Ethylene polymerization with nickel complexes containing aminophosphine ligands

Article abstract of DOI:10.1016/j.molcata.2006.05.040

Bis(aminophosphines) were prepared by reaction of the corresponding diamines with chlorodiphenylphosphine. As phosphines are readily oxidized to pentavalent phosphorus forming P{double bond, long}O bonds, the analogous bis(aminophosphine oxide) were also synthesized. These bis(aminophosphines) and their products of air oxidation were employed to prepare the nickel complexes I, II, III and IV by reaction of dimethoxyethane nickel dibromide adduct and the bis(aminophosphorus) compounds in THF, at room temperature. The new Ni complexes activated by methylaluminoxane (MAO) were active as catalysts for ethylene polymerization. The influences of Al/Ni ratio and polymerization temperature on the catalyst activity, as well as on the polymer microstructure, were investigated. Highest yield was obtained at Al/Ni ratio = 2000. The more flexible aminophosphine complex II showed the highest catalytic activity. The temperature influence on polymerization reaction present a peculiar behavior: at low temperatures the oligomer production was higher and yield of polymer was lower. At temperatures bellow zero, octene and/or its isomers were formed predominantly. The polyethylenes obtained by polymerization with aminophosphine complexes I and II presented molecular weight even higher than 200,000 as well as broad molecular weight distribution. ¹³C NMR analyses indicated that they were branched polymers with the melting temperature (T_m) in the range of 117-127 °C. The complexes containing the oxidized ligands (III and IV) produced more linear polyethylenes with T_m around 130 °C.

Full text of DOI:10.1016/j.molcata.2006.05.040

Journal of Molecular Catalysis A: Chemical 258 (2006) 267–274
Ethylene polymerization with nickel complexes containing
aminophosphine ligands
Mauro C.B. Dolinskya, Whei O. Lina, Marcos L. Diasb,∗
a Departamento de Qu´ımica, Instituto Militar de Engenharia, Prac¸a Tiburcio, 80, 22290-270 Rio de Janeiro, RJ, Brazil
b Instituto de Macromole´culas Professora Eloisa Mano, Universidade Federal do Rio de Janeiro, CP. 68525, 21945-970 Rio de Janeiro, RJ, Brazil
Received 26 September 2005; received in revised form 12 May 2006; accepted 16 May 2006
Available online 7 July 2006
Abstract
Bis(aminophosphines) were prepared by reaction of the corresponding diamines with chlorodiphenylphosphine. As phosphines are readily oxi-
dized to pentavalent phosphorus forming P O bonds, the analogous bis(aminophosphine oxide) were also synthesized. These bis(aminophosphines)
and their products of air oxidation were employed to prepare the nickel complexes I, II, III and IV by reaction of dimethoxyethane nickel dibromide
adduct and the bis(aminophosphorus) compounds in THF, at room temperature. The new Ni complexes activated by methylaluminoxane (MAO)
were active as catalysts for ethylene polymerization. The influences of Al/Ni ratio and polymerization temperature on the catalyst activity, as well
as on the polymer microstructure, were investigated. Highest yield was obtained at Al/Ni ratio = 2000. The more flexible aminophosphine complex
II showed the highest catalytic activity. The temperature influence on polymerization reaction present a peculiar behavior: at low temperatures the
oligomer production was higher and yield of polymer was lower. At temperatures bellow zero, octene and/or its isomers were formed predominantly.
The polyethylenes obtained by polymerization with aminophosphine complexes I and II presented molecular weight even higher than 200,000 as
well as broad molecular weight distribution. 13C NMR analyses indicated that they were branched polymers with the melting temperature (Tm) in
the range of 117–127 ◦C. The complexes containing the oxidized ligands (III and IV) produced more linear polyethylenes with Tm around 130 ◦C.
© 2006 Published by Elsevier B.V.
Keywords: Ethylene; Polymerization; Nickel catalyst; Aminophosphine ligands; Oligomerization
1. Introduction
characteristics: the donor effect of the electron pair of phospho-
rus atom and the use empty d orbital of the phosphorus atom to
stabilize the metal–phosphorus bond, once the orbital 3p and 3d
are close in the diagram of energy [12–16]. The literature has
already reported examples in which complexes bearing biden-
tate phosphine ligands also produce branched polyethylenes in
high yields, depending on the polymerization condition [17,18].
Thus, bidentate phosphorus-containing complexes can be poten-
tial ligands for good olefin polymerization catalysts if adequate
steric hindrance is present around Ni atoms. Here we report
the synthesis of Ni complexes with bis(aminophosphine) and
bis(aminophosphine oxides) ligands and application of these
compounds in ethylene polymerization.
Ethylene polymerization using diimine complex catalysts
based on late transition metals such as nickel II and palladium
II was reported by Brookhart and coworkers [1–11]. The bulky
bidentate diimine ligands in those complexes are the key fac-
tor for the production of high molecular weight polymers. In
addition, these catalysts are able to produce highly branched
polyethylenes without using comonomers, such as 1-hexene or
1-octene. The Ni–nitrogen bond in the diimine complexes are
stable enough to avoid removal of the bulky ligand during cat-
alyst activation by the aluminum cocatalyst and the bulky aryl
rings in the axial sites of the square plane Ni complex retard
the rate of chain transfer, as result obtaining high molecular
weight polyethylenes. Bidentate diphosphine compounds have
tendency to form stable nickel complexes due to the following
2. Experimental
2.1. Materials and general conditions
∗
4-(Dimethylamino)pyridine and chlorodiphenylphosphine
Corresponding author. Tel.: +55 21 562 7221; fax: +55 21 270 1317.
E-mail address: mldias@ima.ufrj.br (M.L. Dias).
were used as received. Tetrahydrofuran and n-pentane were
1381-1169/$ – see front matter © 2006 Published by Elsevier B.V.
doi:10.1016/j.molcata.2006.05.040

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M.C.B. Dolinsky et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 267–274
purified by reflux with sodium/potassium alloy. Ethyl ether
was purified by reflux with sodium/potassium alloy follow-
ing LiAlH4 treatment. Toluene was purified by treatment with
P2O5 following by reflux with sodium/potassium alloy. Triethy-
lamine and 1,2-ethylenediamine were purified by distillation.
1,2-Diaminebenzene was purified by sublimation. All the opera-
tions related to phosphorus complexes preparation were carried
out under an argon atmosphere using standard Schlenk tech-
niques. The complex was prepared according to literature [19].
The ligands were prepared modifying the methodology previous
described in literature [20] as described below (Fig. 1).
times with 50 ml of diethyl ether, giving of a white powder. IR
(KBr disc, cm−1) 835; 1108; 1433; 1480; 1602; 2857; 2921;
3047; 3288. NMR (CDCl3) 31P δ: 42.2; 1H δ: 7.2–6.35 (m, 20H,
arom); 2.96–2.99 (m, J = 7.5, 4H, CH2); 2.1 (s, 2H, NH); 13C δ:
65.0 (s, Caliph); 68.0 (s, Caliph); 114.5 (s, Car); 128.2 (s, Car);
128.5 (s, Car); 131.1 (s, Car); 131.4 (s, Car); 174.0 (s, Car). Mass
spectrum (m/z): 428 (M+), 243 (61%), 230 (76%), 201 (100%).
2.2.3. Synthesis of N,Nꢀ-bis(diphenylphosphoryl)-
1,2-phenylenediamine
To a solution of 12.25 g (0.020 mol) of 1,2-phenylenedia-
mine, 3 ml of triethylamine and 100 mg of 4-(dimethylamino)
pyridine in 50 ml of dry tetradydrofuran were added dropwise to
a solution containing 7.5 ml (0.04 mol) of chlorodiphenylphos-
phine in 50 ml of tetrahydrofuran. After 3 h of intense stirring
at room temperature, the solution was filtered and the residue
washed with tetradydrofuran. The filtrate was evaporated and
the light brown oil was washed three times with 50 ml of diethyl
ether, giving a brown powder. IR (KBr disc, cm−1) 899; 1114;
2.2. Synthesis of ligands
2.2.1. Synthesis of N,Nꢀ-bis(diphenylphosphine)-
1,2-phenylenediamine
To a solution of 1.45 g (0.013 mol) of 1,2-phenylenediamine,
3.7 ml of triethylamine and 100 mg of 4-(dimethylamino)pyri-
dine in 50 ml of dry tetrahydrofuran were added dropwise to a
solution containing 4.9 ml (0.0268 mol) of chlorodiphenylphos-
phine in 50 ml of tetrahydrofuran. After 3 h of intense stirring
at room temperature, the solution was filtered through a sin-
tered Schlenk and the residue washed with THF. The filtrate
was evaporated and then the light brown oil was washed three
times with 50 ml of diethyl ether, giving 2.75 g of a light brown
powder (yield, 43%). Mp. 82–85 ◦C. IR (KBr disc, cm−1) 905;
1161; 1436; 1479; 3244. NMR (CDCl3) 31P δ: 253.27; H δ:
1
6.76–7.59 (m, 24H, CH arom); 4.3 (s, 2H, NH). Mass spectrum
(m/z): 508 (M+), 290 (100%), 201 (62%), 183 (55%).
2.2.4. Synthesis of
N,Nꢀ-bis(diphenylphosphoryl)-1,2-ethylenediamine
To a solution of 1.2 g (0.02 mol) of 1,2-ethylenediamine,
5.6 ml of triethylamine and 100 mg de 4-(dimethylamine)pyri-
dine in 50 ml of dry tetrahydrofuran were added dropwise to
a solution containing 7.3 ml (0.04 mol) of chlorodiphenylphos-
phine in 100 ml of tetrahydrofuran. After 3 h of intense stirring,
at room temperature, the solution was filtered and the residue
washed with tetradydrofuran. The filtrate was evaporated and
the light brown oil was washed three times with 50 ml of diethyl
ether, giving a light yellow powder. IR (KBr disc, cm−1) 886;
1098; 1292; 1433; 1493; 1594; 3067; 3335. NMR (CDCl3) 31
P
δ: 33.2; 1H δ: 6.79–6.83 (m, 2H, CH arom); 7.06–7.09 (m, 2H,
CH arom); 7.27–7.39 (m, 20H, CH arom); 4.27 (d, J = 7.75 Hz,
2H, NH); 13C δ: 131.2 (s, Car); 130.9 (s, Car); 128.9 (s, Car);
128.4 (s, Car); 121.9 (s, Car); 119.7 (s, Car); 119.5 (s, Car). Mass
spectrum (m/z) 476 (M+), 290 (100%), 213 (79%), 183 (81%),
137 (95%).
2.2.2. Synthesis of N,Nꢀ-bis(diphenylphosphine)-
1,2-ethylenediamine
1090; 1124; 1185; 1436; 1479; 1586; 3225. NMR (CDCl3) 31
δ: 114.7; H δ: 7.17–7.4 (m, 20H, arom); 3.5 (dd, J = 7.0, 4H,
CH2); 3.1–3.2 (m, 1H, NH). Mass spectrum (m/z): 460 (M+),
203 (48%), 201 (100%), 183 (48%).
P
1
To a solution of 3.3 g (0.055 mol) of 1,2-ethylenediamine,
15.3 ml of distilled triethylamine and 100 mg de 4-(dimethyla-
mine)pyridine in 50 ml of dry tetrahydrofuran were added
dropwise to a solution containing 10 ml (0.055 mol) of
chlorodiphenylphosphine in 100 ml of tetrahydrofuran. After
3 h of intense stirring, at room temperature, the solution was
filtered and the solid residue washed with tetrahydrofuran. The
filtrate was evaporated and the light brown oil was washed three
2.3. Ni complexes preparation
2.3.1. (N,Nꢀ-(Diphenylphosphoro)-
1,2-phenylenediamine)NiBr2 (I)
To a tetradydrofuran solution containing 0.71 mmol of N,Nꢀ-
(diphenylphosphine)-1,2-phenylenediamine was added to an
equimolar amount of C4H10O2NiBr2. The reaction was main-
tained under stirring for 4 h at room temperature. The solvent
was dried and the product was washed with pentane and dried
under vacuum, giving a pink powder. IR (KBr disk, cm−1) 911;
1100; 3210; 3327. Mass spectrum (m/z): 682 (M+), 508 (10%),
308 (20%), 290 (100%), 262 (20%), 201 (30%), 183 (58%).
2.3.2. (N,Nꢀ-(Diphenylphosphoro)-
1,2-ethylenediamine)NiBr2 (II)
To a tetradydrofuran solution containing 1.2 mmol of N,Nꢀ-
(diphenylphosphine)-1,2-ethylenediamine was added to an
Fig. 1. Reaction for the synthesis of the aminophosphine ligands.

M.C.B. Dolinsky et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 267–274
269
equimolar amount of C4H10O2NiBr2. The mixture was main-
tained under stirring for 4 h. The solvent was then removed under
vacuum, the solid product was washed with pentane and dried
and the solid obtained was dispersed in dried pentane. The
mixture was then submitted to ultrasound, generating a homo-
geneous suspension of catalyst to be used in the polymeriza-
tion.
under vacuum, giving a light green powder. IR (KBr disc, cm−1
)
744; 1101; 3333. Mass spectrum (m/z): 821 (M+), 792 (10%),
The polymerizations were performed in a 1000 ml dried and
¨
765 (70%), 737 (100%), 736 (78%), 262 (58%), 121 (58%).
argon flushed Buchi glass autoclave. The pentane suspension of
the catalyst was introduced into the reactor under slightly posi-
tive argon pressure and dried pentane was added until complete
500 ml. The reactor was kept at the desired temperature under
stirring and ethylene was introduced to the reactor vessel, initiat-
ing the polymerization. All the reactions were carried out under
pressure of 10 bar. After 1 h, the mixture was filtered under pres-
sure and the solid fraction was washed several times with a dilute
aqueous HCl solution in order to deactivate the catalyst system.
The polymer was finely washed with water and methanol and
dried under vacuum.
2.3.3. (N,Nꢀ-(Diphenylphosphoryl)-
1,2-phenylenediamine)NiBr2 (III)
To a tetradydrofuran solution containing 0.65 mmol of N,Nꢀ-
(diphenylphosphoryl)-1,2-phenylenediamine was added to an
equimolar amount of C4H10O2NiBr2. The mixture was main-
tained under stirring for 4 h. The solvent was then removed under
vacuum and the solid product was washed with pentane. After
drying under vacuum, a green powder was obtained. Mass spec-
trum (m/e): 959 (M+), 417 (10%), 308 (46%), 289 (100%), 213
(78%), 201 (38%), 183 (20%), 108 (100%).
The liquid fraction obtained from the separation of the poly-
merization mixture was distilled at 50 ◦C in order to separate
oligomers with higher boiling points from pentane. The remain-
ing liquid was analyzed by gas chromatography.
2.3.4. (N,Nꢀ-(Diphenylphosphoryl)-
1,2-ethylenediamine)NiBr2 (IV)
To a tetradydrofuran solution containing 0.65 mmol of
N,Nꢀ-(diphenylphosphoryl)-1,2-ethylenediamine was added a
equimolar amount of C4H10O2NiBr2. The mixture was main-
tained under stirring for 4 h. The solvent was then removed under
vacuum and the solid product was washed with pentane. After
drying under vacuum, a pink powder was obtained. IR (KBr disk,
cm−1) 749; 1180; 1125; 3327. Mass spectrum (m/z): 935 (M+),
859 (10%), 611 (22%), 385 (100%), 308 (10%), 262 (22%), 185
(40%).
2.5. Polymer characterization
13C NMR spectra were obtained on a Varian Mercury
300 FT-NMR spectrometer. Polymers were analyzed in 1,2,4-
trichlorobenzene (TCB)/benzene-d6 solution. Branching num-
berwasevaluatedaccordingtoliterature[21]. Molecularweights
of polymers were measured in TCB on a Waters plus 150CV plus
chromatograph at 135 ◦C. Monodisperse polystyrene standards
were used for calibration. Thermal analyses were performed on
a Perkin-Elmer DSC7 differential scanning calorimeter at heat-
ing rate of 10 ◦C/min. The degree of crystallinity was calculated
fromthemeltingenthalpy(293 J/gwasusedfor100%crystalline
polyethylene).
Fig. 2 shows the proposed structures of the complexes I–IV.
2.4. Polymerization
A solution of 10 mg of the Ni complex in 10 ml of dried
toluene was prepared and kept under stirring in argon atmo-
sphere. Methylaluminoxane (MAO) Witco purchased as a
10 wt% solution in toluene was then added to give the pre-
scribed Al/Ni ratio. The Ni complex/MAO solution was dried
3. Results and discussion
The complexes were tested as catalyst in ethylene poly-
merization using MAO as activator at temperature range from
−10 to 55 ◦C and Al/Ni ratio = 2000 (excepting entry 9). In all
cases the production of oligomers were detected. The influence
of temperature on polymer/oligomer production and polymer
microstructure was investigated. Table 1 shows the results of
polymerizations carried out in presence of the different Nickel
complexes (I–IV) at different temperatures.
3.1. Catalyst activity
The results of Table 1 indicated that the polymer/oligomer
production is highly dependent on the reaction temperature.
Considering the polymerization at 30 ◦C (entries 2, 6, 10 and
11), the aminophosphine complexes I and II showed the high-
est catalytic activity, in terms of ethylene consumption, when
compared to the aminophosphoryl complexes III and IV.
The influence of reaction temperature on polymer/oligomer
production showed a peculiar behavior. At lower temperatures,
the complexes showed highest activities, considering ethylene
Fig. 2. Proposed structures for the nickel-aminophosphine and aminophosphine
oxide complexes.

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M.C.B. Dolinsky et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 267–274
Table 1
Oligo/polymerization of ethylene with the nickel bis(aminophosphine)s and bis(aminophosphine oxides) complexes
a
b
c
Entry Complex Al/Ni ratio Reaction
temperature (◦C)
Catalytic activity
(g/mol Ni h bar)
Mn
Mw/Mn Tm (◦C) Tc (◦C) Xc (%) Branches Total ethylene
(%)
consumption (l)
1
2
3
4
I
2000
2000
55
30
5
−10
55
30
20809
3757
527500
7639
259100
–
3.2
19.4
6.9
–
124
125
127
–
111
112
112
–
7.7
9.0
28.0
–
6.13
7.89
4.21
–
18.0
83
15.0
12.6
2601
d
5
6
7
8
II
25268
2149
1612
1612
384100
36100
1455
4.7
4.7
1.3
1.7
126
123
118
122
112
112
107
109
14.5
10.3
1.9
3.20
–
1.8
2.43
4.0
5.5
16
5
−10
1360
20.6
60
9
10
III
IV
1000
2000
30
30
2189
1250
–
–
15.0
127
131
114
115
6.87
35.72
1.12
1.91
0.5
5.0
86900
11
2000
30
10156
35700
6.0
130
115
43.73
0.03
6.25
a
b
c
d
Tm: melting temperature.
Tc: crystallization temperature.
ꢀHm◦ = 293 J/g.
Only oligomers.
consumption, but as the temperature decreases the polymer pro-
ductivity was reduced. It means the complexes presented high
selectivity in forming, predominantly, oligomers at low tem-
perature. This behavior can be well exemplified in entries 5–8.
In general terms, the phosphine Nickel complexes (I and II)
showed an increase in catalytic activity related to polymer pro-
duction as temperature increases.
The mentioned behavior can be explained taking into consid-
eration the process of chain termination. At low temperatures,
the catalysts are probably more stable. However, it seems that at
these lower temperatures the occurrence of ␤-hydrogen elimina-
tion is increased, resulting in formation of oligomers. Thus, one
possible explanation could be that, at low temperature, molecu-
lar spinning of phenyl rings, which is one of the main sources of
steric hindrance around nickel in these complexes, are restricted.
This may increase the frequency of ␤-agoustic hydrogen inter-
action that is the main step for chain termination by ␤-hydrogen
elimination.
The more flexible aliphatic aminophosphine complex II
showed the highest catalytic activity at low temperature (entry
8). At temperatures below zero, octene and/or its isomers were
formedpredominantly. Theresultsobtainedmaybeexplainedby
the stability of phosphorus–nickel bond, once the 3-substituted
phosphine shows a strong bond with nickel, due to the donor
effect of the electron pair of phosphorus atom and the empty d
orbital of the metal ion. On the other hand, 5-substituted phos-
phorus acquires a very high stability after bonding to oxygen
(130 kcal/mol), once phosphorus has completed the eight elec-
trons around its nucleus. In this case, the metal–ligand bond
does not occur at the phosphorus atoms and only the oxygen or
nitrogen is able to bond to the metal. P–Ni bonds probably do
not allow rupture after addition of the cocatalyst. At the same
time, may generate active species with useful life time, once per-
mits the production of seven-membered ring, which contributes
to the complex stability. N–Ni bonds are theoretically less sta-
ble than P–Ni bonds but in this case it is possible to produce
five-membered ring which also contribute to the stability of the
complex. These preliminary polymerization results showed that
both catalysts (aminophosphines and aminophosphine oxides)
have satisfactory activity.
The effect of Al/Ni ratio on catalytic activity is considered
in entries 9 and 10 of Table 1. From the table, it is possible
to conclude that, in terms of total ethylene consumption, at
Al/Ni = 2000 higher catalytic activity was obtained, but higher
production of polyethylene was achieved at Al/Ni = 1000.
3.2. Polymer molecular weight
All the complexes produced polymers with high molecu-
lar weight and broad molecular weight distribution depending
on the polymerization condition. Polyethylenes formed by the
aminophosphine complexes I and II presented molecular weight
even higher than 200,000. While GPC analyses reveal that
the polymer obtained at 55 ◦C with I and II presented only
one peak (Fig. 3a), the polyethylenes produced at −10, 5 and
30 ◦C showed two or three peaks. Fig. 3b and c present typical
GPC curves of the polymers obtained with complexes II and
III at 30 ◦C, respectively. The polymers obtained at 30, 5 and
−10 ◦C are probably a mixture of polyethylenes of different
molecular weights from high oligomers to very high molecu-
lar weight polymers. The maximum of these peaks appear at
retention volumes equal to 20, 23 and 28 ml which corresponds
approximately to a molecular weights Mp = 106, 105 and 103,
respectively. The peak intensities were highly dependent on the
reaction temperature.
The multimodal molecular weight distribution showed by
the GPC curves indicates that there are at least three types of
active species performing ethylene polymerization in the men-
tioned conditions. In this case these polymerization sites con-
tribute for the simultaneous production of significantly different
polymers, broadening the polymer molecular weight distribu-
tion.
The increase in temperature from 30 to 55 ◦C probably deac-
tivate the less stable species, favoring the most stable one which

M.C.B. Dolinsky et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 267–274
271
Another hypothesis to be considered to explain both the mul-
timodal molecular weight distribution and the single peak at high
temperature is the occurrence of oligomer reinsertion during the
polymerization. Theenergyassociatedwitheachpolymerization
temperature may indicate this behavior, once the high temper-
ature could induce reinsertion of oligomers with double bond
end group, producing higher molecular weight polymers and a
monomodal GPC curve.
At 55 ◦C the catalysts produced molecular weight over
500,000 and at −10 ◦C mainly oligomers were produced.
Another hypothesis to explain this dramatic difference in the
molecular weight with temperature is based on the nature of
the ligands. At low temperatures phenyl ring rotation and/or
vibration of the bulky phosphine ligands around the nickel may
be considerably decreased, favoring ␤-agoustic interactions and
subsequentchainterminationby␤-hydrogenabstractionasillus-
trated in Fig. 4. On the other hand, at high temperatures increas-
ing rotation and vibration of the bulky phospine ligands may
occur, increasing steric hindrance and avoiding chain transfer
involving the chain ␤-hydrogen.
3.3. Polymer structure
According to 13C NMR and DSC analyses some of the
polyethylenes produced with these catalysts are considerable
branched, showing Tm in the range of 118–130 ◦C. The com-
plexes containing the oxidized ligand (III and IV) produced
more linear polyethylenes with Tm around 130 ◦C.
Fig. 3. GPC curves for the polyethylenes produced with nickel-aminophosphine
catalyst: (a) catalyst I at 55 ◦C and (b) catalyst II at 30 ◦C, and aminophosphine
oxide: (c) catalyst III at 30 ◦C.
produces single broad GPC peak. It is also possible that if the
species which generates low MW polymers are still active at this
temperature (55 ◦C) the differences of kinetics of each species
are small.
The branch content was evaluated by 13C NMR using the
methodology reported by Galland et al. [21]. Values of branch
percentage between 0.03 and 7.9% (Table 1) were obtained and
these polyethylenes can be considered as low branched polymers
Fig. 4. Proposed scheme for oligomer formation by ␤-hydrogen elimination and branching in addition-catalyzed reactions with aminophosphine complexes.

272
M.C.B. Dolinsky et al. / Journal of Molecular Catalysis A: Chemical 258 (2006) 267–274
Fig. 6. DSC traces of polyethylenes produced with: (a) aminophosphine com-
plex II at 55 ◦C and (b) aminophosphine oxide complex IV at 30 ◦C.
Polyethylenes with low degree of crystallinity (Xc) were
obtained, once the DSC analysis presented Xc results from 2 to
43%. The differences in Xc observed among the polyethylenes
produced from the four catalysts are probably due to the dif-
ferent and broad molecular weight distribution generated at the
different polymerization temperatures.
Fig. 5. 13C NMR of polyethylenes produced with: (a) aminophosphine complex
II at 55 ◦C and (b) aminophosphine oxide complex IV at 30 ◦C.
3.4. Oligomer analysis and characterization
(Fig. 5a and b). The branches affect the polymer properties such
as processability and crystallinity. For instance, long branches
increasethemeltflowindexandimprovepolymerprocessability,
while the increase in the content of short branches decreases the
polymer crystallinity and Tm.
The polymers produced with the aminophosphine com-
plexes I and II presented lower Tm (118–128 ◦C) than those
obtained with the aminophosphine oxide complexes III and IV
(130–131 ◦C). This indicates presence of higher branch con-
tent in the polymers produced by the aminophosphine catalysts.
The melt temperatures indicate that the polymers produced
with these nickel-aminophosphine catalysts showed a behavior
which is intermediate between LDPE (105–115 ◦C) and HDPE
(133–138 ◦C).
All the DSC traces showed broad peaks in the first heat-
ing, indicating the existence of broad distribution of crystal
sizes in the produced polymer. In the second heating, the peaks
became narrowest, but still broad. Typical DSC traces of these
polyethylenes showing the melting (second heating) and crys-
tallization peaks are presented in Fig. 6.
Polymerization experiments produced not only polymers but
also retrievable fractions of oligomers obtained after solvent
(pentane) distillation. For some catalysts tested and in spe-
cific experimental conditions, mainly oligomers were produced.
The distilled fractions were submitted to gas chromatography.
Table 2 presents the results of the analysis.
Oligomers with up to eight carbons, including the solvent
used in the polymerization were identified. The data were com-
pared to a standard sample of pentane:1-hexene:1-octene = 1:1:1
(volume). By comparison with the retention times of the stan-
dard sample, components of the standard as well as its isomers
were identified as reaction products.
Liquid oligomers recovered from the polymerizations at
55 ◦C showed a small fraction of octenes and a considerable per-
centage of oligomers with retention time between hexenes and
octenes (12–15%). These intermediate fractions were ascribed
to branched octenes, once the branches reduce the boiling point
of hydrocarbons.
For the catalyst II, the behavior at 30 ◦C was similar to that
observed at 55 ◦C. On the other hand, the catalyst I produced

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273
Table 2
Gas chromatography analysis of oligomers generated by the nickel catalysts
Complex
Reaction
temperature (◦C)
Gas chromatography (area%)
Hexenes
Fraction with tR
between C6 and C8b
Octenes
Solvents + higher molecular
weight fractions
I
55
30
5
−10
23.5
32.4
36.6
13
11.7
14.9
24.9
40.9
4.25
7.1
11.6
2.3
58.8
44.1
25.1
43
II
55
30
5
−10
18.9
22.9
45.1
44.3
14.7
11
9.3
8.7
4.3
17.5
24.09
55.4
59.7
28.5
20.6
6.95
III
30
30
30
28.0
10.46
44.3
10.0
13.4
11.0
0.4
2
61.2
74.0
22.2
IIIa
IV
22.3
a
Al/Ni = 1000.
tR: retention time.
b
higher octene fractions, although the intermediate C6–C8 frac-
tion was still considerable. At 5 ◦C both complexes showed
higher percent of octenes, but complex I showed a tendency
of producing the 2.7 min retention time (tR) product, identified
as a intermediate C6–C8.
Among the four catalysts used in this work, aminophosphine
catalysts present the highest activity, consuming up to 60 l/h
of the monomer at 10 bar. In general, these catalysts had simi-
lar behavior concerning polymers molecular weight distribution
with broad multimodal GPC curves at lower temperatures and
unimodal curves at 50 ◦C. The more flexible complex II con-
taining the aliphatic aminophosphine ligand showed the highest
catalytic activity. As polymerization temperature decreases, the
amount of oligomer generated increases while polyethylene
yield decreased. Low temperatures favors oligomer production,
mainly C6–C8.
At −10 ◦C, mainly fractions higher than hexenes were pro-
duced. The catalyst II generated several fractions with close
retention times, near the octene retention time, which may sug-
gest the production of 1-octence isomers. On the other hand, the
catalyst I produced preferentially a high intensity peak product
with retention time 2.7 min, already observed at 5 ◦C.
Catalysts I and II showed different behavior under the exper-
imental polymerization conditions. While catalyst I produced
mainly one product as the temperature decreased (tR = 2.7 min,
intermediate between C6 and C8), catalyst II produced several
peaks with close retention times, near the octene tR, which may
be octene isomers.
Catalysts III and IV produced considerable quantity of inter-
mediate C6–C8 fractions, however catalyst IV generated hex-
enes and octenes in high yields.
Catalysts I, II and IV showed potential to produce liquid
oligomers under specific conditions. This behavior is interest-
ing because liquid oligomers may be used as comonomers for
branched polyethylene production using the metallocene tech-
nology. In fact, reinsertion of these oligomers is one of the
possibility that cannot be neglected for explain the branched
nature of the polymers obtained in this work.
Acknowledgement
The authors thank the Brazilian Agencies CNPq-Conselho
´
´
Nacional de Desenvolvimento Cientıfico e Tecnologico
(Projects CNPq/PADCT, PRONEX 0327.00/00 and CTPetro)
and CAPES for partially support this work. The author also
thanks Prof. Helmut Alt and Bayreuth University for allowing
the possibility of performing part of the experiments presented
in this paper.
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