Novel late transition metal catalysts based on iron: Synthesis, structures and ethylene polymerization

Article abstract of DOI:10.1007/s10562-010-0433-x

In this article we reported synthesis, characterization and ethylene polymerization behavior of two new late transition metal 2,6-bis(imino)pyridine catalysts based on iron(II) possessing different substituents of NO₂ (catalyst b) and OMe (catalyst c) at the para position of the pyridine ring. Theoretical study exhibited more positive charge on the central metal of the catalyst b, leading to higher activity offset by lower thermal stability and life time.

Full text of DOI:10.1007/s10562-010-0433-x

Catal Lett (2010) 140:160–166
DOI 10.1007/s10562-010-0433-x
Novel Late Transition Metal Catalysts Based on Iron: Synthesis,
Structures and Ethylene Polymerization
•
Gholam Hossein Zohuri Seyed Mohammad Seyedi
•
•
Reza Sandaroos Saman Damavandi
•
Ali Mohammadi
Received: 22 July 2010 / Accepted: 11 August 2010 / Published online: 8 September 2010
Ó Springer Science+Business Media, LLC 2010
Abstract In this article we reported synthesis, charac-
terization and ethylene polymerization behavior of two
new late transition metal 2,6-bis(imino)pyridine catalysts
based on iron(II) possessing different substituents of NO2
(catalyst b) and OMe (catalyst c) at the para position of the
pyridine ring. Theoretical study exhibited more positive
charge on the central metal of the catalyst b, leading to
higher activity offset by lower thermal stability and life
time.
accelerated b-hydride elimination [3]. However, in 1995
Brookhart and coworkers succeeded in polymerizing eth-
ylene to high polymers by using Ni(II) and Pd(II) catalysts.
These catalysts are unique in polymerization of ethylene to
give a variety of materials, ranging from highly viscous
liquids to rubbery elastomeric materials, to rigid linear
polyethylenes [4]. The activity of these catalysts could
reach up to 1.1 9 105 (gr PE/(mmol catalyst 9 h)) [5].
In 1998, Brookhart, Bennett and Gibson independently
discovered that five-coordinate 2,6-bis(imino)pyridine
(BIMP) Fe(II) and Co(II) dihalides, activated by MAO, are
effective catalysts for the conversion of ethylene either to
high-density polyethylene or to a-olefins. Remarkably, the
productivities were as high as those of most efficient
metallocenes [6–10]. The advantages of BIMP catalysts
over other types of single-site Ziegler–Natta and metallo-
cene catalysts for ethylene homopolymerization are mani-
fold, spanning from the ease of preparation and handling to
the use of low-cost metals with negligible environmental
impact.
Keywords Polyethylene ꢀ Fe-based catalyst ꢀ BIMP–Fe
catalyst ꢀ Late transition metal catalyst ꢀ Slurry
polymerization
1 Introduction
The polymerization of ethylene was discovered in 1933,
but the first generation of effective transition metal poly-
merization catalysts was developed only 20 years later by
Ziegler and Natta [1, 2]. After discovering of Ziegler–Natta
catalysts, ethylene polymerization and oligomerization
processes catalyzed by transition metal have become a
great importance in both academic and industrial fields. In
the past, late transition metal catalysts were generally
accepted that they produced oligomers because of the
An intriguing feature of BIMP catalysts is provided by
the facile tuning of their polymerization activity by simple
modifications of the ligand architecture. It has been shown,
in fact, that the size, nature and regiochemistry of the
substituents in the iminoaryl groups has crucial importance
in controlling the polymerization and oligomerization
[11–14]. One of the aims we have in mind is to study the
correlation between the catalyst structure and catalyst
activity as well as thermal stability and catalyst lifetime
during the polymerization. For these reason, our research
group was interested in investigating the effects of sub-
stituents at the pyridine ring on behavior of the BIMP
catalysts. In this work, we report the synthesis and char-
acterization of two new BIMP catalysts, catalysts b and c,
in which there are different substituents with various
G. H. Zohuri (&) ꢀ S. M. Seyedi ꢀ R. Sandaroos (&) ꢀ
S. Damavandi ꢀ A. Mohammadi
Department of Chemistry, Faculty of Science,
Ferdowsi University of Mashhad, P.O. Box 91775,
Mashhad, Iran
e-mail: G.Zohuri@ippi.ac.ir
R. Sandaroos
e-mail: R_Sandaroos@yahoo.com
123

Novel Late Transition Metal Catalysts Based on Iron
161
electronic properties at the para position of the pyridine
ring (Fig. 1). To elucidate the merit of our research, we
made a comparison between the results of polymerization
behavior and catalyst activities of the prepared catalysts
and a well-known late transition metal catalyst of a. The
replacement of para substituents from H to OMe and NO2
is not expected to obtain significant change in steric bulk.
For these complexes it is presumable that the elec-
tronic effect is more important than the steric effect.
Furthermore, some specification of the resulted polymer
was studied.
refluxed over an appropriate drying agent and distilled and
degassed prior to use.
The viscosity average molecular weight (Mv) of some
polymer samples were determined according to the litera-
ture [15, 16]. Intrinsic viscosity [g] was measured in
decaline at 135 °C using an Ubbelohde viscometer. Mv
values were calculated through equation [g] = 6.2 9 10-4
M0v.7 [25]. Differential scanning calorimetry (DSC) (Uni-
versal V4IDTA) with a rate of 10 °C/min instrument was
used for polymer characterization. The degree of crystal-
linity of a polyethylene sample can be calculated from its
heat of fusion which can be determined by differential
scanning calorimetry. Comparison of the measured heat of
fusion with that estimated for 100% crystalline polyethyl-
ene yields the fraction of the sample in the crystal lattice. In
practice, the heat of fusion of pure crystalline polyethylene
is taken to be in the range of 66–70 cal/g, with a commonly
accepted value being 69 cal/g [26]. According to the lit-
erature [17], calculation of DHf/DHf* 9 100 gives the
values of crystallinity where DHf is the heat of fusion and
2 Experimental
2.1 General
All manipulations were carried out under an atmosphere of
nitrogen using standard Schlenk and cannula techniques or
in a conventional nitrogen-filled glovebox. Solvents were
NO2
Y
(i)
(ii)
(iv)
N
O
N
N
O
N
OMe
(iii)
(iv)
(5): Y = NO2
(6): Y = OMe
(3)
(2)
(1)
N
O
(4)
Y
N
Y
Y
N
Y
N
N
N
(v)
(vii)
(vi)
HO
OH
N
O
O
O
O
(10): Y = H
(11): Y = NO2
(12): Y = OMe
(a'): Y = H
(b'): Y = NO2
(c'): Y = OMe
(5): Y = NO2
(6): Y = OMe
Y = H
(7): Y = H
(8): Y = NO2
(9): Y = OMe
Y
(viii)
N
12-14
N
N
Fe
Cl
Cl
(a): Y = H
(b): Y = NO2
(c): Y = OMe
(i) H2O2; (ii) HNO3 / H2SO4; (iii) MeOH / MeO; (iv) PPh3; (v) KMnO4; (vi) SOCl2, NH(CH2CH2OMe)2 /
NEt3, MeLi, H2O; (vii) HCO2H, 2,4,6-trimethylaniline; (viii) FeCl2
Fig. 1 Synthetic procedure of ligands a0–c0 and catalysts a–c
123

162
G. H. Zohuri et al.
DHf* = 69 cal/g is the heat of fusion of 100% crystalline
polyethylene.
7.71 (s, 2H), 2.55 (s, 6H). Anal. (C7H8N2O3) calcd: C, 50.00;
H, 4.80; N, 16.66. Found: C, 49.39; H, 4.76; N, 16.59.
Elemental analysis for CHN was carried out by the
1
CHNO type from the Helaus Co. H NMR spectra were
2.4 4-Methoxy-2,6-lutidine-1-oxide (4)
recorded on a Bruker spectrometer (500 MHz) at 293 K.
2,6-Lutidine, MAO (10%), 2,4,6-trimethylaniline and
other chemicals were purchased from Sigma-Aldrich
Chemical Co.
22.8 g (0.13 mol) of 4-Nitro-2,6-lutidine-1-oxide (3) and
250 mL of absolute methanol, was added a cooled solution
of sodium methoxide prepared by the addition of 3.45 g
of fresh sodium to 200 mL of absolute methanol. The
resulting mixture was heated under reflux on a steam-bath
with continuous stirring for 5 h. The reaction mixture was
distilled to dryness with continuous stirring and the residue
dissolved in 100 mL of cold water. Concentrated hydro-
chloric acid was added to constant pH 4 to decompose
sodium nitrite formed during the reaction. The resulting
mixture was chilled at 5 °C for 6–8 h and the product fil-
tered by suction, washed with ice-water, and dried at
100 °C to give 15.2 (76.6%) of solide. The crude product
was recrystallized from boiling water/ethanol to give
The general procedure of polymerization was to dissolve
of precatalyst in toluene (300 mL) and adding of MAO
(10 wt% in toluene) to produce an orange solution. The
reactor was purged with ethylene, and the contents were
stirred and maintained under ethylene for the duration of
the polymerization. The polymerization was terminated by
the addition of aqueous hydrogen chloride. The solid PE
was collected by filtration, washed with methanol (50 mL),
and dried (vacuum oven at 50 °C).
2.2 2,6-Lutidine-1-oxide (2)
1
4-methoxy-2,6-lutidine-1-oxide (4). H NMR (CDCl3); d,
8.41 (s, 2H), 2.35 (s, 6H). Anal. (C8H11NO2) calcd: C,
To a mixture of 30–35 mL of glacial acetic acid and 10.8 g
(0.1 mol) of 2,6-lutidine was added, with shaking, 16 mL
(0.14 mol) of cold (5 °C) 30% hydrogen peroxide. The
mixture was heated for 27 h at 70 °C. The reaction mixture
was concentrated as much as possible in a vacuum and
treated with portions of hot saturated aqueous sodium
carbonate solution until an alkaline test was obtained. The
mixture was extracted with chloroform and the extracts
were concentrated at 80 °C. The precipitated inorganic
salts were removed by hot filtration and the filtrate again
concentrated to the smallest possible volume. On standing,
the residue crystallized, and the following day it was bro-
ken up under ether, filtered and washed with ether. The
crystalline 2,6-lutidine-1-oxide so obtained weighed 9.6 g
(78%) [18]. 1H NMR (CDCl3); d, 7.13 (t, 1H), 7.05 (d, 2H),
2.50 (s, 6H). Anal. (C7H9NO) calcd: C, 68.27; H, 7.37; N,
11.37. Found: C, 67.20; H, 7.31; N, 11.33.
62.73; H, 7.24; N, 9.14. Found: C, 61.98; H, 7.20; N, 9.10.
2.5 4-Nitro-2,6-lutidine (5)
A mixture of 16.8 g. (0.1 mol) of 2,6-lutidine-4-nitro-1-
oxide (3) and 26.6 g. (0.1 mol) of triphenylphosphine in
triethylene glycol (100 mL) was heated to 200 °C for 1 h
and then cooled to room temperature. The mixture was
filtered, the filtrate was dried under reduced pressure and
the obtained crude product recrystallized from petroleum
ether. The yield of 2,6-dimethyl-4-nitro pyridine was
9.27 g (61%) [19]. 1H NMR (CDCl3); d, 8.21 (s, 2H), 3.74
(s, 3H), 2.36 (s, 6H). Anal. (C7H8N2O2) calcd: C, 55.26; H,
5.30; N, 18.41. Found: C, 55.01; H, 5.27; N, 18.11.
2.6 4-Methoxy-2,6-Lutidine (6)
2.3 4-Nitro-2,6-lutidine-1-oxide (3)
By using the procedure described in (3.5) above, 4 was
1
10 g of 2,6-lutidine-1-oxide (0.08 mol) was dissolved in a
mixture of 30 mL of sulfuric acid (sp. gr. 1.84) and 12 g of
nitric acid (sp. gr. 1.48), and the solution was heated 7 h at
128–130 °C. The reaction mixture was poured onto ice and,
with stirring, neutralized with portions of sodium carbonate.
Just when crystals of sodium sulfate began to precipitate, the
neutralization was interrupted and the precipitated crystals
were collected, washed with ice-water, and dried. The filtrate
was extracted with chloroform and the extracts concentrated,
whereupon the residue crystallized. The crystals were
recrystallized from acetone. The yield of 4-nitro-2,6-luti-
converted to 6 in 67% yield. H NMR (CDCl3); d, 6.67
(s, 2H), 3.70 (s, 3H), 2.29 (s, 6H). Anal. (C8H11NO) calcd:
C, 70.04; H, 8.08; N, 10.21. Found: C, 69.63; H, 8.01; N,
10.14.
2.7 Pyridine-2,6-dicarboxylic acid (7)
The compound 7 was synthesized according to the literature
1
[20] in 70% yield (17.24 g). H NMR (CDCl3); d, 8.72 (s,
2H), 8.26 (d, 2H), 8.11 (t, 1H). Anal. (C7H5NO4) calcd: C,
1
50.31; H, 3.02; N, 8.38. Found: C, 49.88; H, 3.00; N, 8.31.
dine-1-oxide was 8.7 g (65%) [18]. H NMR (CDCl3); d,
123

Novel Late Transition Metal Catalysts Based on Iron
2.8 4-Nitro-pyridine-2,6-dicarboxylic acid (8)
163
calcd: C, 73.28; H, 6.83; N, 12.66. Found: C, 73.18; H,
6.81; N, 12.56.
By using the same procedure described in (2.7) above, 5
was converted to 8 in 48% yield. 1H NMR (CDCl3); d, 8.81
(s, 2H), 8.55 (s, 2H). Anal. (C7H4N2O6) calcd: C, 39.64; H,
1.90; N, 13.21. Found: C, 39.011; H, 1.88; N, 13.18.
2.15 4-Methoxy-2,6-diacethyl pyridine bis(2,4,6-
trimethylphenylimine) (c0)
By using the same procedure described in (2.13) above, 15
1
was obtained in 73% yield as an orange solid. H NMR
2.9 4-Methoxy-pyridine-2,6-dicarboxylic acid (9)
(CDCl3): d, 7.31 (s, 2H), 6.94 (s, 4H), 2.31 (s, 6H), 2.27
(s, 6H), 2.05 (s, 12H). Anal. (C28H33N3O) calcd: C, 78.65;
H, 7.78; N, 9.83. Found: C, 78.50; H, 7.71; N, 9.79.
By using the same procedure described in (2.7) above, 6
was converted to 9 in 61% yield. 1H NMR (CDCl3); d, 8.74
(s, 2H), 7.75 (s, 2H), 3.68 (s, 3H). Anal. (C8H7NO5) calcd:
C, 48.74; H, 3.58; N, 7.10. Found: C, 48.22; H, 3.51; N,
7.04.
2.16 (2,6-Diacetylpyridinebis(2,4,6-trimethylanil))
FeCl2 (a)
2.10 2,6-Diacethylpyridine (10)
The complex a was prepared according to the literature
1
[22] in 75% yield as a dark blue solid. H NMR (CD2Cl2,
The compound 7 was converted to the compound 10
1
according to the literature [21] in 71% yield. H NMR
broad singlets are observed in each case): d, 83.70 (2H,),
40.11 (1H,), 21.82 (6H), 15.75 (4H), 13.01 (12H), -21.32
(6H). Anal. (C27H31Cl2FeN3) calcd: C, 61.85; H, 5.96; N,
8.01. Found: C, 61.81; H, 5.92; N, 7.96.
(CDCl3); d, 8.16 (d, 2H), 7.98 (t, 1H), 2.57 (s, 6H). Anal.
(C9H9NO2) calcd: C, 66.25; H, 5.56; N, 8.58. Found: C,
65.88; H, 5.51; N, 8.49.
2.17 (4-Nitro-2,6-diacetylpyridinebis(2,4,6-trimeth-
ylanil))FeCl2 (b)
2.11 4-Nitro-2,6-diacethylpyridine (11)
By using the sam procedure described in (2.10) above, 8
1
By using the same procedure described in (2.16) above,
1
complex b was obtained in 73% yield as a blue solid. H
was converted to 11 in 76% yield. H NMR (CDCl3); d,
8.69 (s, 2H), 2.54 (s, 6H). Anal. (C9H9NO2) calcd: C,
NMR (CD2Cl2, broad singlets are observed in each case):
d, 82.12 (2H,), 21.80 (6H), 15.62 (4H), 13.03 (12H),
-21.11 (6H). Anal. (C27H30Cl2FeN4O2) calcd: C, 56.96;
H, 5.31; N, 9.84. Found: C, 56.91; H, 5.29; N, 9.80.
66.25; H, 5.56; N, 8.58. Found: C, 65.99; H, 5.50; N, 8.52.
2.12 4-Methoxy-2,6-diacethylpyridine (12)
By using the procedure described in (2.10) above, 9 was
1
converted to 12 in 79% yield. H NMR (CDCl3); d, 7.69
(s, 2H), 3.72 (s, 3H), 2.51 (s, 6H). Anal. (C10H11NO3) calcd:
2.18 (4-Methoxy-2,6-diacetylpyridinebis(2,4,6-trim-
ethylanil))FeCl2 (c)
C, 62.17; H, 5.74; N, 7.25. Found: C, 61.95; H, 5.71; N, 7.19.
By using the same procedure described in (2.16) above,
1
complex c was obtained in 69% yield as a blue solid. H
2.13 2,6-Diacethyl pyridine bis(2,4,6-trimethylphenyli-
mine) (a0)
NMR (CD2Cl2, broad singlets are observed in each case):
d, 82.31 (2H,), 21.72 (6H), 15.55 (4H), 13.10 (12H),
-21.21 (6H). Anal. (C28H33Cl2FeN3O) calcd: C, 60.67; H,
6.00; N, 7.58. Found: C, 60.61; H, 5.91; N, 7.51.
The compound a0 was synthesized according to the literature
1
[22] in 80% yield as a yellow solid. H NMR (CDCl3): d,
8.50 (d, 2H), 7.95 (t, 1H), 6.94 (s, 4H), 2.33 (s, 6H), 2.28
(s, 6H), 2.05 (s, 12H). Anal. (C27H31N3) calcd: C, 81.57; H,
7.86; N, 10.57. Found: C, 81.39; H, 7.80; N, 10.53.
3 Results and Discussion
2.14 4-Nitro-2,6-diacethyl pyridine bis(2,4,6-
trimethylphenylimine) (b0)
After investigating the oligomerization of ethylene over
a-diiminenickel(II) catalysts, Brookhart pointed out that, in
addition to ethylene pressure, reaction temperature, reac-
tion time and cocatalyst, oligomerization reaction is
affected by the electronic effects of the catalyst [23].
Lowering of the electron density on the metal center
through the addition of ligands with electron-withdrawing
By using the same procedure described in (2.13) above, the
compound b0 was obtained in 82% yield as a pale yellow
solid. 1H NMR (CDCl3): d, 8.79 (s, 2H), 6.92 (s, 4H), 2.35
(s, 6H), 2.25 (s, 6H), 2.01 (s, 12H). Anal. (C27H30N4O2)
123

164
G. H. Zohuri et al.
groups produces more active catalysts. As we know, Ni has
3d8 and Zr 4d2 electrons. Therefore, late transition metals
are electron-rich compared to early transition metals. This
difference in intrinsic character will be responsible for
catalytic performance. In previous studies, MM based
calculations together with the QEq method were employed
to consider the catalytic performance of metallocene cat-
alysts for the polymerization or copolymerization of olefins
[24, 25]. Activities of the catalysts were successfully cor-
related with the net charges on the central metal. These
results follow Olive’s concept, in that the stronger the
electron-donating ability of the ligand connected with the
central metal atom, the lower is the net charge on the metal,
and the higher the activity of the polymerization [26].
In order to evaluate the electronic effects of para sub-
stituents on the pyridine ring on the activity of BIMP–Fe
catalysts in the polymerization of ethylene, we synthesized
three BIMP–Fe catalysts with different substituents on the
para position of pyridine (Fig. 1).
Fig. 2 Effect of temperature on the average rate of polymerization.
Polymerization conditions: Polymerization time = 60 min, monomer
Pressure = 5 bar, [Al]:[Fe] = 1000:1, [Fe] = 0.3 9 10-3 mmol, tol-
uene = 300 mL, stirrer speed = 800 rmp
slowly for the highest temperatures. But for the catalyst b,
the activity reaches to its maximum around 15 °C and then
dramatically decreases with increasing of the temperature.
For the catalyst c, the activity gradually increases for the
lowest temperatures and reaches a maximum around 60 °C
and after that nearly remains constant. An increase in the
values of the propagation rate constant with increasing the
temperature and irreversible deactivation of the active sites
at high temperature were reported [28]. Additionally,
higher temperature facilitates transfer of the monomer to
the catalytic active centers, meanwhile solubility of the
monomer gas in the polymerization solvent decreased with
increasing temperature [17, 29].
We employed the Gaussian software [27] to calculate
the most probable conformations And QEq charges of
catalysts a–c. A comparison between the activity and QEq
Charge is shown in Table 1. The electron-withdrawing
abilities of the para substituents on the pyridine were varied
by introducing nitro, hydrogen and methoxy gropus for
catalysts a–c, respectively. According to Table 1, the
sequence of QEq charges matches well with those of the
electron-withdrawing abilities. For example, the nitro
group is electron-poorer than the other moieties, leading to
a more electrophilic metal center, i.e. a higher charge value
(0.4844) for Fe. The relationship between activity and net
charge of the central metal atom thus is: the higher the
charge, the higher the activity, which is different from
those for early transition metal systems.
These observations indicate that the activities of the
catalysts a and b are more sensitive to variation of tem-
perature than the catalyst c.
The influence of the polymerization temperature on the
catalytic activity has also been investigated. The poly-
merization was carried out at temperatures between 0 and
75 °C (Fig. 2). For the catalyst a, the catalytic activity
increases for the lowest polymerization temperatures,
reaches a maximum around 40 °C and then decreases
Figure 3 shows the activities versus reaction time for the
three catalysts. As it can be seen, the reaction time can
have a significant effect on activity. For all the catalysts, as
reaction time increases, the activity increases and after
Table 1 Activities of BIMP-Fe catalysts for polymerization of eth-
ylene and QEq charge of the catalysts
Catalyst
Activity [gr. PE/
(mmol Fe h. bar)]
QEq charge
on Fe
a
b
c
22,750
25,500
18,750
0.4511
0.4844
0.4321
Fig. 3 Effect of polymerization time on the activity. Polymerization
conditions: temperature = 30 °C, monomer Pressure = 5 bar, [Al]:
[Fe] = 1000:1, [Fe] = 0.3 9 10-3 mmol, toluene = 300 mL, stirrer
speed = 800 rmp
Polymerization conditions: ethylene pressure = 5 bar, time = 30 -
min, Toluene (solvent) = 300 mL, temperature = 30 °C, [Al]:[Fe] =
1000:1, [Fe] = 0.3 9 10-3 mmol, stirrer speed = 800 rmp
123

Novel Late Transition Metal Catalysts Based on Iron
165
resulted in decreasing Crystallinity and Mv while increas-
ing pressure decreased Crystallinity and increased Mv.
4 Conclusion
Catalysts b and c were active catalysts for polymerization
of ethylene. The para substituents dramatically influenced
the catalytic activities by changing the positive charge of
center metal, which could accelerate or decelerate the
activity of the catalysts. Higher net charge of central metal
of the catalysts raised the activity of the catalysts. Theo-
retical investigations revealed a more positive charge on
the central metal of the catalyst b, containing electron-
withdrawing group of NO2 at the para position of pyridine
ring, in comparison with the catalysts a and c, led to an
increase in activity of the catalyst c offset by lower thermal
stability and its life time.
Fig. 4 Effect of monomer pressure on the polymerization behavior.
Polymerization conditions: toluene = 300 mL, temperature = 30 °C,
Polymerization time = 60 min, [Al]:[Fe] = 1000:1, [Fe] = 0.3 9
10-3 mmol, stirrer speed = 800 rpm
Table 2 Effect of pressure and temperature on the crystallinity and
Mv
Sample
Pressure
(bar)
Temperature
(°C)
Crystallinity
(%)
Mv
Cat a
Cat a
Cat a
Cat b
Cat b
Cat b
Cat c
Cat c
Cat c
5
5
7
5
5
7
5
5
7
30
60
30
30
60
30
30
60
30
59
41
46
52
38
44
62
57
59
285,000
198,000
330,000
206,500
140,200
250,600
298,000
260,000
350,000
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reaching a maximum, it decreases. These maximums for
the catalysts a–c are around 15, 10 and 30 min, respec-
tively. In early times, the active centers of catalyst are
activated with MAO and lie easy to access for monomers
and as a result, activity increases, but with increasing of
polymerization time, the possibility of destruction of active
centers increases and leads to the decreasing of the activity.
In addition, the influence of monomer pressure between
2 and 9 bars on the catalyst behavior was studied for three
catalysts. For all the catalysts, nearly a linear plot was
obtained (Fig. 4). In the higher pressure of monomer,
the higher productivity of the catalyst was observed. The
behavior is mainly due to high concentration of the
monomer close to the catalyst active centers.
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Finally, we investigated effect of temperature and
pressure on Crystallinity and MV (viscosity average
molecular weight) (Table 2). A similar trend was discov-
ered for the polymers obtained by all the catalysts. As
anticipated, increasing temperature from 30 to 60 °C
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