chain growth,
which confirmed by DSC thermogram and caused a uniform-
ity in SEM images.
24 Tomov, K. Kurtev. J. Mol. Catal. A: Chem. 1995, 103, 95–103.
25 C. Gorl, H. G. Alt. J. Organomet. Chem. 2007, 692, 5727–
5753.
26 H. K. Luo, H. Schumann. J. Mol. Catal. A: Chem. 2005, 227,
153–161.
27 B. K. Bahuleyan, U. Lee, C. S. Ha, I. Kim. Appl. Catal. A.
2008, 351, 36–44.
28 S. Xu, J. Huang. J. Appl. Polym. Sci. 2013, 130, 2891–2900.
ACKNOWLEDGMENTS
29 R. Chen, S. F. Mapolie. J. Mol. Catal. A: Chem. 2003, 193,
33–40.
The authors are thankful of Ferdowsi University of Mashhad
and Iran Polymer and Petrochemical Institute for all their
cooperation.
30 G. P. Abramo, L. Li, T. J. Marks. J. Am. Chem. Soc. 2002,
124, 13966–13967.
31 Jungling, S. Mulhaupt, R. H. Plenio. J. Organomet. Chem.
1993, 460, 191–195.
32 S. K. Noh, J. Kim, J. Jung, C. S. Ra, D. H. Lee, H. B. Lee, S.
W. Lee, W. S. Huh. J. Organomet. Chem. 1999, 580, 90–97.
REFERENCES AND NOTES
1 F. Lindenberg, T. Shribman, J. Sieler, E. Hey-Hawkins, M. S.
Eisen. J. Organomet. Chem. 1996, 51, 19–25.
33 L. Zhu, Z. S. Fu, H. J. Pan, W. Feng, C. Chen, Z. Q. Fan. Dal-
ton Trans. 2014, 43, 2900–2906.
€
2 H. G. Alt, R. Ernst, I. Bohmer. J. Mol. Catal. A: Chem. 2003,
191, 177–185.
34 B. K. Bahuleyan, K. J. Lee, S. H. Lee, Y. Liu, W. Zhou, I. Kim.
Catal. Today. 2011, 164, 80–87.
3 J. Schellenberg. Eur. Polym. J. 2004, 40, 2259–2267.
35 S. Damavandi, N. Samadieh, S. Ahmadjo, Z. Etemadinia, G.
H. Zohuri. Eur. Polym. J. 2015, 64, 118–125.
4 X. Li, X. Zhao, B. Zhu, F. Lin, J. Sun. Catal. Commun. 2007, 8,
2025–2031.
36 T. Hu, Y. G. Li, Y. S. Li, N. H. Hu. J. Mol. Catal. A: Chem.
2006, 253, 155–164.
5 R. Malgas, S. F. Mapolie, S. O. Ojwach, G. S. Smith. J. Orga-
nomet. Chem. 2008, 693, 2279–2286.
37 M. Jeon, C. J. Han, S. Y. Kim. Macromol. Res. 2006, 14,
306–311.
6 H. Jiang, F. He, J. Lu, Y. Xing. J. Mol. Catal. A: Chem. 2013,
380, 139–143.
38 D. P. Gates, S. A. Svejda, E. Onate, C. M. Killian, L. K.
Johnson, P. S. White, M. Brookhart. Macromolecules 2000, 33,
2320–2334.
7 H. K. Luo, C. Wang, W. Rusli, C. Zh. Li, E. Widjaja, P. K.
Wong, L. P. Stubbs, M. V. Meurs. J. Organomet. Chem. 2015,
798, 354–366.
39 H. Zou, F. M. Zhu, Q. Wu, J. Y. Ai, S. A. Lin. J. Polym. Sci.,
Part A: Polym. Chem. 2005, 43, 1325–1330.
8 M. R. Salata, T. J. Marks. Macromol. 2009, 42, 1920–1933.
40 Z. Ma, W. H. Sun, Z. L. Li, C. X. Shao, Y. L. Hu, X. H. Li.
Polym. Int. 2002, 51, 994–997.
9 S. Liu, A. Motta, A. R. Mouat, M. Delferro, T. J. Marks. J. Am.
Chem. Soc. 2014, 136, 10460–10469.
41 L. C. Simon, C. P. Williams, J. B. P. Soares, R. F. de Souza.
J. Mol. Catal. A: Chem. 2001, 165, 55–66.
10 J. P. McInnis, M. Delferro, T. J. Marks. Acc. Chem. Res.
2014, 47, 2545–2557.
42 S. Dridi, A. Mechria, M. Msaddek. J. Organomet. Chem.
2014, 772, 217–221.
11 S. Sujith, D. J. Joe, S. J. Na, Y. Wh. Park, C. H. Choi, B. Y.
Lee. Macromol. 2005, 38, 10027–10033.
43 J. L. Rhinehart, L. A. Brown, B. K. Long. J. Am. Chem. Soc.
2013, 135, 16316–16319.
12 S. B. Amin, T. J. Marks. J. Am. Chem. Soc. 2007, 129, 2938–
2953.
44 S. Dai, X. Sui, C. Chen. Angew.Chem. Int. Ed. 2015, 54,
9948–9953.
13 L. Guo, C. Chen. Sci. China. Chem. 2015, 58, 1663–1673.
14 R. Wang, X. Sui, W. Pang, C. Chen. Chem. Cat. Chem. 2016,
8, 434–440.
45 J. D. A. Pelletier, J. Fawcett, K. Singh, G. A. Solan. J. Orga-
nomet. Chem. 2008, 693, 2723–2731.
15 S. Takano, D. Takeuchi, K. Osakada, N. Akamatsu, A.
Shishido. Angew. Chem. Int. Ed. 2014, 53, 9246–9250.
46 Y. D. M. Champouret, J. Fawcett, W. J. Nodes, K. Singh, G.
A. Solan. Inorg. Chem. 2006, 45, 9890–9900.
16 R. Malgas, S. F. Mapolie, S. O. Ojwach, G. S. Smith, J.
Darkwa. Catal. Commun. 2008, 9, 1612–1617.
47 S. Jie, D. Zhang, T. Zhang, W. H. Sun, J. Chen, Q. Ren, D.
Liu, G. Zheng, W. Chen. J. Organomet. Chem. 2005, 690, 1739–
1749.
17 T. X. Sun, Q. Wang, Z. Q. Fan. Polym. 2010, 51, 3091–3098.
18 S. K. Noh, G. G. Byun, C. S. Lee, D. Lee, K. B. Yoon, K. S.
Kang. J. Organomet. Chem. 1996, 518, 1–6.
48 S. Kong, K. Song, T. Liang, C. Y. Guo, W. H. Sun, C.
Redshaw. Dalton Trans. 2013, 42, 9176–9187.
19 J. C. Sierra, D. Huerlander, M. Hill, G. Kehr, G. Erker, R.
Frohlich. Chem. Eur. J. 2003, 9, 3618–3622.
49 S. S. Ivanchev, A. V. Yakimansky, N. I. Ivancheva, G. A.
Tolstikov, I. I. Oleinik. Eur. Polym. J. 2012, 48, 191–199.
20 J. Kuwabara, D. Takeuchi, K. Osakada. Organomet. 2005, 24,
2705–2712.
ꢀ
50 F. Maseras, A. Lledos, Catalysis by Metal Complexes, Com-
putational Modeling of Homogeneous Catalysis, The Key Steps
in Olefin Polymerization Catalyzed by Late Transition Metals,
A. Michalak, T. Ziegler 2002, Vol 25, pp. 57–78.
21 B. K. Bahuleyan, J. H. Kim, H. S. Seo, J. M. Oh, I. Y. Ahn, C.
S. Ha, D. W. Park, I. Kim. Catal. Lett. 2008, 126, 371–377.
22 S. P. Netalkar, S. Budagumpi, H. H. Abdallah, P. P. Netalkar,
K. Revankar. J. Mol. Struct. 2014, 1075, 559–565.
51 R. Sandaroos, S. Damavandi, A. Farhadipour. Macromol.
Chem. Phys. 2010, 211, 2339–2346.
3010
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
52 A. Motta, I. L. Fragala, T. J. Marks. J. Am. Chem. Soc. 2009,
131, 3974–3984.
66 U. Keßner. Thermorheology as a method to investigate the
branching structures of polyethylenes. Ph.D. Thesis, University
of Erlangen-Nuremberg, 2010.
53 N. Bahri-Laleh, M. Nekoomanesh-Haghighi, S. A.
Mirmohammadi. J. Organomet. Chem. 2012, 719, 74–79.
67 J. P. Blitz, D. C. McFaddin. J. Appl. Polym. Sci. 1994, 51, 13–
20.
54 S. A. Sangokoya. Preparation of Aluminoxanes. 1996, EP
0463555 B1.
68 W. Collins, J. Seelenbinder, F. Higgins. Determination of the
vinyl content of polyethylene resins, Agilent Technology Inc.
US, 2012.
55 S. M. M. Mortazavi, H. Jafarian, M. Ahmadi, S. Ahmadjo. J.
Therm. Anal. Calorim. 2016, 123, 1469–1478.
69 L. H. Shultz, D. J. Tempel, M. Brookhart. J. Am. Chem. Soc.
2001, 123, 11539–11555.
56 Z. Guan, C. S. Popeney. Top Organomet. Chem. 2009, 24,
179–220.
70 G. H. Zohuri, R. Sandaroos, A. Mohammadi, S. M. Seyedi,
S. Damavandi. Letter 2010, 140, 160–166.
57 M. Vatankhah-Varnoosfaderani, S. Pourmahdian, F. Afshar-
Taromi. Iran. Polym. J. 2011, 20, 897–912.
71 H. Pourtaghi-Zahed, G. H. Zohuri. Polym. Bull. 2013, 70,
1769–1780.
58 M. Delferro, T. J. Marks. Chem. Rev. 2011, 111, 2450–2457.
59 H. Zou, S. Hu, H. Huang, F. Zhu, Q. Wu. Eur. Polym. J. 2007,
43, 3882–3891.
72 H. Jiang, J. Lu, F. Wang. Polym. Bull. 2010, 65, 767–777.
73 D. Santos, R. F. D. Souza. Polym. Bull. 2008, 60, 237–242.
60 M. Helldorfer, J. Backhaus, W. Milius, H. G. Alt. J. Mol.
Catal. A: Chem. 2003, 193, 59–70.
74 L. Guo, S. Dai, X. Sui, C. Chen. ACS Catal. 2016, 6, 428–
441.
61 F. Alobaidi, Z. Ye, S. Zhu. Polymer 2004, 45, 6823–6829.
62 J. Liu, Y. Li, N. Hu. J. Appl. Polym. Sci. 2008, 109, 700–707.
75 G. H. Zohuri, S. Damavandi, S. Ahmadjo, R. Sandaroos, M.
A. Shamekhi. poj. 2014, 1, 25–32.
63 J. Yuan, X. Wang, T. Mei, Y. Liu, C. Miao, X. Xie. Transit.
Metal. Chem. 2011, 36, 433–439.
76 H. Arabi, M. S. Beheshti, M. Yousefi, N. Ghasemi Hamedani,
M. Ghafelebashi. Polym. Bull. 2013, 70, 2765–2781.
64 C. S. Popeney, Z. Guan. Macromolecules 2010, 43, 4091–4097.
77 M. D. Leatherman, S. A. Svejda, L. K. Johnson, M.
Brookhart. J. Am. Chem. Soc. 2003, 125, 3068–3081.
65 I. Saraogi, A. D. Hamilton. Chem. Soc. Rev. 2009, 38, 1726–
1743.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 3000–3011
3011