Propylene polymerization with nickel-diimine complexes containing pseudohalides
Descripción
Propylene Polymerization with Nickel–Diimine Complexes Containing Pseudohalides MARCOS L. DIAS,1 LUCIANA P. DA SILVA,1 GERALDO L. CROSSETTI,2 GRISELDA B. GALLAND,3 CARLOS A. L. FILGUEIRAS,4 CLA´UDIO M. ZIGLIO4 1 Instituto de Macromole´culas Professora Eloisa Mano, Universidade Federal do Rio de Janeiro, CP 68525, 21945-970, Rio de Janeiro, RJ, Brazil 2
Departamento de Quı´mica e Fı´sica, Universidade de Santa Cruz do Sul, Avenida Independeˆncia, 2293, 96815-900, Santa Cruz do Sul, RS, Brazil
3
Instituto de Quı´mica, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonc¸alves, 9500, 91.501-970, Porto Alegre, RS, Brazil
4
Departamento de Quı´mica Inorgaˆnica, Instituto de Quı´mica, Universidade Federal do Rio de Janeiro, CP 68563, 21.945-970, Rio de Janeiro, RJ, Brazil
Received 28 March 2005; accepted 16 July 2005 DOI: 10.1002/pola.21013 Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: DADNiX2 nickel–diimine complexes [DAD ¼ 2,6-iPr2 C6H3 N¼ ¼C(Me) C(Me)¼ ¼N 2,6-iPr2 C6H3] containing nonchelating pseudohalide ligands [X ¼ isothiocyanate (NCS) for complex 1 and isoselenocyanate (NCSe) for complex 2] were synthesized, and the propylene polymerization with these complexes and also with the Br ligand (X ¼ Br for complex 3) activated by methylaluminoxane (MAO) were investigated (systems 1, 2, and 3/MAO). The polypropylenes obtained with systems 1, 2, and 3 were amorphous polymers and had high molecular weights and narrow molecular weight distributions. Catalyst system 1 showed a relatively high activity even at a low Al/Ni ratio and reached the maximum activity at the molar ratio of Al/Ni ¼ 500, unlike system 3. Increases in the reaction temperature and propylene pressure favored an increase in the catalytic activity. The spectra of polypropylenes looked like those of propylene–ethylene copolymers containing syndiotactic propylene and ethylene sequences. At the same temperature and pressure, system 2 presented the highest number of proC 2005 Wiley Periodicals, Inc. pylene sequences, and system 3 presented the lowest. V J Polym Sci Part A: Polym Chem 44: 458–466, 2006
Keywords: addition polymerization; isoselenocyanate; isothiocyanate, nickel–diimine complexes; metal-organic catalyst/organometallic catalyst; poly(propylene) (PP); propylene polymerization; pseudohalide ligands
INTRODUCTION The synthesis of a-diimine complexes of nickel II for applications in olefin polymerization, espeCorrespondence to: M. L. Dias (E-mail: mldias@ima. ufrj.br) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 44, 458–466 (2006) C 2005 Wiley Periodicals, Inc. V
458
cially ethylene and propylene, has gained considerable attention.1–7 These complexes activated by methylaluminoxane (MAO) are capable of polymerizing ethylene, propylene, and other a-olefins into high-molecular-weight polymers with high activities. Dramatic differences in the microstructures of polymers made by these nickel-based catalysts have been observed in comparison with polymers made with early-transition-metal com-
PROPYLENE POLYMERIZATION
pounds used in Ziegler–Natta and metallocene technology.2 The properties of these polymers are highly dependent on the chelating diimine ligand of the nickel complex and reaction conditions and can be varied from rigid, semicrystalline polymer plastics to soft, amorphous elastomers.3,4 According to the accepted mechanism for polymerizations with these catalysts,2,3 the active site is formed by the abstraction of the nonchelating ligand with the formation of cationic species. With this assumption taken into consideration, the influence of the nonchelating ligand on the catalyst activity and polymer microstructure is not expected. Recently, we reported differences in the behavior of ethylene polymerization with some nickel–diimine complexes containing two different pseudohalides, isothiocyanate (NCS) and isoselenocyanate (NCSe), as nonchelating ligands.8 The observed differences were attributed to the formation of an ion pair containing these bulkier pseudohalide ligands in comparison with the common halide usually employed. There are few publications about the influence of nonchelating ligands and polymerization conditions on the catalyst activity and polymer features when nickel–diimine complexes are used in propylene polymerization.5–7,9,10 We have investigated propylene polymerization with nickel–diimine complexes containing the pseudohalides NCS (1) and NCSe (2) as nonchelating ligands (Fig. 1) to obtain information on the reaction behavior and polymer microstructure. In this article, we discuss the influence of these pseudohalides on the polymerization of propylene with MAO as a cocatalyst. The effects of the Al/Ni molar ratio, reaction temperature, and monomer pressure on the catalyst activity, average molecular weights, molecular weight distribution (MWD), and microstructure of the obtained polypropylene were studied. The results are discussed, and their performance is compared with that of the analogous bromide.
459
Figure 1. Nickel–diimine complexes used for the polymerization of propylene (X ¼ NCS for complex 1, NCSe for complex 2, and Br for complex 3).
Germany) was purchased as a 10 wt % solution in toluene. Nitrogen (White Martins, Brazil) and propylene (Polibrasil, Brazil) were treated ˚ ) and CuO columns. with a molecular sieve (3 A DADNiX2 nickel–diimine complexes 1 and 3 [DAD ¼ 2,6-iPr2C6H3 N¼ ¼C(Me)C(Me)¼ ¼NC6H3 2,6-iPr2; X ¼ NCS for complex 1 and NCSe for complex 2] were synthesized according to procedures previously reported.8,10 Complex 2 containing the pseudohalide NCSe as a nonchelating ligand was synthesized as described next. Synthesis of Bis(isoselenocyanate)N,N0 -bis(2, 6-diisopropylphenyl)-2,3-butanediimine Nickel {[ArN¼ ¼C(Me)C(Me)¼ ¼NAr]Ni(NCSe)2 or 2} Complex 2 was prepared by the reaction of 800 mg (1.6 mmol) of complex DADNiBr2 with 265.7 mg (1.06 mmol) of KNCSe, previously dried in vacuo at 120 8C, in 25 mL of MeCN. The solvent was maintained under reflux for 30 min until complete dissolution of the nickel halide and was refluxed for 6 h more. The solvent was removed in vacuo, and a violet solid was obtained (Scheme 1). ELEM. ANAL. Calcd.: C, 53.96%; H, 6.48%; N, 4.50%. Found: C, 53.47%; H, 6.46%; N, 4.52%. Polymerization
EXPERIMENTAL All the operations and manipulations were carried out under a dry nitrogen/argon atmosphere with Schlenk techniques. Materials Toluene was distilled with sodium and benzophenone under a nitrogen atmosphere. MAO (Witco,
Polymerization runs were carried out in a 250mL Parr stainless steel reactor. The reactor temperature was adjusted by a thermostatic bath. Toluene (100 mL), previously dried under sodium/benzophenone, was used as a solvent, and MAO was used as a cocatalyst in Al/Ni molar ratios in the range of 100–1500. The reactor was saturated with the gaseous monomer at a prescribed pressure. Polymerizations were performed at 1 and 3 bar of pressure of propylene at
460
DIAS ET AL.
Scheme 1. Synthesis of the nickel–diimine complexes (X ¼ NCS for complex 1, NCSe for complex 2, and Br for complex 3).
15, 25, and 50 8C for 1 h. For each experiment, 1.6 105 mol of Ni was suspended in toluene and transferred into the reactor under nitrogen. After 30 min of reaction, the polymerization was terminated by the transfer of the reaction mixture into an ethanol solution containing HCl. The solvent was removed, and the polymer was washed with water and dried in vacuo. Polymer Characterization The weight-average molecular weight (Mw) and MWDs were determined with a Waters 150 CV high-temperature gel permeation chromatography instrument equipped with a differential refractometer and three Phenomenex HT type columns (HT3, HT5, and HT6). 1,2,4-Trichlorobenzene was used as a solvent at a flow rate of 1 mL min1. The analyses were performed at 140 8C. The columns were calibrated with narrow-MWD polystyrene standards and then universally with linear low-density polyethylenes and polypropylenes. 13 C NMR was employed to determine the microstructure of the polypropylenes. The 13C NMR spectra were recorded at 90 8C with a Varian Inova 300 spectrometer operating at 75 MHz. Sample solutions of the polymers were prepared in ortho-dichlorobenzene and benzene-d6 (20% v/v) used to provide the internal lock signal. Spectra were taken with a 748 flip angle, an acquisition time of 1.5 s, and a delay of 4.0 s. The main assignments and calculations used to estimate the
sequence distributions were made according to previous literature.11
RESULTS AND DISCUSSION Influence of the Al/Ni Molar Ratio Table 1 shows the results of propylene polymerizations with the complex containing the NCS ligand activated by MAO (1/MAO) with different Al/Ni molar ratios. The changes in the catalytic activity, molecular weight, and MWD when the Al/Ni molar ratio was varied from 100 to 1500 are presented. The performance of this catalyst is compared with that of the analogous system 3/MAO. Comparing catalyst systems 1 (NCS) and 3 (Br), we can observe that the maximum activity was reached at Al/Ni molar ratios around 500 and 750, respectively (runs 1C and 1D and 3C and 3D), at which the activity reached 129.7 kg of PP mol of Ni1 h1 for catalyst 1 and 115.7 kg of PP mol of Ni1 h1 for catalyst 3. After this range of Al/Ni ratios, it slightly decreased. Complex 1 showed a relatively high activity even at a low Al/ Ni ratio. Polypropylenes obtained by these catalyst systems were high-molecular-weight polymers with Mw ranging from 230,000 (run 3D) to 315,000 g mol1 (run 1B). Small changes in Mw were observed with Al/Ni variation, suggesting that at high MAO contents in the polymerization medium, the effects of termination by chain transfer to aluminum were not important.
PROPYLENE POLYMERIZATION
461
Table 1. Influence of the Al/Ni Molar Ratio on the Catalyst Performance and Polymer Molecular Weight and Polydispersitya
Run 1A 1B 1C 1D 1E 1F 3A 3B 3C 3D 3E 3F
Catalytic Systems 1
3
Al/Ni
Yield (g)
Activity
100 200 500 750 1000 1500 100 200 500 750 1000 1500
1.178 0.957 2.075 1.505 1.977 1.752 — 0.092 0.934 2.011 1.686 1.852
73.6 59.8 129.7 94.1 123.6 109.5 — 5.7 58.4 115.7 105.4 115.8
b
Mw 104 (g mol1)
Mw/Mn
27.6 31.5 25.8 30.2 27.9 29.5 — 24.9 27.8 23.0 27.9 25.3
2.2 1.9 1.8 1.6 1.9 1.7 — 2.1 1.9 2.2 1.6 1.7
a Reaction conditions: propylene pressure ¼ 1 bar; [Ni] ¼ 1.6 105 mol/L; solvent: toluene (100 mL); reaction time ¼ 1 h; reaction temperature ¼ 258C. b Activity in kg PP (mol Ni1 h1).
The MWDs were narrow, with the weight-average molecular weight/number-average molecular weight (Mw/Mn) ratio around 2.0, suggesting single-site systems. No significant difference in the activity and molecular weight of polypropylenes was observed when the two compounds were compared (complexes 1 and 3), and this indicated that the polymerization was not markedly influenced by the exchange of Br for the pseudohalide NCS as a nonchelating ligand. Influence of the Reaction Temperature The influence of the reaction temperature on propylene polymerizations activated by MAO was
investigated. The results for the activity and properties of the materials obtained with catalyst systems 1, 2, and 3/MAO at 15, 25, and 50 8C and 1 bar of monomer pressure are presented in Table 2. When activated by MAO, complexes 1, 2, and 3 were active at all the temperatures tested. The three catalyst systems presented different stabilities according to the temperature used. For systems 1 and 3, an increase in the reaction temperature caused an increase in the catalyst activity. System 2 showed an opposite behavior, deactivating with increasing temperature. The complex containing NCS as a nonchelating ligand (1) was the most active at room temperature. At 15 8C, the system 2/MAO showed higher activity (130.5 kg
Table 2. Influence of Temperature on Polymerization of Propylene with Complexes 1, 2, and 3 Activated by MAO at 1 Bara Catalytic Systems 1
2
3
Run
T (8C)
Activityb
Mw 104 (g mol1)
Mw/Mn
1G 1C 1H 2A 2B 2C 3G 3C 3H
15 25 50 15 25 50 15 25 50
62.2 115.6 121.5 130.5 55.4 31.1 35.5 58.4 61.3
13.9 25.8 14.4 14.5 13.0 25.2 29.0 27.8 23.7
2.1 1.8 1.7 2.1 1.9 2.0 2.1 1.9 2.4
a Reaction conditions: propylene pressure ¼ 1 bar; Al/Ni ¼ 500; [Ni] ¼ 1.6 105 mol/L; solvent: toluene (100 mL); reaction time ¼ 1 h. b Activity in kg PP (mol Ni1 h1).
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DIAS ET AL.
Table 3. Catalytic Systems 1
2
3
Propylene Polymerization with Complexes 1, 2, and 3 at 3 Bara
Run 1I 1J 1K 2D 2E 2F 3I 3J 3K
T (8C)
Activityb
Mw 104 (g mol1)
Mw/Mn
15 25 50 15 25 50 15 25 50
78.6 205.5 16.2 16.4 42.8 36.5 81.4 108.8 89.9
— 35.5 28.0 29.5 34.1 35.4 31.9 33.8 21.9
— 2.3 1.9 2.4 2.2 2.3 2.0 2.4 3.0
a Reaction conditions: propylene pressure ¼ 3 bar; Al/Ni ¼ 500; [Ni] ¼ 1.6 105 mol/L; solvent: toluene (100 mL); reaction time ¼ 1 h. b Activity in kg PP (mol Ni1 h1).
of PP mol1 h1 in run 2A), and at 50 8C, the system 1/MAO presented higher activity (121.5 kg of PP mol1 h1 in run 1H). At all the temperatures studied, system 1 presented higher activities than system 3. Molecular weights from 130.000 g mol1 (run 2B) to 290.000 g mol1 (run 3G) were obtained. The MWD was narrow, with Mw/Mn ranging from 1.7 and 2.4. Regarding the effect of temperature on the molecular weight, it is interesting to note that the increase in the reaction temperature from 15 to 25 8C practically doubled the molecular weight of the polymer produced with 1/MAO. Nevertheless, at 50 8C, it was reduced to one-half of the molecular weight. On the other hand, for complex 3, the increase in temperature caused a decrease in the molecular weight, probably because of an increasing level of chain-transfer reactions that reduced the molecular weight. Influence of the Monomer Pressure The monomer pressure is an important condition for polymerization reactions with gaseous monomers and can strongly influence the polymer yield and microstructure. Table 3 presents the results of propylene polymerization at 3 bar and the three different temperatures used in this work. For complex 1, an increase in activity took place as the pressure was increased. Nevertheless, as the temperature was increased, the activity was raised from 15 to 25 8C but decreased from 25 to 50 8C. The catalyst system formed by complex 2 presented an abnormal behavior. For this complex, increasing the temperature favored an increase
in the activity from 15 to 25 8C. This behavior was different from that observed at 1 bar, at which a continuous decrease in activity occurred with increasing temperature. An increase in pressure from 1 to 3 bar, in general, caused a decrease in activity for this system. System 2 seemed to be much more influenced by both effects, pressure and temperature. For complexes 1 and 2, polymers with higher molecular weights were obtained when the pressure was raised from 1 to 3 bar. Complex 3 showed the lowest increase in Mw at the same range of pressure variation. Polymer Microstructure Influence of the Reaction Conditions on Monomer Insertion As already reported in the literature,12 nickel–diimine complexes produce PP with a considerable number of regioerrors. In the case of the three complexes used in this work, polypropylenes with a low amount of inversion and a very high percentage of sequence errors originating from 1,3insertions were generated. Table 4 presents results of a detailed 13C NMR analysis of the propylene polymers obtained with catalyst systems 1, 2, and 3. It shows the temperature and pressure effects on the microstructures of these polymers. Typical spectra of the propylene polymers obtained with these complexes are illustrated in Figure 2. All the obtained polymers looked like propylene–ethylene copolymers containing 35.2–43.6% PPP triad sequences and 10.1–16.0% of EEE triad sequences originating from 1,3-insertion. At
3 3 3 1 2 1 1 3
Run
3I 3J 3K 1J 2J 1I 1C 3C
15 25 50 25 25 15 25 25
Tp (8C)
3 3 3 3 3 3 1 1
Pp (bar) 40.1 40.2 35.2 41.6 43.6 42.7 36.7 41.9
[PPP] (%) 14.1 11.8 13.2 13.3 14.7 15.6 4.0 15.2
[PPE þ EPP] (%)
b
Calculated according to Ref. 12. A ¼ [(P)P*PP]. c B ¼ [(P*)P*PP]. d C ¼ 1,4-B1 bet E. e D ¼ 1,6-bcB1. f E ¼ long branch (n > 6).
a
B1 ¼ 1 carbon branch (methyl branch).
1,6-bcB1;
ethylene unit; 1,4-B1 between ethylene units;
propylene inverted unit;
propylene unit;
4.8 4.1 4.1 4.6 3.3 3.4 4.6 2.1
[EPE] (%)
A scheme for the definitions of microstructures is as follows:
Catalytic Systems 10.1 12.6 15.8 11.9 10.1 10.4 16.0 12.0
[EEE] (%) 17.1 16.4 13.4 14.5 15.9 14.9 11.5 17.1
[PEE þ EPP] (%)
Table 4. Microstructure of Propylene Polymersa Obtained with 1, 2, and 3/MAO
2.3 2.1 2.2 1.6 1.7 1.9 4.8 1.6
[PEP] (%) 1.1 0.8 0.1 0.6 0.6 1.2 0.9 0.4
[PP*P] (%) 1.3 1.3 2.9 1.0 1.5 1.5 4.9 1.2
[PPP*] (%) 0.9 0.5 0.3 1.2 0.6 0.9 1.2 0.4
Ab (%) 0.5 0.4 1.1 0.7 0.2 0.3 1.2 0.3
Bc (%) 1.6 1.1 0.9 1.2 0.9 1.2 0.7 0.6
Cd (%) 6.0 7.2 7.6 6.6 6.3 6.1 8.0 6.9
De (%)
0.2 0.2 1.3 0.6 0.4 0.0 0.4 0.3
Ef (%)
0.0 1.3 1.1 0.6 0.1 0.0 5.0 0.0
i-Bu (%)
0.1 0.0 0.7 0.1 0.2 0.1 0.2 0.1
2MH (%)
PROPYLENE POLYMERIZATION
463
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DIAS ET AL.
Figure 2. 13C NMR spectra for propylene polymers obtained at 25 8C with (a) 1/MAO (run 1J), (b) 2/MAO (run 2J), and (c) 3/MAO (run 3J).
the same polymerization temperature, complex 2 produced propylene polymers with the highest concentration of PPP triads (43.6%), followed by 1 (41.2%) and 3 (40.6%). Comparing the temperature effect for the same catalytic system, we can see for catalytic system 3 that when the temperature increased from 15 to 50 8C (runs 3I, 3J, and 3K), the [PPP] sequence decreased (from 40.1 to 35.2%) and the [EEE] sequence increased (from 10.1 to 15.8%). There was also an increase in long i-butyl and 2-methylhexyl branches and head-to-head (PPP*) and tailto-tail (P*P*PP) inversions and a decrease of one unit inversion (PP*P). This means that a temperature increase favored 1,3-enchainments, branching, and inversions of types A1 and A2.11 The effect of the temperature was also compared for system 1 from 15 (1I) to 25 8C (1J) at 3 bar. An increase in the temperature slightly decreased [PPP] triads (from 42.7 to 41.6%) and increased [EEE] triads (from 10.4 to 11.9%) and one-1,3enchainment (from 6.1 to 6.6%). Branching was also slightly favored by a temperature increase. Inversion was not very much affected by this increase in the temperature. The temperature effect was studied for system 1 from 15 to 25 8C at 3 bar. A temperature increase slightly decreased [PPP] triads and increased [EEE] triads and one-1,3-enchainment. Branching was also slightly favored by a temperature increase. Inversion was not very much affected by this. Comparing systems 1, 2, and 3 at the same temperature (25 8C) and pressure (3 bar), we can
see that system 2 (2J) gave the highest concentration of [PPP] sequences (43.6%) and catalyst 3 (3J) gave the lowest (40.2%). The system with the highest amount of 1,3-enchainment was system 3, and 2 had the lowest. System 1 presented a slightly higher number of inversions than the other two. Branching was very low in the three systems. In all cases, the polymers were formed by about 40 mol % [PPP] syndiotactic triads, a high number of EP sequences, and some branching and inversion. The pressure effect can be compared for catalyst 1 at 25 8C. An increase in pressure from 1 (1C) to 3 bar (1J) increased [PPP] sequences (from 36.7 to 41.6%) and decreased [EEE] sequences (from 16.0 to 11.9%). This suggests that one-1,3enchainment was less favored at higher pressures. Long branches and 2-methylhexyl branches were not much affected by pressure, but catalyst 1 showed an exceptional number of i-butyl branches at 1 bar. Inversion, in general, decreased with the pressure increase. Catalyst 3 presented very close values of [PPP] and [EEE] sequences, inversion, and branching at the two pressure studied (see runs 3C and 3J); therefore, it was not much affected by pressure. Influence of the Reaction Conditions on Polypropylene Tacticity The influence of the polymerization conditions on the tacticity of the propylene polymers obtained with complexes 1, 2, and 3/MAO is summarized in Table 5. The polymers obtained with the three
PROPYLENE POLYMERIZATION
Table 5.
Tacticity of Propylene Polymersa Obtained with 1, 2, and 3/MAO
Run
Catalytic Systems
T (8C)
PP (bar)
mm (%)
mr (%)
rr (%)
m (%)
r (%)
3I 3J 3K 1J 2J 1I 1C 3C
3 3 3 1 2 1 1 3
15 25 50 25 25 15 25 25
3 3 3 3 3 3 1 1
3.7 3.5 13.5 6.5 4.9 6.1 2.4 5.8
15.3 21.4 25.1 22.2 18.8 17.9 32.2 18.7
80.9 75.1 61.5 71.4 76.3 76.0 62.5 75.5
11.4 14.2 26.0 17.5 14.3 15.1 20.0 15.1
88.6 85.8 74.0 82.5 85.7 84.9 80.0 84.9
a
465
Determined according to ref. 12.
complexes were predominantly syndiotactic, with the concentration of rr syndiotactic triads ranging from 61.5 to 80.9%, presenting in some cases up to 88% r dyads. Complex 3 containing a bromide nonchelating ligand showed the highest syndiospecificity (80.9% rr) and was followed by complexes 2 (76.3% rr) and 1 (76.0% rr; runs 3I, 2J, and 1J). The methyl region of the 13C NMR spectra of polypropylenes obtained with catalysts 1 and 2 is presented in Figure 3. The effect of the monomer pressure on the tacticity is shown in runs 1C, 1J, 3C, and 3J. The opposite behavior was observed for complexes 1 and 3. Although rr triads decreased when the pressure was increased for PP obtained from 1, raising the pressure from 1 to 3 bar increased rr triads in PP obtained from 3. Relatively high syndiotacticity was obtained even at temperatures above 15 8C. The tacticity
was greatly affected by an increase in the temperature. For catalyst system 3, a temperature increase from 15 to 50 8C (3I, 3J and 3K) lowered rr triads from 80.9 to 61.5, increasing isotactic triads (mm) from 3.7 to 13.5. For catalyst 1, a temperature increase from 15 to 25 8C decreased syndiotacticity from 76.0 to 71.4 and increased isotactic triad formation from 6.1 to 6.5. At the same temperature (25 8C) and pressure (3 bar), catalyst 2 was the most syndiotactic (76.3 rr), and catalyst 1 was the least syndiotactic (71.4 rr). The pressure effect on tacticity was not so dramatic as the temperature effect. Catalyst 1 increased syndiotacticity (rr) from 62.5 to 71.4 when the reaction pressure changed from 1 to 3 bar. For catalyst 3, the pressure effect was inverted, and an increase from 1 to 3 bar in pressure increased rr triads from 75.1 to 75.5.
Figure 3. Methyl region of 13C NMR spectra for polypropylenes obtained (a) with 1/MAO at 25 8C, (b) with 1/MAO at 50 8C, and (c) with 2/MAO at 25 8C.
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DIAS ET AL.
CONCLUSIONS New DADNiX2 nickel–diimine complexes containing nonchelating pseudohalide ligands (X ¼ NCS for complex 1 and NCSe for complex 2) formed very active catalysts for the polymerization of propylene when activated by MAO. As the bromide analogues, these catalyst systems produced high-molecular-weight amorphous propylene polymers with structures similar to those of propylene–ethylene copolymers containing moderately syndiotactic propylene sequences and ethylene sequences. Complex 1 had higher activity than the corresponding bromide analogues. It showed relatively high activity even at low Al/Ni ratios. At the same temperature and pressure, system 2 presented the highest number of syndiotactic propylene sequences, and system 3 presented the lowest. This complex was the most sensitive to an increase in the polymerization temperature, drastically deactivating at temperatures above 50 8C.
The authors thank the Brazilian agencies Conselho Nacional de Desenvolvimento Cientı´fico e Technolo´gico (CNPq) [projects: Programa de Apoio ao Desenvolvimento Cientı´fico e Tecnolo´gico (PADCT), Programa de Apoio a Nu´cleos de Exceleˆncia (PRONEX), and Fundo Setorial de Petro´leo e Ga´s Natural (CTPetro)], Fundac¸a˜o Universita´ria Jose´ Bonifa´cio (FUJB), Fundac¸a˜o de Amparo a` Pesquisa do
Estado do Rio de Janeiro (FAPERJ), Fundac¸a˜o de Amparo a` Pesquisa do Estado do Rio Grande do Sul (FAPERGS), and Polibrasil for their partial support of this work.
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