Metal complex bicenter catalysts for olefin and diene polymerization

APPLIED CATALYSIS A: GENERAL ELSEVIER

Applied Catalysis A: General 166 (1998) 153-161

Metal complex bicenter catalysts for olefin and diene polymerization E. Mushinaa,*, I. Gavrilenko”,

E. Antipov”, Yu. Podolsky”, V. Frolova, E. Tinyakova”, B. Krentsela, M. Gabutdinovb, S. Solodjankinb, A. Vakhbreitb, C. Medvedevab, V. Cherevinb

a A. V Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 29 Leninsky pr, 117912 Moscow, Russia ’ “Kazanorgsintez” Stock Company, I Belomorskaya, 420051 Kazan, Russia

Received 24 January 1997; received in revised form 28 July 1997; accepted 30 July 1997

Abstract New bicenter metal-complex catalysts supported on dehydrated microspheric silica gel have been synthesized and tested in the polymerization of ethene and butadiene. The catalysts contain two components: a titanium-magnesiumor chromiumcontaining compound and an oligodienyl metal-aluminium complexes with a bridge structure (metal - Zr or Ni). A possibility of preparation of linear medium-density polyethylene by polymerization of ethene in gas-phase process without using comonomers was established. These catalysts also display high efficiency in the polymerization of butadiene, the products obtained being the mixtures of cis- and truns-polymers. It was found that titanium-magnesium catalysts modified by c 1998 zirconium+rganoaluminum compounds are most active in both ethene and butadiene polymerization processes. Elsevier Science B.V. Keywords:

Bicenter catalyst; Metal-aluminum

oligodienyl

complex; Linear polyethylene;

1. Introduction

In this article, bicenter (binuclear) metal-complex catalysts for polymerization of unsaturated compounds has been considered. These catalysts are composed of two metal-complex compounds. They are used in both homogeneous and heterogeneous catalyses and are mainly described in patent literature. It was shown that it is possible to prepare linear lowand medium-density polyethylene by polymerization *Corresponding 2302224.

author.

Tel.: +7 095 9554176;

fax: +7 095

0926-860x/98/$19.00 0 1998 Elsevier Science B.V. All rights reserved. PII SO926-860X(97)00250-0

Polybutadiene;

Microstructure

of ethene without use of co-monomers [ 11. Oligomerization of ethene and its copolymerization with the monomers produced during the process occur simultaneously. Homogeneous or supported compounds of titanium (or vanadium) [l-S] or chromium [9-l 31 are used as polymerizing agents, whereas Ti(OR)4 [l-3], (CsHs)sCr [4], (CHC00)2Ni [6], chelates of nickel, cobalt and iron [7] and ilide complexes of nickel [8] are used as oligomerizing agents (Table 1). It has been shown recently that bicenter catalysts show stereoregulating effect in polymerization of propene and 4methyl-1-pentene [ 141. The isotacticity of polypropylene prepared using titanium-magnesium catalyst

154 Table 1 Bifunctional

E. Mushina et nl./Applird

(binuclear)

1st Component

catalysts

of catalyst

Catalysis A: General 166 (1998) 153-161

for ethene polymerization

(copolymerization)

2nd Component

of catalyst

(oligomerization)

Reference

TiCL, (or VCL,) + AOC * TiC13/AlC13 + AOC a TiC14A4gC12 + AOC a

Ti(OR)I

[l-3]

n-(C3H&Cr lT-(C&)NiBrl2 (CH#.200)2Ni chelates of Ni, Co, Fe ilid complex of Ni

[41 I51 [61 171 WI

CrOz/SiOz Cp@Si02

ilid complex of Ni

[91

(7i-C3HsN& CrO+ NiO/Si02 (Ti02/Si02) + CO + Al(Alk)3 h Crj (TMSM)8 ’

[1()1 [Ill [I21 [131

” AOC - organoaluminum compound h Alk - i-C4Hs or C2HS. ’ TMSM - trimethylsilylmethyl.

modified

by tetrabenzylzirconium

achieves

98 wt%

[151. This paper reports new approaches to the synthesis of bicenter metal-complex catalytic systems deposited on dehydrated microspheric silica gel. The method for preparing the catalysts of this type includes the sequential precipitation of a titanium- or chromiumcontaining compound and oligodienyl metal-aluminum complexes (metal - nickel or zirconium) on the surface of dehydrated microspheric silica gel as the first and the second component, respectively. The paper describes the use of these catalysts in olefin and diene polymerization and some data on the effect of catalyst composition and conditions of polymerization on the structure and properties of the resulting polymers (polyethylene and polybutadiene), the data on polymerization of dienes on these catalysts being presented for the first time.

2. Experimental Monomers (ethene and butadiene) and solvents (pentane, isopentane, heptane, benzene, and toluene) were purified according to techniques conventional to the synthesis of co-ordination systems. Oligodienyl metal-aluminum complexes (metal nickel or zirconium), titanium-magnesium catalysts and bicenter catalysts were synthesized in an atmosphere of pure argon.

Bicenter (binuclear) catalysts were prepared by co-precipitation of titanium-magnesium or chromiumcontaining compounds and oligodienyl metalaluminum complexes on dehydrated microspheric silica gel. Titanium-magnesium catalyst supported on silica gel was prepared by mixing dehydrated microspheric silica gel with a titanium-magnesium catalyst (TMC) in pentane [ 161. In turn, TMC was prepared by reacting TiCL4 with anhydrous MgCla which was prepared by decomposition of butylmagnesium chloride with excess butyl chloride according to [17]. As a chromium-containing catalyst triphenylsilylchromate ( [(C6Hs)3Si0]2Cr0JSi02), supported on silica gel and treated with diethylaluminum ethoxide A1(OC2H5)(C2H& was used. The second component of bicenter catalyst-oligodienyl nicklealuminum (or zirconiumaluminum) complexes were prepared by reacting chloride of corresponding metal with triisobutylaluminum in the presence of diene (butadiene, isoprene, allene) in aromatic (benzene, toluene) or aliphatic (pentane, isopentane, heptane) hydrocarbon at 3040°C at a molar ratio of components as follows: metal/aluminumldiene = l/3/6 [ 181. Polymerization of ethene was mainly performed in the gaseous phase using two reactors. The first reactor was 1.5 1 autoclave equipped with a magnetic stirrer. The second reactor was 0.5 1 flow-type apparatus. Both reactors were equipped with a thermostat and

E. Mushina et al/Applied

155

Catalysis A: General 166 (1998) 153-161

a special unit for opening the ampules with a catalyst without contact with air. Pressure in the reactors was maintained constant by means of a contact manometer connected with a solenoid valve. Before the beginning of the experiment, the reactors were purged with pure ethene at 90°C for 2 h and the polymerization carried out for 15-20 min at a pressure of ethene of 0.20.5 MPa at 60-70°C. After prepolymerization was complete, the pressure of ethene was raised to 1.5 2.0 MPa and, then, polymerization was conducted at this pressure for 1 h. The microstructure of polyethylene prepared with bicenter catalysts was determined by IR spectroscopic analysis with a Bruker IFS- 133V instrument using the films of polyethylene with thicknesses of ca. lo30 pm. Molecular mass characteristics of polyethylene were determined with a Waters gel-chromatograph using columns packed with a macroporous glass and a Devison silica gel. o-Dichlorobenzene was used as eluent. The rate of elution was 1 ml/min. Physico-mechanical properties of polyethylene were studied using a TIRA-2200 tensile-testing machine at room temperature with a strain rate of 20 mm/min. The films used for physico-mechanical studies were prepared by pressing PE powder at 140°C at a pressure of 0.1 MPa. The films were kept at this pressure for 10 min, cooled in a water-ice mixture and the bands of 2 mm-width were cut. In the experiments, when tensile strength of the films was determined, the working length of the film was 20 mm. The ends of the bands, which were fixed in the clamps of the tensiletesting machine, were strengthened by stretching on iron at a temperature ca. 100°C. The density of polyethylene was determined by the flotation method. Polymerization of butadiene was conducted in glass ampules or dilatometers. After polymerization was complete, the polymer was precipitated from a solution with methanol containing an antioxidant (ionol) and dried under vacuum. Thermodynamic characteristics of polybutadiene were studied by the differential scanning calorimeter using a Mettler TA 4000 calorimeter. The sample of polybutadiene was heated from -60 to +2OO”C at a rate of 10 K/min. The microstructure of polydienes was determined by IR spectroscopy using a Specord M 82 instrument.

Composition and structure of oligodineyl metalaluminum complexes were studied by IR spectroscopic analysis of heptane solutions and from the data of chromatographic and mass spectral analyses of the decomposition products of these compounds. Analyses were performed with a chromatograph equipped with a glass capillary columns, using SE-30 as a stationary phase, and an LKB-2091 mass spectrometer (capillary column 80 n-JO.25 mm, Apieson L as a stationary phase, 70 eV) in the 60-l 20°C range. Components of the catalyst were analyzed for the content of metals (Ti, Ni, Zr, Al).

3. Results and discussion 3.1. Bicenter metal-complex

catalysts

As already mentioned, the oligodienyl complexes were obtained by the exchange reaction between chloride of transition metal and (i-C4H9)3A1 in the presence of diene: MCI, + (&CqHg)3AI + (i-CqHg) MCI,., + (I-C,H~)~AICI 1 i-C4H8 + HMCI,.,

n(CrHd/ WWdnMCI,.,

\W,Hd WC~Hd,,MCI,,-,

where: M = Ni or Zr; m = 2 or 4; n = 2-7

According to the scheme the decomposition of (i-C4H9) MCl,_1 takes place and the elimination of i-CdHs was confirmed chromatographically. The structure and composition of the complexes obtained were studied by chromate-mass spectrometry and IR spectroscopy. To determine the composition of oligomers of isoprene, oligodienyl complex of zirconium was decomposed with hydrochloric acid and the reaction products were analyzed gas chromatographically and mass spectrometrically. In the decomposition only products, the hydrocarbons of type [(CsH& + 2H] (n = 2 + 7) were found. The absence in these of butyl radicals allows the suggestion to be made that the insertion of the first molecule of the diene takes place at the M-H but not M-C bond. The data of analysis of decomposition products are summarized in Table 2. As can be seen, composition

156

E. Mushina et al./Applied

Table 2 Dependence mol)

of composition

Concentration of Zr in solution! (mol/l)

0.062 0.058 0.030 0.020

of oligodienyl

Catalysis A: General 166 (1998) 153-161

ligands on conditions

Al/Zr (mol/mol)

6 3 3 3

of synthesis of zirconium-aluminum

Content of monomer

units in ligands (wt%) (n

organic compound.

number of monomer

(CsHs/Zr = 6 mol/

units)

n=2

n=3

It=4

n=S

n=6

n=7

38 20 20 20

21 21 28 25

19 25 22 27

12 12 11 15

6 9 11 8

4 I 8 5

C4H9)2AlCl, which contain bond, 300 cm-‘):

60

CH,

bridge structure

C I-- Zr ’

(Zr-CL

‘Al(i-C4H9)2

’ ‘\J ‘\ Cl \

a 1600

1400

1200

1030

Freuuencv. Fig. 1. IR-spectrum

SW

600

400

200

cm-’

of zirconium-aluminum

organic compound

of oligomers of isoprene almost does not depend on the concentration of zirconium in solution during the synthesis of oligodienyl metal-aluminum complex. An increase in the Al/Zr molar ratio leads to an increase in the amount of dimers. In addition, these data show that oligomerization of isoprene is accompanied by predominant formation of di-, tri, and tetramers. In the IR spectrum of oligodienyl zirconium-aluminum complex (Fig. I), the band at 530 cm-’ corresponding to the Zr-CL bond in ZrCL4 decreases in intensity and shifts to 545 cm-‘. At the same time, the new bands emerge at 495 and 435 cm-‘. The emergence of these two bands can be attributed to the forming of Zr-C bonds. 7r-Alkenyl structure is characterised by the bands at 545, 1015, 1280, and 15001570 cm-‘, all these bands disappearing upon contact of the complex with air. It was also shown that the oligodienyl compounds form complexes with (i-

The resulting oligoalkylidene (when allene is used) or oligodienyl (in the case of isoprene or butadiene) ligands stabilize metal-organoaluminum complexes due to formation of 7r-complexes between the metal and oligodienyl ligands [ 191. In the case of titanium-magnesium supported catalyst, reaction of oligodienyl metal-aluminum complexes can proceed either with free hydroxyl groups of silica gel or with titanium-magnesium component anchored on silica gel (hypothetical scheme in Fig. 2). Simultaneous fixation of two metal-complex

_,-_,_t I’ I /c’\ MgCl

,

CL

_,i_,-:y

dl ’ CI ’

&I ’ CI ’ c1

-.5,-o-

Al

/

’ Mgcl

*

a* Al

/

a

\I

CI zr-h--R

‘Cl ’dl

Cl

\I

zr-_Z--R

--Si-0-H

R’ ‘a’b

Fig. 2. The probable scheme of interaction between the oligodienyl zirconium-aluminum organic compound and surface of silica gel (L - CSHs; R - i-C4H9).

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157

Catalysis A: General 166 (1998) 153-161

Table 3 Activity of commercial chromium-containing catalyst modified oligodienyl zirconium and nickel compounds and physico-mechanical properties of formed polyethylene. Concentration of Cr in catalyst - 0.23 wt%; pressure 2 MPa; temperature 20°C; concentration of Hz in gas phase - 4 ~01% Ratio (mol/mol)

Activity (kg PE/g Cr/h)

Zr/Cr Zr/Cr Zr/Cr Zr/Cr Zr/Cr Ni/Cr Ni/Cr NiKr

14 24 23 30 24 29 11 9

a MI bo ’E dE -

= = = = = = = =

0.2 0.6 0.8 1.0 1.5 0.2 0.6 1.0

- melt index, g per 10 min. Measurement tensile strength. relative elongation at break. modulus of elasticity.

compounds accounts

on silica

gel

according

Physico-mechanical

properties

of PE

MIa

0 b(MPa)

&‘(8)

E d (MPa)

0.2 0.1 0.9 0.3 0.6 0.3 0.4 0.8

25 32 30 26 27 30 30 22

630 730 890 720 760 700 750 750

550 520 550 580 610 480 520 440

at 5 kg

to the

scheme

for their mutual effect and specificity of their

action. 3.2. Polymerization of ethene using bicenter metal-complex catalysts The prepared catalytic systems were used to produce medium density polyethylene by gas-phase polymerization of ethene without addition of comonomers. It turned out that the oligomers of ethene (1-butene, I-hexene, etc.) formed in situ under the action of oligodienyl complexes co-polymerize with ethene in the presence of titanium-magnesium or chromium-containing component. Bifunctionality of these catalytic systems was confirmed by chromatographic analysis of the reaction gas and by the data on microstructure of the resulting polyethylene. In the study of bicenter chromium-containing catalysts, polymerization of ethene was performed at 90°C using a laboratory flow-type setup. In these experiments, concentration of hydrogen was in the 2.5-4.0 ~01% range. Several series of the catalysts, which differ in the content of the modifying agent (molar ratio Ni/Cr and Zr/Cr varying in the 0.2-1.0 and 0.2-l 5 ranges, respectively), were synthesized and studied. The data of Table 3 show that when the Ni/Cr ratio grows the melt index increases and activity of the

catalyst concurrently drops. At the same time, elasticity of the polymer estimated as relative elongation at break remains unchanged at the level of 600-800%. Catalytic systems containing zirconium compound were more active under the same conditions (Table 3). The increased activity was observed in a wide range of ZrKr ratio, from 0.6 to 1.5. The melt index changes in the 0.3-0.9 range as the Zr/Cr ratio changes from 0.8 to 1.5. The samples of polyethylene prepared using chromium-containing catalyst modified by organozirconium compound show enhanced elasticity. According to the IR spectra, the tendency to increase in the degree of branching of macromolecules appears as the Ni/Cr or Zr/Cr ratio grows (Table 4). Polymerization of ethene with titanium-magnesium catalyst modified by organonickel or organozir-

Table 4 Structure of PE prepared with chromium-containing catalyst modified by oligodienyl zirconium and nickel compounds (according to IR-spectroscopy) Metal rat io (moVmo1)

-CHs-branching per 1000 atoms of C

Zr/Cr ZrlCr Ni/Cr NiKr

1.8 3.8 0.5 1.7

= = = =

0.8 1.6 0.2 1.0

Unsaturation per 1000 atoms of C trans-CH=CH-

-CH=CH?

0.19 0.17 0.03 0.10

0.52 0.65 0.27 0.28

158

E. Mushina et al./Applied

Catalysis A: General 166 (1998) 153-161

IOO-

3 . . ._ r?

.

80-

2

5

. 60G E b

.

.

?? a

&40“0 r

1

O-1

0

.

.

I

I

I

20

40

60

Time,

min

Fig. 3. The kinetics of polymerization of ethylene with (1) titanium-magnesium supported catalyst, and with the same catalyst modified by (2) nickel-aluminum organic and (3) zirconiumaluminum organic compounds. Pressure 1.5 MPa, temperature 9o”C, concentration of Ti in catalyst 0.5 wt%, Zr/Ti = 0.5 mol/ mol, Ni/Ti = 0.5 mohmol, and Al/Ti = 100 mol/mol.

conium compounds was carried out in the autoclave at 90°C at a pressure of 1.5 MPa. Fig. 3 shows the kinetic curves of the ethene polymerization with supported titanium-magnesium catalysts and with the same

catalysts modified by oligodienyl nickel and zirconium compounds. As is seen, titanium-magnesium catalysts modified by organozirconium compounds are the most active. Modification of the starting catalyst can raise the initial rate of polymerization almost by three times. Like chromium-containing catalysts, these systems are bifunctional catalysts, which cause oligomerization of ethene (derivatives of nickel or zirconium) and its copolymerization with the forming oligomers (titanium compounds). Table 5 presents the data on physico-chemical properties of PE prepared with titanium-magnesium catalysts of various compositions and on the activity of these systems. As is seen, the use of modified titanium-magnesium catalyst allows preparation of PE showing reasonable strength and relative elongation. These data indicate also that the modified titanium-magnesium catalysts are markedly more active in polymerization of ethene to the chromium-containing catalyst (see Table 3), with titanium-magnesium catalysts modified by organcompounds the highest ozirconium showing activity. Table 6 presents the data on the structure of polyethylene prepared with these catalysts. These data show that as the molar ratio of oligomerizing and polymerizing components of the catalyst increases the degree of branching grows. At the same time, the PE density decreases and varies in the 0.940-0.945 g/cm3 range.

Table 5 Activity of titanium-magnesium catalysts modified by oligodienyl zirconium and nickel compounds polyethylene. Al/Ti molar ratio 100 mol/mol; concentration of Hz in gas phase - 30 ~01% [Ti]/ (wt%)

0.25 0.25 0.25 0.50 0.50 0.50 0.50 0.50

Metal ratio (mol/mol)

Zr/Ti ZriTi Zr/Ti Zr/Ti Zr/Ti Zr/Ti NiiTi Ni/Ti

= = = = = = = =

0.5 1.O

1.5 0.2 0.5 1.0 0.5 1.0

a 0 - tensile strength. b E - relative elongation at break ’ E - modulus of elasticity.

Activity (kg PE/g Ti/h)

116 81 91 70 67 83 79 23

Physico-mechanical

and physico-mechanical

properties

properties

of

of PE

0 a (MPa)

Eb(%)

E ’ (MPa)

33 34 32 31 36 31 36 25

780 670 760 700 760 660 730 700

520 490 400 550 610 540 500 490

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Catalysis A: General 166 (1998) 153-161

159

Table 6 Structure of PE prepared with titanium-magnesium catalyst modified by oligodienyl zirconium and nickel compounds (according to IR spectroscopy). Concentration of Ti 0.5 wt% per SiOz Metal ratio (mol/mol)

-CHs-branching per 1000 atoms of C

Zr/Ti ZrITi ZrfTi Ni/Ti

1.1 I .4 5.9 1.2

= = = =

0.5 1.0 2.0 0.5

Unsaturation per 1000 atoms of C rrans-CH=CH-

-CH=CHa

0.14 0.07 0.18 0.12

0.08 0.26 0.03

Fig. 4 shows the dependences of the melt index on the molar ratio of modified metal to titanium, other being equal (Al/Ti ratio = 100, concentration of hydrogen 30 ~01%). When nickel is used as a modifying agent, the melt index increases almost by two times (to 2 g/l 0 min) as the Ni/Ti molar ratio increases from 0.5 to 1S. A change in the Zr/Ti molar ratio from unity to 1.5 does not have any effect on the melt index of the polymer. Table 7 summarizes the experimental data on molecular mass distribution of PE samples prepared with various catalysts. As is seen, the nature of the catalysts shows a significant effect both on the molecular mass of the polymer and on the pattern of molecular mass Table 7 Molecular Catalytic

mass characteristics system

Cr + Ni

Cr + Zr Ti/Mg + Ni

Ti/Mg + Zr

of PE prepared

Concentration

[Cr] 0.23 0.23 [Cr] 0.23 [Ti] 0.50 0.50 [Ti] 0.50 0.25 0.50 0.25 0.50 0.25 0.50

= 0.23

= 0.23 = 0.50

= 0.25

(wt%)

with the catalysts Ratio (mol/mol)

Ni/Cr 0.60 1.oo ZrKr 0.50 Ni/Ti 0.50 0.50 Zr/Ti 0.50 1.50 1.50 0.50 0.50 1.50 1.50

= 0.20

= .25 = 0.50

= 0.50

0.5 I 0.0

I 0.5

I 1.0

I 1.5

Ratio NijTi and Zr/Ti, mol/mol Fig. 4. Melt index (measured at 5 kg) vs. ratio of metals in Ti/Mg catalyst modified by (1) zirconium-aluminum organic and (2) nickel-aluminum organic compounds.

distribution. Polymerization of ethene using modified chromium-containing catalyst leads to the formation of polymer with very broad molecular mass distribu-

of different compositons

[Hz1(~01%)

3.5 3.5 3.6 3.6 3.5 5 30 30 5 5 5 5 30 30 30 30

Molecular

MwJM,

weight

M”

NV

15000 18800 15900 19 100 17 100 61000 57 000 45 000 159 000 150000 139 000 115000 52 000 47 000 57 000 60 000

280000 380000 382 000 375 000 422 000 435 000 373 000 240 000 663 000 519000 564 000 520 000 317000 291000 356000 393 000

18.7 20.4 24.0 19.6 24.7 7.1 6.4 5.3 4.1 3.9 4.0 4.5 6.1 6.1 6.2 6.6

160

E. Mushina et al./Applied

Catalysis A: General 166 (1998) 153-161

tion - MJM,, is in the 18-25 range. In this case, number average molecular mass does not exceed 20000 and the nature of the modifying metal almost does not effect molecular mass characteristics. In the case of titanium-magnesium catalysts, the resulting PE is characterised by a narrow molecular mass distribution (MJM?,= 4-7),the nature of oligomerizing component of the catalyst markedly affecting molecular mass of the polymer. This effect is especially distinct at low concentrations of hydrogen in the reaction gas, when the transition from organonickel to organozirconium compound is accompanied by an increase in the number average molecular mass by ca. 2.5 times. 3.3. Diene polymerization complex catalysts

with bicenter metal-

It has been shown recently that the silica-gel supported titanium-magnesium catalyst in combination with triisobutylaluminum is an effective catalyst for trans-polymerization of butadiene at a molar ratio Al/Ti = lo-20 [20]. The resulting polymer contains 98 wt% of truns-units and is a crystalline material. Polymerization of isoprene also produces truns-polymer. The rate of polymerization of butadiene increases as a Al/T1 ratio grows from 5 to 20. Further increase in this ratio does not affect the rate of the process. However, an increase in the Al/Ti molar ratio is accompanied by an increase in the content of cis-units in the polymer. As an extension of these researches, we studied polymerization of dienes, mainly butadiene, using bicenter catalysts of two types - Ti/Mg/SiO* and a chromium catalyst modified by oligodienyl organoaluminum compounds of zirconium and nickel. Tables 8 and 9 show the data on microstructure of the prepared polymers. Among the studied modifying additives nickel-containing complex shows the highest effect on the structure and kinetics of polymerization. The polymers, prepared with chromiumcontaining catalyst at 20°C contain more than 80 wt% of 1,4-cis-units. The effect of zirconiumcontaining component on the microstructure of polybutadiene is markedly smaller than that of nickelcontaining component. The content of the fractions of the polymer soluble and insoluble in boiling hexane were determined by

Table 8 Structure of polybutadiene with chromium-containing catalyst modified by oligodienyl zirconium and nickel compounds (according to IR-spectroscopy). Concentration of butadiene 2 molll Metal ratio (mol/mol)

ZrKr Zr/Cr NilCr Ni/Cr

= = = =

1.O 1.0 0.3 0.3

Temperature/ “C 20 60 20 60

Content of units/ wt% c,is- 1,4

trans. 1.4

1.2.

43 26 88 12

54 71 6 83

3 3 6 5

Table 9 Structure of polybutadiene with titanium-magnesium catalyst and with the same catalyst modified by oligodienyl zirconium and nickel compounds (according to IR-spectroscopy). Concentration of butadiene - 2 mol/l; Al/Ti = 20 mol/mol; 20°C Catalytic system

TiNg Ti/Mg + Zr Ti/Mg + Ni

Metal ratio (moVmo1)

Zr/Ti = 0.5 Zr/Ti = 1.0 Ni/Ti = 0.5

Content of units/ wt% cis- 1,4

tram 1,4

1.2.

8 10 18 31

83 81 70 58

9 9 12 11

fractionation of polybutadiene. It was found that the fraction of the polymer soluble in hot hexane contains only cis- 1,4-units, whereas the insoluble fraction contains trans-1.4-units. These results and the data of DSC [20] allow us to conclude that the polymers prepared using bicenter catalysts are the mixture of cis- and trans-polymers formed by different active centers. It was shown by X-ray diffraction analysis [21] that supermolecular structure of partially crystalline trans1,4-polybutadiene is unconventional. In addition to amorphous and crystalline phase components, which are conventional for the flexible-chain polymer, the prepared polymer contains also a considerable amount (up to 30 wt%) of mesomorphous phase, which was found to belong to a rare low-temperature condismesomorphic state [22]. Thus, the use of bicenter catalysts makes it possible to prepare homogeneous mixtures of cis- and transpolymers, which are of indubitable interest for practical application.

E. Mushina et al/Applied

Catalysis A: General

Conclusions Zirconiumand nickel-organoaluminum compounds bearing oligodienyl ligands were synthesized and their structure and composition were studied. It was shown that (i-C4H9)2A1Cl forms with these oligodienyl compounds complexes, which contain bridge structures with metalchloride bonds. Medium-density (0.940-0.945 g/cm3) PE was prepared by gas-phase polymerization of ethene using bicenter supported catalysts. It is found that titanium-magnesium catalysts modified by zirconium-organialuminum compounds are the most active in ethene polymerization. Bicenter metal complex catalysts are highly effective in diene polymerization. Microstructure of the resulting polymer is determined by composition of the catalyst and polymerization temperature. The prepared polymers represent mixtures of cis- and truns-units.

Acknowledgements The financial support of the Russian Foundation for Basic Research (RFBR, Grant No. 07-03-32827a) as well as the support of RFBR and German Research Society (joint Grant No. 96-03-00066) is gratefully acknowledged. Thanks are also due to Drs. G. Bondarenko, T. Lebedeva, and Yu. Bit-Gevorgisov for helpful experimental assistance.

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