Mono- and binuclear nickel catalysts for 1-hexene polymerization

Article abstract of DOI:10.1002/aoc.4355

Polymerization of 1-hexene was carried out using a mononuclear (MN) catalyst and two binuclear (BN₁ and BN₂) α-diimine Ni-based catalysts synthesized under controlled conditions. Ethylaluminium sesquichloride (EASC) was used as an ef

Full text of DOI:10.1002/aoc.4355

Received: 31 December 2017
DOI: 10.1002/aoc.4355
Revised: 20 February 2018
Accepted: 22 February 2018
F U L L P A P E R
Mono‐ and binuclear nickel catalysts for 1‐hexene
polymerization
1
1,2
1
Abbas Dechal | Mostafa Khoshsefat | Saeid Ahmadjo
|
1
3
4
Seyed Mohammad Mahdi Mortazavi | Gholam Hossein Zohuri
| Hossein Abedini
1
Department of Catalysis, Iran Polymer
Polymerization of 1‐hexene was carried out using a mononuclear (MN) catalyst
and two binuclear (BN and BN ) α‐diimine Ni‐based catalysts synthesized
and Petrochemical Institute (IPPI), PO
Box 14965/115, Tehran, Iran
1
2
2
Department of Chemical and Materials
under controlled conditions. Ethylaluminium sesquichloride (EASC) was used
Engineering, University of Alberta,
Edmonton, Alberta, Canada
as an efficient activator under various polymerization conditions. The highly
−
1
3
active BN catalyst (2372 g poly(1‐hexene) (PH) mmol cat) in comparison
Department of Chemistry, Faculty of
2
−
1
−1
Science, Ferdowsi University of Mashhad,
PO Box 91775, Mashhad, Iran
to BN (920 g PH mmol cat) and the MN catalyst (819 g PH mmol cat)
1
resulted in the highest viscosity‐average molecular weight (M ) of polymer.
v
4
Polymerization Engineering Department,
Moreover, the molecular weight distribution (MWD) of PH obtained using
Iran Polymer and Petrochemical Institute
(
IPPI), PO Box 14965/115, Tehran, Iran
BN
/EASC was slightly broader than those obtained using BN and MN (2.46
2 1
for BN versus 2.30 and 1.96 for BN and MN, respectively). These results,
2
1
Correspondence
Saeid Ahmadjo, Department of Catalysis,
Iran Polymer and Petrochemical Institute
along with the highest extent of chain walking for BN , were attributed to
2
steric, nuclearity and electronic effects of the catalyst structures which could
control the catalyst behaviour. Differential scanning calorimetry showed that
the glass transition temperatures of polymers were in the range − 58 to
(
IPPI), PO Box 14965/115, Tehran, Iran.
Email: s.ahmadjo@ippi.ac.ir
−
81 °C, and broad melting peaks below and above 0 °C were also observed.
In addition, longer α‐olefins (1‐octene and 1‐decene) were polymerized and
characterized, for which higher yield, conversion and molecular weight were
observed with a narrower MWD. The polymerization parameters such as
polymerization time and polymerization temperature showed a significant
influence on the productivity of the catalysts and M of samples.
v
KEYWORDS
binuclear, chain walking, cooperative effect, late transition metal, poly(1‐hexene)
1
| INTRODUCTION
strengths, low toxicity, appropriate fatigue properties,
good resistance to plasticizer migration and low cost have
Today, it is known that polyolefins play a significant role
in human life. The production of these polymers,
particularly highly branched polyolefins, is growing pro-
numerous applications as lubricants, adhesives, waxes
and oils, primers, drag‐reducing agents used in oil pipe-
[
4–8]
lines, electrical insulators, etc.
[1–3]
gressively.
For many applications, polyethylene, poly-
There are some reports on the polymerization of 1‐
[
9–17]
propylene and poly(α‐olefin)s with long‐chain branches
have significant features. For instance, poly(1‐hexene)
and poly(1‐octene) depending on their molecular weight
and due to their mechanical, thermal and chemical
hexene using various types of catalysts.
In this
regard, for example, the microstructure of poly(1‐hexene)
obtained using α‐diimine nickel catalysts was investi-
[
14]
gated by Sivaram and co‐workers,
and a polymer
Appl Organometal Chem. 2018;e4355.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
1 of 9
https://doi.org/10.1002/aoc.4355

2
of 9
DECHAL ET AL.
structure with methyl, butyl and long‐chain branches was
demonstrated. Moreover, Nakata et al. reported the syn-
thesis of poly(1‐hexene) with a narrow molecular weight
distribution (MWD) and high stereospecific index (95%)
using Hf‐based metallocene/methylaluminoxane catalytic
concentration have an influence on the polymer micro-
[
35–46]
structure.
In continuation of previous work,
[
44]
in the study
reported here we synthesized and characterized a new
binuclear catalyst and its mononuclear analogue and
employed them in the polymerization of 1‐hexene. The
behaviour of the catalysts and the physical properties of
the polymers such as average molecular weight, MWD,
branching density and branching distribution as well as
their thermal properties were investigated. The influences
of catalyst structure, cooperative effect and polymeriza-
tion conditions (monomer length, temperature, time
and concentration of co‐catalyst) on the polymer proper-
ties were also investigated.
[15]
system.
Our group has reported recently on high‐
molecular‐weight poly(1‐hexene) and its use in oil pipe-
[
8,16]
lines as a drag‐reducing agent.
Study of the backbone
[16]
of ligands of amine–imine nickel catalysts
indicated
that steric hindrance led to selectivity of 1,2‐insertion
along with chain walking, causing the production of
amorphous poly(1‐hexene), while
a
less crowded
structure on the backbone with 2,1‐insertion resulted in
[17]
semicrystalline
polyethylene.
Furthermore,
in
comparison to mononuclear catalysts, the cooperative
effect of binuclear palladium catalysts in polymerization
of 1‐hexene led to a low branching density level which
could be attributed to higher chain walking ability
2 | EXPERIMENTAL
2.1 | Materials
[18,19]
(straightening of chain).
Contrary to mononuclear
catalysts, the cooperative effect of multinuclear catalysts
in olefin polymerization has a significant influence on
the catalyst activity and microstructural features of
the resulting polymer such as branching density,
tacticity, molecular weight and unsaturation chain re‐
All manipulations of air−/water‐sensitive compounds
were conducted under Ar/N2 atmosphere using the
standard Schlenk technique. All solvents were purified
prior to use. Toluene from Iran Petrochemical Co.
(
99.9%) was purified over sodium wire/benzophenone,
[20–24]
insertion.
The distance between the centres and
and used as polymerization medium. Dichloromethane
the steric hindrance around the active sites are two main
(
(
96%, Sigma‐Aldrich Chemicals, Germany) and methanol
Merck Chemical Co.) as solvents were purified over
[25–27]
factors controlling the cooperative effect.
Moreover,
the presence of aromatic bridges in binuclear catalysts
leads to increasing thermal stability, and steric and
calcium hydride powder and distilled prior to use in the
synthesis of complex and ligand. Xylene was purchased
from Merck Chemical Co. 1‐Hexene, 1‐ocetene and 1‐
decene monomers were supplied by Mehr Petrochemical
Company (Iran). 2,6‐Diisopropylaniline, butanedione,
[25–29]
electronic effects.
Marks and co‐workers reported
that binuclear complexes bearing rigid structure and
proximate centres lead to higher productivities and methyl
[
25]
branch selectivity than their mononuclear analogues.
2,3,5,6‐tetramethyphenyldiamine, acenaphthoquinone,
The results, which were confirmed by one‐ and two‐
dimensional NMR observations, secondary agostic
interaction, binding of monomer to the adjacent Ni centre
and increasing high local concentration of monomer,
could be attributed to the presence of the second metal
nickel(ІІ) bromide ethylene glycol dimethyl ether
complex ((DME)NiBr ; 97%) and diethyl ether (99.5%)
2
were supplied by Merck Chemical Co. (Darmstadt,
Germany) and used in the synthesis of ligands and
catalysts. Ethylaluminium sesquichloride (EASC; 97%
purity) was supplied by Sigma‐Aldrich Chemicals
[
24–30]
centre, which, in turn, increased the chain walking.
Chen and co‐workers also claimed a lower branching
density for binuclear catalysts compared to mononuclear
catalysts, which could be explained by the interaction of
β‐hydrogen and the second metal centre through the
cooperative effect, which, in turn, increased the chain
(
Steinheim, Germany).
2.2 | Polymerization Procedure
[31]
walking.
The effect of catalyst structure and reaction
The polymerization of 1‐hexene, performed in a round‐
bottom flask, was carried out using a Schlenk system
before and during the injections. It should be noted that
1‐hexane monomer was purified prior to use. The mono-
mer (10 ml) was injected to the flask containing 6 ml of
solvent (toluene), and then the desired amounts of co‐
catalyst and catalyst were introduced into the flask. The
poly(1‐hexene) produced was precipitated and purified
using acidic methanol (5%).
conditions on the chain walking mechanism was
[32–34]
investigated by Guo et al.
For late transition metal
catalysts based on nickel and palladium, before the
second insertion of monomer, the reaction mechanism
includes β‐hydrogen elimination and an isomerization
[32]
process.
The symmetry in the chelating ligand
structure, steric hindrance and polymerization conditions
such as temperature, pressure and monomer

DECHAL ET AL.
3 of 9
2
.3 | Characterization
scanning calorimetry (DSC) thermograms were recorded
with a PerkinElmer DSC Q100 instrument.
1
13
H NMR, C NMR and Fourier transform infrared (FT‐
IR) spectra were obtained using Bruker AC‐300 and
Thermo Nicolet AVATAR 370 spectrometers. Elemental
and mass spectral analyses were performed with a
Thermo Finnigan Flash 1112EA microanalyser and a
Varian CH‐7A spectrometer. The branching density
and branching distribution of poly(1‐hexene) were cal-
2.4 | Preparation of Ligands and Catalysts
The ligands (SL, SL and SL ) and complexes (MN, BN
1
1
2
and BN ) were synthesized according to the procedure
2
presented in Scheme 1. Experimental details including
1
13
H NMR, CNMR, FT‐IR and mass spectra and elemen-
tal analyses of ligands (SL, SL and SL ) and complexes
[13,33,34]
culated according to the literature.
of 1‐hexene monomer, which can be accomplished by
The insertion
1
2
(
MN, BN1 and BN ) are provided in the supporting
2
1
,2‐ or 2,1‐insertion, was calculated according to equa-
information.
[17,47]
tion (1)
:
Br
2.4.1 | Ligand SL
%
2; 1 ¼ 166:7 − 1
(1)
66:7
The procedure used was that according to Khoshsefat
[
44]
1
et al.
Yield 91%. H NMR (300 MHz, CDCl , δ, ppm):
3
where Br is the total branching density. For poly(1‐octene)
and poly(1‐decene), the theoretical value (166.7) could be
replaced by 125 and 100, respectively.
1.0 (12H, d), 1.3 (12H, d), 3.1 (4H, sep), 6.8 (2H, d) 7.4
+
(
1
6H, m), 7.7 (2H, t), 8.3 (2H, d). MS (EI, m/z): 500 [M ,
00%]. Anal. Calcd for C H N (%): C, 86.35; H, 8.05;
36
40 2
Moreover, the 1,ω‐enchainment was calculated using
[47]
N, 5.59. Found (%): C, 86.18; H, 7.98; N, 5.65. FT‐IR
the following equation
:
−
1
(
KBr, cm ): 1271 (―C═N―), 1626 (―C═N―).
aB
1; ω ¼ 1000 − 1
%
þ 2B
(2)
000
2.4.2 | Ligand SL1
where a is the number of pendant monomers chains and
B is the overall branches. Intrinsic viscosity, η, was mea-
sured in toluene at room temperature using an
Ubbelohde viscometer. Viscosity‐average molecular
The procedure used was that according to Khoshsefat
[
44]
1
et al.
Yield 72%. H NMR (300 MHz, CDCl , δ, ppm):
3
1.1 (12H, d), 1.3 (12H, d), 2.3 (12H, s), 2.4 (12H, s), 3.1
+
(4H, sep), 7.1 (4H, d), 7.3 (2H, t). MS (EI, m/z): 618 [M ,
weight (M ) values were calculated according to the
100%]. Anal. Calcd for C42
9.1. Found (%): C, 80.9; H, 9.1; N, 9.5. FT‐IR (KBr, cm ):
275 (―C―N―), 1644 (―C═N―).
H N (%): C, 81.5; H, 9.4; N,
58 4
v
[48,49]
−1
Mark–Houwink equation
:
1
a
η ¼ KMv
(3)
2
.4.3 | Ligand SL2
where the coefficients and
α
K
are 0.69 and
−
2
−1
2
.28 × 10 ml g , respectively. Gel permeation chroma-
The procedure used was that according to Khoshsefat
et al.
ppm): 1.0 (12H, d), 1.3 (12H, d), 2.2 (12H, s), 3.1 (4H,
sep), 6.7 (4H, d), 7.3 (8H, t), 7.9 (4H, t), 8.2 (2H, d).
MS (EI, m/z): 810 [M , 100%]. Anal. Calcd for
[
44]
1
tography (GPC) was conducted with an Agilent 1100
instrument using tetrahydrofuran as eluent, a refractive
index detector at maximum temperature of 45 °C and a
column with a diameter of 0.25 mm. Differential
Yield 67%. H NMR (300 MHz, CDCl , δ,
3
+
SCHEME 1 Synthesis procedure for ligands and catalysts

4
of 9
DECHAL ET AL.
C H N (%): C, 85.89; H, 7.21; N, 6.91. Found (%): C,
3 | RESULTS AND DISCUSSION
58
58 4
−
1
8
5.90; H, 7.09; N, 6.98. FT‐IR (KBr, cm ): 1279
(
―C―N―), 1657 ―C═N―).
To study the catalyst structure, the polymerizations of
‐hexene were carried out using mono‐ and binuclear
1
catalysts at different concentrations of EASC as co‐cata-
lyst (Table 1). As is evident from Table 1, an increase
of the [AlNi] molar ratio leads to high value of conver-
sion and productivity to an optimum value. The cata-
2
.4.4 | Complex MN
The procedure used was that according to Khoshsefat
[44]
−1
et al.
to weak field as it coordinated to the Ni atom; 1625
―C═N―). Anal. Calcd for C H Br N Ni (%): C, 60.12;
FT‐IR (KBr, cm ): the imine signal was shifted
lyst productivity, then, decreased due to the formation
[50]
of inactive species of complexes.
The best [AlNi]
(
36
40
2 2
molar ratios were 1000, 2000 and 1500 for the BN2,
H, 5.61; N, 3.89. Found (%): C, 59.89; H, 5.54; N, 3.91.
BN and MN catalysts, respectively. Moreover, polymer-
1
ization of higher α‐olefins (1‐ocetene and 1‐decene) was
carried out at [AlNi] = 1000. The greater conversion of
1‐octene than 1‐decene is presumably for steric, diffu-
2
.4.5 | Complex BN1
[
51]
sion and solubility reasons.
The procedure used was that according to Khoshsefat
et al.
to weak field as it coordinated to the Ni atom; 1643
[44]
−1
The mechanism proposed for the higher level of
enchainment followed by each insertion facilitated
through the synergistic effect of adjacent second centre
FT‐IR (KBr, cm ): the imine signal was shifted
(
―C═N―). Anal. Calcd for C H Br N Ni (%): C,
42
58
4
4
2
[52]
and optimum bulkiness is depicted in Scheme 2.
4
7,8; H, 5.5; N, 5.3. Found (%): C, 47.1; H, 5.3; N, 5.1.
The represented Ni⋅⋅⋅X interaction suggested for the cat-
alyst/co‐catalyst complex formation is the same as that
explained for methylaluminoxane or borate activation
2
.4.6 | Complex BN2
[53–55]
route.
Binuclear catalysts in most cases have
The procedure used was that according to Khoshsefat
shown the highest catalyst productivities and stabilities
or even higher polymer molecular weights than their
[44]
−1
et al.
FT‐IR (KBr, cm ): the imine signal was shifted
[
28,50,56,57]
to weak field as it coordinated to the Ni atom; 1652
mononuclear analogues.
were observed for the catalysts. For example, in compar-
ison to catalyst BN , catalyst BN showed the highest
Similar behaviours
(
―C═N―). Anal. Calcd for C H Br N Ni (%): C,
58
58
4
4
2
5
5.81; H, 4.68; N, 4.49. Found (%): C, 55.64; H, 4.21; N, 4.06.
1
2
a
TABLE 1 Results of α‐olefin polymerization using BN
1
, BN
2
and MN for various [AlNi] ratios
Productivity
(g mmol cat)
M
v
−1
5
−1
Entry
Catalyst
[AlNi]
Yield (g)
Conv. (%)
(× 10 g mol )
1
2
3
4
5
6
7
8
9
BN
BN
BN
BN
BN
BN
BN
BN
BN
BN
2
2
2
2
2
2
1
1
1
1
600
1000
1500
2000
1000
1000
1000
1500
2000
2500
600
3.12
5.93
2.42
2.09
6.82
6.41
1.38
1.65
2.30
2.22
1.75
2.18
2.05
46.35
88.11
35.95
31.05
94.32
86.15
20.51
24.52
34.17
32.98
26.02
32.39
30.46
1248
2372
968
5.92
8.61
5.26
4.50
10.65
12.78
3.30
2.82
3.15
4.80
3.21
1.15
1.94
836
b
c
2719
2560
552
660
920
1
1
1
1
0
1
2
3
888
MN
MN
700
1500
2000
871
MN
819
a
−3
3
[
catalyst] = 2.5 × 10 mmol; polymerization temperature, 25 °C; polymerization time until gelation; 6 cm of toluene used as solvent.
b
Monomer: 1‐octene.
c
Monomer: 1‐decene.

DECHAL ET AL.
5 of 9
SCHEME 2 Brief proposed mechanism for facilitated insertions and enchainments
productivity and led to a higher molecular weight
poly(1‐hexene). The presence of acenaphthene group
on C―C bond through the increasing of steric hin-
drance caused the reduction of N―Ni―N bond angle
and blocking of axial sites by isopropyl groups. More-
over, the electron‐withdrawing nature of the substituent
and electron deficiency on the metal centre can cause
an increase in the catalyst productivity. On the other
hand, the steric effect on the catalyst backbone leads
to a decrease of the chain transfer reactions and an
increase of the molecular weight of the resulting poly-
for all polymers obtained using bimetallic zirconium cat-
alysts compared to those obtained by monometallic cata-
[
11]
lysts.
It also can be suggested that the polymerization
kinetics of bi‐ and multinuclear catalysts is complex and
different from that of mononuclear catalysts.
Polymerization of 1‐octene and 1‐decene in the pres-
ence of BN2 showed higher molecular weight and
narrower MWD. By increasing the monomer length, as
the insertion and enchainment can be much slower in
comparison to short monomer and also higher electron
density provided by the longer monomer, the chain trans-
fer reaction can be suppressed and thereby molecular
weights increased and MWD decreased.
[44,50,58–62]
mer.
The synergistic effect of the structure
and centres and high local monomer concentration
around the active site of BN2 in comparison to MN
led to higher catalyst productivity. This effect also
caused the higher molecular weight of poly(1‐hexene)
as shown in Scheme 2. The productivity of both MN
Poly(1‐hexene) microstructure (entries 2, 9 and 12
1
13
of Table 1) was investigated using H NMR, C NMR
1
3
and FT‐IR analyses (Figures S19–S27). Moreover,
C
NMR spectra of poly(1‐octene) and poly(1‐decene)
(entries 5 and 6) are included in the supporting infor-
mation (Figures S28 and S29). The chemical shift
values observed for the carbons of poly(1‐hexene) are
and BN catalysts is affected by the backbone structure,
1
while that of BN increased due to the synergistic effect
2
[26,49,50,63–65]
of the two metal centres.
[
10,14,16,45,51]
As evident from Table 2 and shown in Figure 1, the
MWDs of the poly(1‐hexene)s obtained using binuclear
catalysts BN (2.30) and BN (2.46) are slightly broader
in agreement with those of other reports.
The signals observed in the region of 14 ppm are assigned
to the methyl carbons of butyl or longer chain branches.
1
2
than that of the poly(1‐hexene)s obtained using MN
Signals of (ω‐1)CH carbons of the branches appear at
2
14,16]
[
(
1.96). This can be attributed to the electronic effect
22.5–23.2 ppm.
Most of the carbon signals arising
[66]
[45]
around the metal centre of catalyst.
Sampson et al. also
from a long branch appear near 30.00 ppm.
The low‐
reported broader MWDs with multi‐modal distributions
field peaks in the region 33.7–34.7 ppm can be a result of
polymer tacticity, whereas the peak at 33.7 ppm maybe
[
10,16]
a
assigned to isotactic poly(1‐hexene).
The peak
TABLE 2 GPC results of obtained poly(α‐olefin) samples
observed at 37 ppm is related to the CH carbons
5
−1
5
−1
Entry
M
n
(× 10 g mol
)
M
w
(× 10 g mol
)
MWD
[14,16]
associated with the branches in the polymer.
The
2
5
6
9
1.99
4.69
5.49
0.88
0.95
4.9
2.46
1.50
1.39
2.30
1.96
poly(1‐hexene) produced with catalyst BN2 has lower
branching density than that produced with catalyst BN1
7.03
7.65
2.08
1.87
(
Table 3). Similar behaviours were reported by Chen and
[
45]
co‐workers.
This observation may for two reasons: first, the elec-
tronic effect of acenaphthene group on the backbone that
leads to fewer chain transfer reactions; and second, the
1
2
a
Polymerization conditions as Table 1.

6
of 9
DECHAL ET AL.
FIGURE 1 GPC curves of poly(α‐olefin)
s produced using BN
catalysts
1 2
, BN and MN
stronger synergistic effect resulted from chain walk-
monomer length is important in regard to high level of
agostic interaction and distance between the centres.
Moreover, the steric repulsion between the inserted
monomer and the substituents, backbone and bridge
can control the rate‐determining step of propagation,
causing a specific insertion. The higher steric hindrance
[
11,26,45,67,68]
ing.
Also, the poly (1‐hexene) obtained in
the presence of binuclear catalysts showed less chain
branching than that obtained in the presence of mono-
nuclear catalyst (MN). This result can be explained by
the optimum bulkiness and synergistic effect owing to
the presence of a second metal centre and plausible
agostic interaction between the polymer chain and sec-
ond centre, along with the greater chain walking
and stronger synergistic effect of BN is the reason for
2
[18]
the greater extent of 2,1‐insertion (Table 3).
In
addition, re‐enchainment for the binuclear catalysts is
higher than that for the mononuclear analogue, leading
to greater chain walking. This is owing to the electronic
interaction between the metal centres and olefin oligo-
[65,69,70]
(Scheme 2).
The catalysts that have steric hindrance may favour
1
,2‐insertion due to sterically encumbered α‐olefins and
[
24,65]
repulsion with the substituents of the ligand. This trend
is observed for the mononuclear catalyst bearing bulky
substituents in the polymerization of 1‐hexene, while for
the binuclear catalysts, the 2,1‐insertion ratio of mono-
mer is greater. The rotation of N and N–aryl bonds in
the binuclear complexes is possibly due to efficient
agostic interaction which can stabilize the π‐complex
mer/polymer chains.
Chain walking is distinguished with the branching
density, as the polymer chain contains butyl branches
indicating less chain walking, whereas methyl and long‐
chain branches (>C ) suggest greater chain walking.
4
More chain walking for BN in comparison to MN is
2
attributed to the synergistic effect due to optimum bulki-
[18,71–73]
[53,58]
species.
Moreover, polymerization of 1‐octene
ness and presence of a second metal centre.
More-
and 1‐decene using the BN2 catalyst showed the
over, the presence of acenaphthene group in BN and
2
a
TABLE 3 Branching density and distributions of poly(1‐hexene) samples (entries 2, 9 and 12 of Table 1)
Me
(%)
Et
(%)
Pro
(%)
Bu
(%)
Long
(%)
1,2‐ins.
(%)
2,1‐ins.
(%)
2,6‐en.
(%)
1,6‐en.
(%)
T
g
b
c
c
c
c
c
c,d
b
b
b
b
e
Entry
BD
BD
(°C)
2
9
115
117
136
113
116
131
29.7
19.0
26.8
0
2.2
3.2
1.8
59.2
69.5
63.5
8.9
6.6
5.2
67.8
69.6
78.6
32.2
30.4
21.4
39.6
35.0
40.2
44.7
43.5
37.7
−62.1
−63.9
−81.2
1.7
2.7
1
2
a
Polymerization conditions as Table 1.
b
1
Determined by H NMR.
13
c
Determined by C NMR.
d
4
Longer than C .
e
Determined by DSC.

DECHAL ET AL.
7 of 9
the electronic effects lead to greater chain walking for
BN than for BN , causing greater content of methyl
2
1
[
14,18,74]
and long branches (>C ) (Table 3).
4
−
1
The FT‐IR band at 723 cm
representing butyl
branches can confirm the NMR data. The stronger band
−
1
in the region 723–725 cm for BN and MN in compari-
1
son to BN2 shows greater extent of butyl in
[16]
microstructure.
The broad melting points obtained when using the
binuclear catalysts can be observed in the DSC thermo-
grams of the samples shown in Figure S30 (supporting
information). These thermal properties can be attributed
to the sequence of melting points followed by recrystalli-
zation steps of less ordered domains with the variable
[
18,75,76]
degrees of chain straightening and branching.
The higher glass transition temperature of the poly(1‐
hexene) obtained using catalyst BN also confirmed this
2
[
77]
claim in relation to chain mobility.
Greater diversity
and density in branching could lead to high chain mobil-
ity. For higher α‐olefins, higher linearity led to higher
glass transition, melting area and melting point
(Table 4). As a result, the affinity of binuclear catalysts
for 1,2‐insertion was increased by longer monomer
length.
For the BN catalyst, the effects of polymerization
2
parameters were investigated at the optimum [AlNi]
molar ratio. Polymerization of 1‐hexene using BN in
2
the presence of EASC showed that EASC is an efficient
activator leading to high catalyst productivity. The results
are probably due to high alkylating and acid strength,
[41,64]
FIGURE 2 1‐Hexene polymerization with BN2 catalyst under
various conditions: (a) polymerization temperature; (b)
polymerization time. Polymerization conditions:
causing more activation of metal centres.
Further-
more, the polymerization temperature can affect the
activity of the catalyst. To clarify, a higher polymerization
temperature improved the catalyst performance up to
−
3
3
[catalyst] = 2.5 × 10 mmol, Al/Ni = 1000, 6 cm of toluene as
solvent with a time of 12 h (a) and at 25 °C (b)
2
5 °C (room temperature) (Figure 2a) through increasing
the kinetic energy of 1‐hexene, which facilitates the trans-
fer of the monomer to the catalytic active centres and
increases the alkylation reaction of metal centres. Irre-
versible deactivation of the active centres and reduction
of monomer solubility at higher polymerization tempera-
ture lead to a reduction of the catalyst productivity.
For the MN catalyst, a same trend was observed; how-
ever, at 60 °C the mononuclear catalyst was almost
inactive. This can be attributed to the high thermal stabil-
ity of the binuclear catalyst.
The highest polymerization productivity was obtained
after 12 h of reaction (Figure 2b), the conversion increas-
ing with time. Degradation and deactivation of active
centres and increasing viscosity of polymerization media
inhibited the insertion of monomer and decreased the
[
71,78]
[
79]
catalyst productivity.
a
TABLE 4 Microstructural and thermal properties of poly(1‐octene) and poly(1‐decene) samples
BD
(per 1000 C)
Me
(%)
Et
(%)
Pr
(%)
Bu
(%)
≥C
(%)
6
1,2‐
(%)
2,1‐
(%)
1,ω
(%)
T
(°C)
g
ΔH
(J g
T
m
b
c
−1 c
c
Entry
)
(°C)
5
6
88.2
80.3
23.5
13.4
0
0
0.3
0.1
0
0
76.2
86.5
70.5
80.3
29.5
19.7
40.0
30.8
−59.6
−58.3
23.5
31.7
12.7
24.1
a
Polymerization condition as Table 1.
b
13
Determined by C NMR.
c
Determined by DSC.

8
of 9
DECHAL ET AL.
[
7] I. Kim, J. M. Zhou, H. Chung, J. Polym, Sci. A: Polym. Chem.
4
| CONCLUSIONS
2000, 38, 1687.
A mononuclear and two new binuclear α‐diimine Ni‐
based catalysts were prepared, characterized and used in
polymerization of 1‐hexene. Catalyst BN2 showed the
highest catalyst productivity which resulted in higher
molecular weight and broader MWD of polymers in com-
[8] S. M. M. Mortazavi, Iranian Polym. J. 2016, 25, 731.
[
9] P. D. Pletcher, J. M. Switzer, D. K. Steelman, G. A. Medvedev,
W. N. Delgass, J. M. Caruthers, M. M. Abu‐Omar, ACS Catal.
2016, 6, 5138.
[10] F. Nouri‐Ahangarani, N. Bahri‐Laleh, M. Nekoomanesh‐
Haghighi, M. Karbalaie, Monomers Polym. 2016, 19, 394.
parison to BN and MN catalysts. The synergistic effect
1
between the centres due to high local concentration of
monomer at active‐centre environment, efficient steric
hindrance and electronic effects through optimum bulki-
ness are the reasons of these observations. These are also
the reasons suggested for the pronounced chain walking
[
11] J. Sampson, G. Choi, M. N. Akhtar, E. A. Jaseer, R.
Theravalappil, H. A. Al‐Muallem, T. Agapie, Organometallics
2017, 36, 1915.
[12] P. L. Santos, M. Castier, Polymer 2007, 48, 5152.
[
[
[
13] G. Leone, M. Mauri, F. Bertini, M. Canetti, D. Piovani, G. Ricci,
of catalyst BN due to higher methyl branch contents.
2
Macromolecules 2015, 48, 1304.
The glass transition temperatures of the samples in
relation to the microstructures were in the range −58 to
14] U. Subramanyam, P. R. Rajamohanan, S. Sivaram, Polymer
2
004, 45, 4063.
15] N. Nakata, Y. Saito, T. Watanabe, A. Ishii, Top. Catal. 2014, 57,
18.
−
81 °C, and broadening the melting peaks showed that
chain walking led to chain straightening and methyl
branching, which, in turn, decreased the chain mobility.
Polymerization of longer α‐olefins led to higher produc-
tivity and conversion. This result was along with higher
molecular weight and narrow MWD. Lower branching
densities and higher melting point and broader melting
area were the further observations. Moreover, polymeri-
zation at higher temperature revealed the thermal
stability of binuclear catalysts in comparison to the
mononuclear analogue. Longer polymerization times,
however, caused a higher catalyst productivity and Mv.
9
[16] S. Ahmadjo, Polym. Adv. Technol. 2016, 27, 1523.
[17] H. Hu, H. Gao, D. Chen, G. Li, Y. Tan, G. Liang, Q. Wu, ACS
Catal. 2014, 5, 122.
[
[
[
18] S. Takano, D. Takeuchi, K. Osakada, Chem. – Eur. J. 2015, 21,
16209.
19] Y. Na, X. Wang, K. Lian, Y. Zhu, W. Li, Y. Luo, C. Chen,
ChemCatChem 2017, 9, 1062.
20] S. Liu, A. Motta, M. Delferro, T. J. Marks, J. Am. Chem. Soc.
2013, 135, 8830.
[
[
[
21] H. Mu, L. Pan, D. Song, Y. Li, Chem. Rev. 2015, 115, 12091.
22] H. K. Luo, H. Schumann, J. Mol. Catal. A 2005, 227, 153.
ACKNOWLEDGEMENT
23] M. R. Radlauer, A. K. Buckley, L. M. Henling, T. Agapie, J. Am.
Chem. Soc. 2013, 135, 3784.
The authors are grateful to the Iran Polymer and Petro-
chemical Institute (IPPI).
[24] A. Motta, I. L. Fragalà, T. J. Marks, J. Am. Chem. Soc. 2009, 131,
974.
3
[
25] M. P. Weberski, C. Chen, M. Delferro, T. J. Marks, Chem. – Eur.
ORCID
J. 2012, 18, 10715.
Saeid Ahmadjo http://orcid.org/0000-0002-8536-115X
[26] J. P. McInnis, M. Delferro, T. J. Marks, Acc. Chem. Res. 2014,
47, 2545.
Gholam Hossein Zohuri
363
http://orcid.org/0000-0003-2380-
8
[27] Z. Chen, E. Yao, J. Wang, X. Gong, Y. Ma, Macromolecules
2016, 49, 8848.
[
28] Q. Xing, T. Zhao, S. Du, W. Yang, T. Liang, C. Redshaw, W. H.
REFERENCES
Sun, Organometallics 2014, 33, 1382.
[
[
[
1] K. Lian, Y. Zhu, W. Li, S. Dai, C. Chen, Macromolecules 2017,
[
29] J. Liu, Y. Li, J. Liu, Z. Li, Macromolecules 2005, 38, 2559.
30] B. A. Rodriguez, M. Delferro, T. J. Marks, J. Am. Chem. Soc.
5
0, 6074.
[
2] Y. Chen, L. Wang, H. Yu, Y. Zhao, R. Sun, G. Jing, J. Huang, H.
Khalid, N. M. Abbasi, M. Akram, Prog. Polym. Sci. 2015, 45, 23.
2009, 131, 5902.
[31] R. Wang, X. Sui, W. Pang, C. Chen, ChemCatChem 2016, 8,
3] R. Gao, W. H. Sun, C. Redshaw, Catal. Sci. Technol. 2013, 3,
434.
1
172.
[32] L. Guo, H. Gao, Q. Guan, H. Hu, J. Deng, J. Liu, Q. Wu, Organ-
ometallics 2012, 31, 6054.
[
[
[
4] C. Guo, L. Zhou, J. Lv, Polym. Compos. 2013, 21, 449.
[
[
33] L. Guo, S. Dai, X. Sui, C. Chen, ACS Catal. 2016, 6, 428.
34] L. Guo, W. Liu, C. Chen, Mater. Chem. Front. 2017, 1, 2487.
5] M. Zhao, C. Chen, ACS Catal. 2017, 7(11), 7490.
6] A. I. Kramer, P. Surana, P. J. Nandapurkar, N. Yang, US Patent
7
547811, 2009.
[35] G. G. Hlatky, Chem. Rev. 2000, 100, 1347.

DECHAL ET AL.
9 of 9
[
[
36] N. V. Kulkarni, T. Elkin, B. Tumaniskii, M. Botoshansky, L. J.
[62] C. S. Popeney, Z. Guan, Macromolecules 2010, 43, 4091.
Shimon, M. S. Eisen, Organometallics 2014, 33, 3119.
[63] B. K. Bahuleyan, U. K. Lee, C. S. Ha, I. Kim, Appl. Catal. A
2008, 351, 36.
37] D. J. Tempel, L. K. Johnson, R. L. Huff, P. S. White, M.
Brookhart, J. Am. Chem. Soc. 2000, 122, 6686.
[64] S. Kong, K. Song, T. Liang, C. Y. Guo, W. H. Sun, C. Redshaw,
[
[
[
38] L. Guo, C. Chen, China Chem. 2015, 58, 1663.
Dalton Trans. 2013, 42, 9176.
39] D. Zhang, C. Chen, Angew. Chem. Int. Ed. 2017, 56, 14672.
40] M. Li, X. Wang, Y. Luo, C. Chen, Angew. Chem. Int. Ed. 2017,
[65] H. Li, T. J. Marks, Proc. Natl Acad. Sci. USA 2006, 103, 15295.
[66] Y. B. Huang, G. R. Tang, G. Y. Jin, G. X. Jin, Organometallics
2008, 27, 259.
5
6, 11604.
[
[
41] M. Chen, C. Chen, ACS Catal. 2017, 7, 1308.
[67] F. S. Liu, H. B. Hu, Y. Xu, L. H. Guo, S. B. Zai, K. M. Song, Q.
Wu, Macromolecules 2009, 42, 7789.
42] G. Song, W. Pang, W. Li, M. Chen, C. Chen, Polym. Chem.
2
017, 8, 7400.
[68] D. Meinhard, M. Wegner, G. Kipiani, A. Hearley, P. Reuter, S.
Fischer, B. Rieger, J. Am. Chem. Soc. 2007, 129, 9182.
[
[
43] B. Yang, S. Xiong, C. Chen, Polym. Chem. 2017, 8, 6272.
[
69] R. Wang, X. Sui, W. Pang, C. Chen, ChemCatChem 2016, 8,
44] M. Khoshsefat, G. H. Zohuri, N. Ramezanian, S. Ahmadjo, M.
434.
Haghpanah, J. Polym. Sci., Part A: Polym. Chem. 2016, 54,
3
000.
45] J. D. Azoulay, G. C. Bazan, G. B. Galland, Macromolecules
010, 43, 2794.
46] J. Merna, Z. Hošt'álek, J. Peleška, J. Roda, Polymer 2009, 50,
016.
[70] Y. Gao, A. R. Mouat, A. Motta, A. Macchioni, C. Zuccaccia, M.
Delferro, T. J. Marks, ACS Catal. 2015, 5, 5272.
[
[
[
2
[71] D. H. Camacho, Z. Guan, Macromolecules 2005, 38, 2544.
[72] H. Li, T. J. Marks, Proc. Natl Acad. Sci. USA 2006, 103, 15295.
5
[73] A. Motta, I. L. Fragala, T. J. Marks, J. Am. Chem. Soc. 2009, 131,
47] E. F. McCord, S. J. McLain, L. T. Nelson, S. D. Ittel, D. Tempel,
3974.
C. M. Killian, M. Brookhart, Macromolecules 2007, 40, 410.
[74] G. Leone, M. Mauri, I. Pierro, G. Ricci, M. Canetti, F. Bertini,
[
48] M. Hoff, W. Kaminsky, Macromol. Chem. Phys. 2004, 205, 1167.
49] F. C. Lin, S. S. Stivala, J. A. Biesenberger, J. Appl. Polym. Sci.
Polymer 2016, 100, 37.
[
[75] F. AlObaidi, Z. Ye, S. Zhu, Polymer 2004, 45, 6823.
1
973, 17, 1073.
[76] F. Liu, H. Gao, Z. Hu, H. Hu, F. Zhu, Q. Wu, J. Polym. Sci., Part
[
50] L. Wang, J. Sun, Theor. Chim. Acta 2008, 361, 1843.
A: Polym. Chem. 2012, 50, 3859.
[
51] I. Pierro, G. Zanchin, E. Parisini, J. Martí‐Rujas, M. Canetti, G.
Ricci, F. Bertini, G. Leone, Macromolecules 2018, 51, 801.
[77] R. Pethrick, Polymer Science and Technology, CRC Press, New
York 2010.
[
[
[
52] I. Kim, C. H. Kwak, J. S. Kim, C. S. Ha, Appl. Catal. A 2005,
[78] H. Jiang, F. He, J. Lu, Y. Xing, J. Mol. Catal. A 2013, 380, 139.
2
87, 98.
53] R. F. de Souza, L. C. Simon, M. A. Maria do Carmo, J. Catal.
003, 214, 165.
[79] J. L. Rhinehart, L. A. Brown, B. K. Long, J. Am. Chem. Soc.
2013, 135, 16316.
2
54] S. Damavandi, N. Samadieh, S. Ahmadjo, Z. Etemadinia, Eur.
Polym. J. 2015, 64, 118.
SUPPORTING INFORMATION
Additional Supporting Information may be found online
in the supporting information tab for this article.
[
55] M. Delferro, T. J. Marks, Chem. Rev. 2011, 111, 2450.
[
56] G. Tian, B. Wang, S. Xu, X. Zhou, B. Liang, L. Zhao, Y. Li,
Macromol. Chem. Phys. 2002, 203, 31.
[
[
57] Q. Chen, J. Yu, J. Huang, Organometallics 2007, 26, 617.
How to cite this article: Dechal A, Khoshsefat
M, Ahmadjo S, Mortazavi SMM, Zohuri GH,
Abedini H. Mono‐ and binuclear nickel catalysts
for 1‐hexene polymerization. Appl Organometal
Chem. 2018;e4355. https://doi.org/10.1002/aoc.4355
58] L. Zhu, Z. S. Fu, H. J. Pan, W. Feng, C. Chen, Z. Q. Fan, Dalton
Trans. 2014, 43, 2900.
[59] F. AlObaidi, Z. Ye, S. Zhu, Polymer 2004, 45, 6823.
[60] D. H. Camacho, Z. Guan, Chem. Commun. 2010, 46, 7879.
[61] L. Guo, S. Dai, C. Chen, Polymer 2016, 8, 37.