Salicylaldiminato nickel(II) catalysts with 5-halo-3-methoxy groups for ethylene polymerization

Article abstract of DOI:10.1002/pola.25855

Two neutral salicylaldiminato methyl pyridine nickel(II) complexes were synthesized and evaluated for ethylene polymerization. Each catalyst bears a methoxy group in the 3-position and a halogen atom in the 5-position of the salicyl ligand, chlorine in ca

Full text of DOI:10.1002/pola.25855

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Salicylaldiminato Nickel(II) Catalysts with 5-Halo-3-methoxy Groups for
Ethylene Polymerization
Nikhil A. Kolhatkar,1 Amber M. Monfette,2 Shuo Lin,1 Massoud J. Miri1,2
1Center for Materials Science and Engineering, Rochester Institute of Technology, Rochester, New York 14623
2Department of Chemistry, Rochester Institute of Technology, Rochester, New York 14623
Correspondence to: M. J. Miri (E-mail: mjmsch@rit.edu)
Received 6 March 2011; accepted 15 November 2011; published online 13 December 2011
DOI: 10.1002/pola.25855
ABSTRACT: Two neutral salicylaldiminato methyl pyridine nick-
el(II) complexes were synthesized and evaluated for ethylene
polymerization. Each catalyst bears a methoxy group in the 3-
position and a halogen atom in the 5-position of the salicyl
ligand, chlorine in case of catalyst 3a and bromine in 3b. Mo-
lecular structures of the catalysts were obtained by X-ray crys-
tallography. The resulting polymerization activities, for
example, indicated by a maximum turnover frequency of 4,870
mol ethylene/(mol Ni ꢀ h) for 1-h runs obtained with 3a, were
higher than those of similar catalysts at comparable conditions
reported in the literature. Catalyst 3a was slightly more active
than catalyst 3b. The polymers are branched as measured by
1H NMR and 13C NMR. This was also reflected in the melting
temperatures between 76 and 113 ꢁC obtained by differential
scanning calorimetry. By using gel permeation chromatogra-
phy measurements, it was determined that the Mw of the poly-
mers ranges between about 5,400 and 21,600 g/mol. In
particular, the effect of the polymerization temperature on the
catalyst activity, degree of branching, and molecular weight
C
V
properties has been described. 2011 Wiley Periodicals, Inc. J
Polym Sci Part A: Polym Chem 50: 986–995, 2012
KEYWORDS: branched; catalysis; nickel; polyethylene (PE); sin-
gle-site catalysts
INTRODUCTION Single-site catalysts provide excellent con-
trol over polymerization kinetics and resulting polymer
properties. The earlier developed metallocene catalysts pos-
sess mainly zirconium or titanium centers and can be used
for polymerization of hydrocarbon monomers. However, late
transition metal catalysts have been shown to be more stable
in the presence of polar monomers or solvents.1–7 In addi-
tion, the latter catalysts can be used as single-component
catalysts, that is, without the use of a cocatalyst or scavenger.
Furthermore, these catalysts can cause branching via chain
walking, which can be used for additional applications, such
as for the production of branched and hyperbranched poly-
ethylene and similar polymers with other topologies.8–11
merization.10,11 When methyl acrylate was applied as como-
nomer with ethylene, insertion copolymerization did not
occur unless a palladium analog was used.1 The influence of
changes in the structure of the nickel-based catalyst was fur-
ther studied by other research groups mainly focusing on
the analysis of the resulting type of branching.13,14 Other fea-
sible late transition metal catalysts with iron as the coordi-
native metal and a bisiminopyridyl ligand have been devel-
oped for the polymerization of ethylene; however, attempts
to use methylacrylate as a comonomer besides ethylene led
to blends of the homopolymers.15,16
Salicylaldiminato groups were initially introduced by Grubbs
and coworkers as ligands with nickel(II) complexes.17–19 The
salicylaldiminato nickel(II) complexes were highly active in
the polymerization of ethylene even when polar compounds
such as water were present.18 They also have the ability to
incorporate moderately polar monomers, particularly norbor-
nene derivatives. Catalysts were more active when triphenyl-
phosphine was not applied as ligand. In addition, it was
shown that bulky ligands on the salicyl ring resulted in poly-
mers with higher molecular weights. As with the nickel dii-
mine catalysts, these catalysts tend to polymerize according
to a chain walking mechanism resulting in branched polyeth-
ylene.17–19 These types of catalysts were also applied with
Late transition metal polymerization catalysts originate from
the SHOP (shell high olefins process) catalysts,12 which are
chelated complexes of nickel. Oligomerization could be
diminished in favor of polymerization by changing ligand
groups, which results in a reduction of the rate of b-H-elimi-
nation relative to monomer insertions. The first polymeriza-
tion catalysts based on the SHOP catalyst contained smaller
chelated ligands, which led to moderate activities.5–7 As
shown initially by Brookhart and coworkers, a series of pri-
marily nickel catalysts with a-diimine ligands that contained
bulky aromatic groups were very active for ethylene poly-
Additional Supporting Information may be found in the online version of this article.
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SCHEME 1 Formation of the 5-chloro-3-methoxy salicylaldiminato methyl pyridine nickel (II) catalyst and its bromo analog used
for ethylene polymerization, 3a and 3b, respectively.
methylaluminoxane as cocatalyst using early transition metals
in the so-called FI (phenoxy-imine) catalysts20,21 as well as
with nickel-based analogs.22 Many other research groups have
developed other nickel-based catalysts with salicylaldiminato
ligands.23–33
The structure of catalyst 3b is quite similar to that of cata-
lyst 3a. Both types of catalyst crystals are isomorphic, having
triclinic structures. The ligand coordination around the
nickel center is close to square planar. As a result of the dif-
ference in the halogen atoms, the bond length XAC is larger
for the bromo compound, 1.903 Å, versus 1.750 Å for the
chloro compound. Consequently, the dimensions and angles
The primary objective of the research performed was to find
a catalyst that would be economical as a single component
and involve minimal steps in its synthesis. In addition, a
high polymerization activity and a reasonable range of mo-
lecular weight properties were also desired. The use of a sal-
icylaldiminato nickel(II) catalyst with chlorine or bromine in
the 5-position and a methoxy group in the 3-position was
investigated to obtain some of the aforementioned desirable
properties.34 The catalyst’s main ligand is formed via a Schiff
base reaction, which then reacts with (tmeda)NiMe2 in a
subsequent step to form the catalyst as shown in Scheme 1
as 3a and 3b. As originally suggested by Klabunde and Ittel,6
pyridine is applied as a lightly bonded ligand instead of the
frequently applied triphenylphosphine. The use of a cocata-
lyst or scavenger was not necessary.
RESULTS AND DISCUSSION
Catalyst Structure
The X-ray crystallograms for catalyst 3a are shown in Figure 1.
In Table 1 the crystallographic data are given.
Selected bond lengths and bond angles are summarized in
Table 2.
FIGURE 1 Molecular structure of the catalyst complex 3a (H-
atoms are not shown for simplicity).
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TABLE 1 Crystallographic Data and Structure Refinements for 3a and 3b
3a
3b
Empirical formula
Formula weight
Temperature (K)
C26H31ClN2NiO2
497.69
C26H31BrN2NiO2
542.15
100.0
100.0
˚
Wavelength (A)
0.71073
0.71073
Crystal system
Space group
Triclinic
Triclinic
P-1
P-1
˚
a (A)
8.8179(8)
8.7980(11)
11.2992(14)
13.5872(17)
73.430(2)
˚
b (A)
11.22289(10)
13.4483(12)
74.098(2)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
76.925(2)
77.323(2)
82.990(2)
83.442(2)
˚
V (A)
1244.86(19)
2
1261.1(3)
Z
2
qcalculated (mg/m3)
Abs. coeff. (mmꢂ1
F(000)
1.328
1.428
)
0.911
2.378
524
560
Crystal color, morphology
Orange, block
0.22 ꢀ 0.20 ꢀ 0.16
1.89–35.63
27,779
Orange, block
0.24 ꢀ 0.22 ꢀ 0.18
1.59–35.63
27,938
Crystal size (mm)
y range (ꢁ)
No. of reflections
Independent reflections
No. of data/restraints/param.
Goodness of fit on F2
R indices [I>2sigma(I)]
R indices (all data)
11,280 [R(int) ¼ 0.0360]
11,280/0/295
1.015
11,416 [R(int) ¼ 0.0325]
11,416/0/295
1.020
R1¼0.0373, wR2 ¼ 0.0867
R1¼0.0550, wR2 ¼ 0.0947
0.550, ꢂ0.260
R1¼0.0333, wR2 ¼ 0.0755
R1¼0.0564, wR2 ¼ 0.0831
0.684, ꢂ0.299
3
˚
Largest diff. peak, hold (e/A )
of the unit cells are also different, as also indicated by the
data in Table 1. In comparison to similar salicylaldiminato
nickel(II) catalysts bearing triphenylphosphine groups
instead of pyridine as ligand, the NiAN(1) bond is shorter
with 1.8841(1) Å compared with 1.937(4) Å in ref. 20 and
1.932(3) Å in ref. 30. However, the length of the NiAO1 bond
is very similar to those reported in these references. Further
details on the crystallographic data, bond lengths and bond
angles are provided in the available Supporting Information.
these catalysts are higher than those reported for a compara-
ble catalyst with two iodine atoms in the 3- and 5-positions
at similar conditions as reported by Mecking and co-
workers.23,24 In a polymerization run with a 3,5-diiodosalicy-
laldiminate methyl pyridyl nickel(II) catalyst synthesized
according to the literature,24 a TOF of 1970 mol PE/(mol Ni
ꢀ h) was obtained using similar reaction conditions to that
of Entry 1. When compared with 3a under the same condi-
tions, the 3,5-diiodosalicylaldiminate methyl pyridyl nick-
el(II) catalyst had less than half the activity (using 351
lmol/L at 60 ꢁC, 3.83 g polymer was obtained in 1 h; Mw
13,600 g/mol and Mw/Mn ¼ 2.30). Activities reported for a
salicylaldiminato nickel catalyst with a methoxy group in the
5-position were also lower than those with 3a and 3b.18
Polymerization Behavior
In Table 3 the conditions, yields, and resulting activities for
the polymerization of ethylene are shown.
The turnover frequencies (TOFs) are relatively high consider-
ing that only 7.6 bar ethylene was applied. The chloro analog
catalyst (3a) is slightly more active than the bromo counter-
part (3b), as can be determined by the 1-h runs at the same
polymerization temperatures of 30 and 60 ꢁC. This effect is
likely due to the higher electronegativity of the chlorine com-
pared with bromine. Electron-withdrawing substituents in
the 5-position lead to an increase in activity as had been al-
ready stated by Grubbs and coworkers.18 The TOFs with
Figure 2 shows the polymerization activity measured from
ꢁ
the consumption of ethylene versus the run time at 60 C. It
is apparent that the catalyst is most active in the first 15
min of the polymerization with a maximum of 20,500 mol
C2H4/(mol Ni ꢀ h), and that its activity steadily decreases as
the run progresses. However, even after an hour polymer
still being is produced, although at about one-tenth of the
initial rate [about 2,100 mol C2H4/(mol Ni ꢀ h)]. The slight
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TABLE 2 Selected Bond Lengths and Angles for Complexes 3a
and 3b
Polyethylene Properties
In Table 4 some characteristic properties of the polymers
produced are given.
˚
Bond Lengths (A)
Bond Angles (ꢁ)
The degree of branching was determined by examining the
intensity of the doublet of the methyl group in the 1H NMR
spectra observed at about 0.85 ppm. The doublet is caused
by the coupling of the methyl protons with the methine pro-
tons, the latter having a peak at about 1.05 pm. The 13C
NMR spectra of these polymers resemble those of other
branched polyethylene that has been produced with similar
nickel catalysts that cause the branching due to chain
walking.29,35
Catalyst 3a
NiAN1
NiAO1
NiAN2
NiAC1
ClAC5
1.8841(10)
N1ANiAO1
93.60(4)
170.39(4)
84.79(4)
1.9030(9)
N1ANiAN2
O1ANiAN2
N1ANiAC1
O1ANiAC1
N2ANiAC1
C8AO1ANi
C7AO2AC9
C2AN1AC15
C2AN1ANi
C15AN1ANi
C4AC5ACl
C6AC5ACl
1.9054(10)
1.9320(13)
1.7499(12)
1.2891(14)
1.3537(14)
1.4295(15)
1.3093(15)
1.4476(15)
93.63(5)
169.91(5)
89.21(5)
O1AC8
O2AC7
O2AC9
N1AC2
N1AC15
128.86(8)
116.86(10)
112.45(9)
124.82(8)
122.13(7)
119.79(9)
118.05(9)
In Figure 4, tꢁhe 13C NMR spectra of two samples produced
at 40 and 60 C are shown.
The applied peak assignments were previously published in
the literature.29,35,36 The presence of short-chain branching
up to hexyl groups can be detected. The longer alkyl groups
present are all even numbered (ethyl, butyl, and hexyl
groups). However, methyl groups (B1) represent the domi-
nant type of alkyl groups found in the polymer. 13C NMR
permits differentation by the length of the branches present.
Using the two polymers shown in Figure 4, the following
normalized intensities were obtained (Table 5).
Catalyst 3b
NiAN1
NiAO1
NiAN2
NiAC1
1.8834(11)
1.9025(9)
N1ANiAO1
N1ANiAN2
O1ANiAN2
N1ANiAC1
O1ANiAC1
N2ANiAC1
C8AO1ANi
C7AO2AC9
C2AN1AC15
C2AN1ANi
C15AN1ANi
C4AC5ABr
C6AC5ABr
93.69(4)
170.46(5)
84.83(4)
1.9033(11)
1.9302(13)
1.9028(13)
1.2854(15)
1.3548(16)
1.4231(17)
1.3090(16)
1.4433(16)
93.48(5)
Based on the data in Table 5, the number of total methyl
groups per 1000 C atoms for the polymers produced at 40
and 60 ꢁC was calculated to be 24 and 53%, respectively,
which is in good agreement with the corresponding data
BrAC5
170.15(5)
89.19(5)
O1AC8
O2AC7
O2AC9
N1AC2
N1AC15
128.87(8)
117.12(11)
112.64(11)
124.55(9)
122.31(8)
119.77(10)
118.16(10)
1
obtained from the H NMR spectra, shown in Table 4. It was
also determined that the ratio of methyl groups (B1) to the
longer alkyl groups (C1-C2, D1-D4, and E1-E6) at 40 ꢁC is
almost 5, whereas at 60 ꢁC the ratio is closer to 2. The
increase of the longer alkyl chains at higher temperature is
due to the enhanced chain walking. In contrast to LDPE pro-
duced by radical polymerization, which involves chain trans-
fer to the polymer, the present polyethylene has a much
higher intensity of methyl groups and a lower intensity of
the longer alkyl. No peaks indicating any unsaturated inter-
nal or terminal groups could be detected.
fluctuations in the rate are due to changes in the polymeriza-
tion temperature of 63 ꢁC around the target temperature
and the corresponding changes of the solubility of ethylene
in the applied solvent, toluene.
The polymers produced at 60 and 70 ꢁC are slightly trans-
parent and rubbery. The degree of branching increases with
temperꢁature exponentially over the temperature range of
30–70 C as shown in Figure 5. This corresponds to a higher
rate of chain transfers by b-H-elimination with increasing
temperature.
The dependence of the activity in terms of the TOF of the
polymerization versus temperature for the 1-h runs is shown
in Figure 3. It is not surprising that the activity increases as
the temperature rises from 30 to 50 ꢁC, as this is typical
behavior for many polymerizations applying single-site cata-
lysts. However, the activity appears to reach a maximum
between 50 and 60 ꢁC after which it decreases, as can be
verified with the 15-min runs. This type of dependence of
the polymerization activity on temperature is consistent with
the observations made previously about several different
types of nickel-based catalysts.30,31 The mechanism of the
deactivation of this catalyst is not yet known. A similar deac-
tivation was also observed with a nickel 2-iminopyridine N-
oxide catalyst in ethylene polymerization.31 To a smaller
degree, the lower solubility of ethylene at higher tempera-
tures may also cause a decrease in polymerization activity.
In Figure 6, the differential scanning calorimetry (DSC) dia-
grams of two polyethylene samples obtained with catalyst
3b are shown. The polyethylene produced at 30 ꢁC is more
crystalline and has a melting temperature that is about
32 ꢁC higher than the polyethylene produced at 70 ꢁC. The
peak of the more crystalline polyethylene is more pro-
nounced because of the presence of relatively few branches,
whereas the melting peak of the more amorphous polyethyl-
ene is much broader. The crystallization peak of the more
amorphous polymer is almost 35 ꢁC lower that of its more
crystalline counterpart. The gap between the crystallization
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TABLE 3 Polymerization Conditions, Polymer Yields, and Turnover Frequencies
TOF [mol
Entry No.
Catalyst Type
[Catalyst] (l mol/L)
Tp (ꢁC)
tp (min)
Yield (g)
C2H4/(mol Ni ꢀ h)]
1
3a
3a
3a
3a
3a
3a
3b
3b
3b
3b
3b
3b
3b
3b
3b
3b
50
101
157
282
302
322
308
310
332
314
326
462
332
327
328
332
60
60
60
60
30
30
30
40
40
50
50
60
60
60
70
70
60
60
60
60
60
60
60
60
15
60
15
60
60
15
60
30
1.27
2.51
4.28
4.01
0.40
0.46
0.15
0.45
0.46
6.15
3.05
6.00
5.40
3.65
4.85
4.90
4,510
4,460
4,870
3,390
240
2
3
4
5
6
140
7
90
8
260
9
990
10
11
12
13
14
15
16
3,500
6,690
2,320
2,900
7,980
2,630
5,270
Ethylene pressure: 7.6 bar; solvent: toluene; total volume: 200 mL
(except Entry 4 with 150 mL).
temperature and the melting temperature is also higher for
with radical initiators or mLDPE (metallocene based LDPE)
obtain with constrained geometry metallocene catalysts.
ꢁ
the more amorphous polymer with a gap of 16.76 C versus
ꢁ
12.75 C.
The molecular weights of the polymers are relatively low,
because a moderate ethylene pressure (7.6 bar) was used
and the substitutents on the salicyl ring are not bulky. Due
to its larger size relative to a hydrogen or halogen atom, the
presence of the methoxy group in the 3-position may have
only caused a slight increase in molecular weight, comparing
about 15,000 g/mol for both 3a and 3b (Entries 4 and 13,
respectively) with 13,600 g/mol obtained using the afore-
mentioned 3,5-diiodo salicylaldiminato nickel catalyst. The
molecular weight moderately decreased when the catalyst
concentration was increased (Entries 1–4), which is the
The reported glass transition temperatures do not necessarily
represent the only secondary transitions of the polymers, but
rather those that could be observed by the applied DSC tech-
nique. They are also indicative of the highly branched struc-
ture of the polymers. The dependence of the melting temper-
ature on the degree of branching is shown in Figure 7. As
expected, the crystallinity of the polymers decreases as the
degree of branching increases. The correlation of the melting
temperatures of the polymers with their degree of branching
is quite good (R2 close to 90%) with the maximum melting
point of 137.5 ꢁC for the curve extrapolated to zero branch-
ing. The polymers have lower melting points than is typical
for low density polyethylene (LDPE) type polymers formed
FIGURE 3 Turnover frequency versus polymerization tempera-
ture (1-h runs with 3b).
FIGURE 2 Turnover frequency as a function of polymerization
time (with 3a, Entry 2).
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TABLE 4 Degree of Branching, Molecular Weight Properties, and Transition Temperatures
Branches per
1,000 C-Atomsa
b
b
Tc (ꢁC)
b
Tg (ꢁC)
c
c
Entry No.
Tp (ꢁC)
Tm (ꢁC)
Mw (g/mol)
Mw/Mn
1
60
60
60
60
30
30
30
40
40
50
50
60
60
60
70
70
51
57
51
64
28
31
27
24
27
48
41
55
52
69
74
72
88
88
71
73
73
64
99
99
99
94
90
83
88
74
82
76
58
64
ꢂ54
ꢂ57
ꢂ53
ꢂ60
n.d.
n.d.
n.d.
n.d.
n.d.
ꢂ33
ꢂ25
ꢂ40
ꢂ63
ꢂ60
ꢂ63
ꢂ63
15,200
14,600
14,900
12,600
6,700
2.07
2.07
1.90
1.83
1.60
1.64
1.40
1.29
1.50
1.60
2.30
2.96
1.76
2.10
3.30
2.02
2
3
90
4
76
5
113
112
113
108
105
98
6
7,000
7
5,400
8
11,000
11,300
21,600
17,400
14,900
14,000
12,000
8,700
9
10
11
12
13
14
15
16
96
91
91
87
76
81
9,700
n.d., not detected.
a
Determined by 1H NMR.
By DSC.
b
c
Determined by GPC with polyethylene apparent molecular weights.
normal behavior observed with most polymerization initia-
tors. In the 15-min runs (Entries 9, 11, and 14), similar mo-
lecular weights were obtained as in the 1-h runs, indicating
that the polymerizations are not living, even below 50 C. In
fact, all determined properties of these polymers obtained in
the shorter runs, including the degree of branching and tran-
sition temperatures, are quite similar to those in the 1-h
runs. As is typical for single-site catalysts, the polydispersity
indexes are mostly close to 2. The deviations of the PDI from
2 (min. ꢂ0.7 and max. þ1.3) for the runs at different tem-
peratures do not indicate a systematic trend but are similar
to those obtained with other nickel (II) catalysts.11,31
ꢁ
13
FIGURE 4 C NMR spectra of polymers obtained at different temperatures: (a) 60 ꢁC (Entry 13) and (b) 40 ꢁC (Entry 8) with 3b.
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TABLE 5 Normalized Peak Intensities for Polymers Produced at 40 and 608C with 3b
Peak Label
A10
A2
A20, E1
A1
A4
A5
A3-E2
D3, E5
B1
D4, D6
C2
60ꢁC (Entry 12)
Int. (%)
40ꢁC (Entry 9)
0.373
0.148
5.55
3.71
2.55
2.78
1.90
11.1
65.2
79.1
7.22
4.51
0.611
0.240
3.14
1.85
0.846
0.223
0.520
0.162
Int. (%)
0.807
7.33
In Figure 8, the dependence of the weight-average molecular
weight on the polymerization temperature is shown for the
1-h runs with 3b.
Synthesis of Catalysts
The ligands and catalysts were synthesized using similar
methods to previously published procedures by Grubbs and
coworkers and Bauers and Mecking.17,23
The variation of the molecular weight with temperature is
peculiar because it goes through a maximum at 50 ꢁC. The
molecular weight increases between 30 and 50 ꢁC, because
the rate of polymerization also increases (Mn ꢃ kp) in that
temperature range, as already shown in Figure 2. The
decrease of the molecular weight above 50 ꢁC is observed
with most coordinative polymerization catalysts and is due
to the overcompensating increase in chain transfers via b-H-
elimination. Similar observations of the presence of a maxi-
mum or plateau of the molecular weight with increasing po-
lymerization temperature were made with other nickel-based
catalysts used for olefin polymerization.25,28,37
Ligands 2a and 2b
A suspension of 1 g (5.4 mmol) of 5-chloro-2-hydroxy-3-
methoxybenzaldehyde (1a) and 10 mL of methanol was pre-
pared at room temperature (RT). In the case of ligand 2b,
1 g (4.3 mmol) was used. A solution of 2 g or 2.63 mL (11.3
mmol) of diisopropylaniline in 15 mL methanol with one to
two drops of formic acid was slowly added through a drop-
funnel, turning the yellow solution to orange. The mixture
was heated for about 30 min to 50 ꢁC and then stirred for
24 h at RT. The mixture was left in the freezer at about ꢂ20
ꢁC for another 24 h until the ligand had crystallized. The
mixture was filtered and washed with cold methanol. 0.836
g (44.8%) yellow solid 2a and 0.729 g (43.5%) yellow solid
2b were obtained.
EXPERIMENTAL
Materials
1
Ligand 2a: H NMR (300 MHz, CDCl3): 13.67 (s, 1H), 8.29 (s,
All chemicals were obtained from Sigma Aldrich, except for
(tmeda)NiMe2, which was purchased from MCAT GmbH, Ger-
many (tmeda: N,N,N0,N0-tetramethylethylenediamine) and the
ethylene, which was obtained from Matheson. Reagents for the
ligand synthesis were used without further purification. All
operations involving the catalyst syntheses and polymerizations
were conducted under argon using dried solvents. Toluene,
diethyl ether, and pentane were dried over sodium/benzophe-
none; in the case of the latter two solvents, tetraglyme (tetra-
ethylene glycol dimethyl ether) was added, and the solvents
were distilled. Anhydrous pyridine was degassed before use.
1H), 7.31 (s, 1H), 7.02 (s, 2H), 4.03 (s, 3H, AOCH3), 3.02
(sep, 2H, J ¼ 6.9 Hz, ACH(CH3)2), 1.61 (s, 1H), 1.23, (d, 12
H, J ¼ 6.8 Hz, ACH(CH3)2); 13C NMR (75 MHz, CDCl3): 166.2,
150.7, 149.8, 145.8, 139.1, 126.3, 123.8, 119, 115.3, 56.8,
23.9. ELEM. ANAL. calcd for C20H24NO2Cl: C, 69.45; H, 6.99; N,
4.05. Found: C, 69.27; H, 7.02; N, 4.03.
1
Ligand 2b: H NMR (300 MHz, CDCl3): 13.70 (s, 1H), 8.28 (s,
1H), 7.31 (s, 1H), 7.16 (s, 2H), 4.01 (s, 3H, AOCH3), 3.01
(sep, 2H, J ¼ 7.0 Hz, ACH(CH3)2), 1.61 (s, 1H), 1.22 (d, 12 H,
J ¼ 7.2 Hz, ACH(CH3)2); 13C NMR (75 MHz, CDCl3): 166.0,
151.2, 150.0, 145.8, 139.1, 126.3, 125.9, 123.8, 120.0, 118.0,
110.4, 56.8, 28.6, 23.9. ELEM. ANAL. calcd for C20H24NO2Br: C,
61.54; H, 6.20; N, 3.59. Found: C, 61.45; H, 6.24; N, 3.55.
Catalysts 3a and 3b
Four hundred milligrams (1.95 mmol) of [(tmeda)Ni(CH3)2]
was added to a solution of 670 mg (1.94 mmol) of 5-chloro-
3-methoxysalicylaldimine ligand (2a) in about 15 mL of dry
diethyl ether containing 1.56 mL (19.4 mmol) pyridine at
ꢁ
about ꢂ25 C. In case of 3b, 226 mg (1.10 mmol) [(tmeda)-
Ni(CH3)2], 424 mg (1.09 mmol) 2b, and 0.88 mL pyridine
were used. The yellow ligand solution turned dark red.
Within 30 min, the mixture was brought to RT and kept stir-
ring for 5 h. The red solution was then filtered over Celite
and washed with ether. The ether was evaporated and about
50 mL cold pentane was added to the residue. The solution
ꢁ
FIGURE 5 Dependence of degree of branching on polymeriza-
tion temperature (1-h runs with 3b).
was kept at ꢂ20 C for 2–4 days for crystallization. The pen-
tane then was removed and the solid catalyst was isolated.
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FIGURE 6 DSC diagrams of polyethylene produced at 30 ꢁC (top) and at 70 ꢁC (bottom) with 3b (Entries 7 and 16, respectively).
FIGURE 8 Dependence of weight-average molecular weight
FIGURE 7 Melting temperatures versus degree of branching
and polydispersity on polymerization temperature (1-h runs
(all runs).
with 3b).
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0.605 g (62.4%) red solid 3a and 0.383 g (64.9%) red/
brown solid 3b were obtained.
tion temperature of between 50 and 60 ꢁC. As indicated by
13C NMR spectroscopy and thermal transitions, the obtained
polymers contain short and long branching causing their
crystallinities to be lower than linear polyethylene. The type
of branching with dominant methyl groups is typical for
polyethylene produced by a chain walking mechanism. The
degree of branching increases continually with increasing po-
lymerization temperature. Molecular weights reach a maxi-
1
Catalyst 3a: H NMR (300 MHz, CDCl3): 7.07 (d, 2H, J ¼ 7.7
Hz), 6.5 (s,1H), 6.27 (s, 1H), 4.38 (sep, 2H, J ¼ 6.7 Hz,
ACH(CH3)2), 3.17 (s, 3H, AOCH3), 1.35 (d, 6H, J ¼ 7.1 Hz,
ACH(CH3)2), 1.21 (d, 6H, J ¼ 6.7 Hz, ACH(CH3)2); 13C NMR
(75 MHz, CDCl3): 142.5, 126.3, 123.5, 121.5, 113.3, 55.2,
29.4, 25.0, 23.8. ELEM. ANAL. calcd for C26H31N2O2ClNi: C,
62.75; H, 6.28; N, 5.63. Found: C, 62.12; H, 6.32; N, 5.56.
ꢁ
mum at close to 50 C.
This work was partially funded by the Xerox University Affairs
Committee grant. The authors thank Dr. Hadi Mahabadi and
Dr. Guerino Sacripante of Xerox Research Centre Canada for
their support. We also thank Dr. Peter Nickias and Dr. Daniel
Harrington of DOW Chemical Co. for providing the GPC data,
and Dr. William Brennessel of the University of Rochester for
the X-ray crystallography reports.
1
Catalyst 3b: H NMR (300 MHz, CDCl3): 7.09 (d, 2H, J ¼ 7.7
Hz), 6.67 (s, 1H), 6.38 (s, 1H), 4.38 (sep, 2H, J ¼ 6.8 Hz,
ACH(CH3)2), 3.19 (s, 3H, AOCH3), 1.36 (d, 6H, J ¼ 6.5 Hz,
ACH(CH3)2), 1.22 (d, 6 Hz, J ¼ 6.8 Hz, ACH(CH3)2); 13C
NMR (75 MHz, CDCl3): 164.0, 142.4, 126.2, 124.9, 123.5,
115.8, 55.2, 29.4, 25.0, 23.8. ELEM. ANAL. calcd for
C
26H31N2OBrNi: C, 57.60; H, 5.76; N, 5.17. Found: C, 57.18;
H, 5.59; N, 5.18.
Polymerizations
REFERENCES AND NOTES
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