more than 100 h of polymerization time they are still active. Bridged bis(fluorenyl)
zirconocenes are also reported to be very active [73]. Polyethylenes synthesized
by metallocene/MAO catalysts have a molecular weight distribution (M w /M n )
of 2 and show 0.9–1.2 methyl side groups, 1.1–1.8 vinyl and 0.2 trans-vinyl
groups per 1,000 C atoms in the backbone polymer chain. The molecular weight
of metallocene polyethylenes varies in a wide range between 18,000 and 1.5 million
and can be easily lowered by increasing the temperature, raising the metallocene/
ethene ratio, or by adding small amounts of hydrogen (0.1–2 mol%) [74]. The
molecular weight distribution can be decreased down to 1.1 by living polymerization
using bis(phenoxy-imine)titanium complexes (FI-catalysts) or other half-sandwich
complexes [75–78].
For an industrial use, it can be necessary to support the MAO cocatalyst on silica
or alumina. Silica with up to 30 wt% of MAO is obtained. In such a case, a
Table 2 Comparison of ethene polymerization
a with different metallocene/MAO catalysts at the
same polymerization conditions
Metallocene
b
Activity
c
Molecular weight
(g/mol)
Cp 2 TiCl 2
34,200
400,000
Cp 2 ZrCl 2
60,900
620,000
Cp 2 HfCl 2
4,200
700,000
Cp 2 TiMe 2
1,200
500,000
Cp 2 ZrMe 2
14,000
730,000
Cp* 2 ZrCl 2
1,300
1,500,000
(NmCp) 2 ZrCl 2
12,200
1,000,000
[O(SiMeCp) 2 ]ZrCl 2
57,800
930,000
[En(IndH 4 ) 2 ]ZrCl 2
22,200
1,000,000
[En(Ind) 2 ]ZrCl 2
12,000
350,000
[En(Ind) 2 ]HfCl 2
2,900
480,000
[En(2,4,7-Me 3 Ind) 2 ]ZrCl 2
78,000
190,000
[Me 2 Si(Ind) 2 ]ZrCl 2
36,900
260,000
[Ph 2 Si(Ind) 2 ]ZrCl 2
20,200
320,000
[Bz 2 Si(Ind) 2 ]ZrCl 2
12,000
350,000
[Me 2 Si(IndH 4 ) 2 ]ZrCl 2
30,200
900,000
[Me 2 Si(2,4,7-Me 3 Ind) 2 ]ZrCl 2
111,900
250,000
[Me 2 Si(2Me-4Ph-Ind) 2 ]ZrCl 2
16,600
730,000
[Me 2 C(Ind)(Cp)]ZrCl 2
15,500
25,000
[Ph 2 C(Ind)(Cp)]ZrCl 2
3,300
18,000
[Me 2 C(Ind)(3MeCp)]ZrCl 2
2,700
30,000
[Me 2 C(Flu)(Cp)]ZrCl 2
2,000
500,000
[Ph 2 C(Flu)(Cp)]ZrCl 2
2,800
630,000
[Me 2 C(Flu)(Cp)]HfCl 2
890
560,000
a
Polymerization conditions: ethene pressure 2.5 bar, temperature 30
C, [metallocene]
6.25 Â 10
À6 mol, metallocene/MAO ratio 250, solvent toluene
b
Cp cyclopentadienyl, Me methyl, Ind indenyl, IndH 4 tetrahydroindenyl, En C 2 H 4 , Flu fluorenyl,
NmCp neomenthyl cyclopentadienyl, Bz benzyl
c
Activity is expressed as kg PE /(mol metallocene h [ethene])
Methylaluminoxane: Key Component for New Polymerization Catalysts
11
zirconocenes are also reported to be very active [73]. Polyethylenes synthesized
by metallocene/MAO catalysts have a molecular weight distribution (M w /M n )
of 2 and show 0.9–1.2 methyl side groups, 1.1–1.8 vinyl and 0.2 trans-vinyl
groups per 1,000 C atoms in the backbone polymer chain. The molecular weight
of metallocene polyethylenes varies in a wide range between 18,000 and 1.5 million
and can be easily lowered by increasing the temperature, raising the metallocene/
ethene ratio, or by adding small amounts of hydrogen (0.1–2 mol%) [74]. The
molecular weight distribution can be decreased down to 1.1 by living polymerization
using bis(phenoxy-imine)titanium complexes (FI-catalysts) or other half-sandwich
complexes [75–78].
For an industrial use, it can be necessary to support the MAO cocatalyst on silica
or alumina. Silica with up to 30 wt% of MAO is obtained. In such a case, a
Table 2 Comparison of ethene polymerization
a with different metallocene/MAO catalysts at the
same polymerization conditions
Metallocene
b
Activity
c
Molecular weight
(g/mol)
Cp 2 TiCl 2
34,200
400,000
Cp 2 ZrCl 2
60,900
620,000
Cp 2 HfCl 2
4,200
700,000
Cp 2 TiMe 2
1,200
500,000
Cp 2 ZrMe 2
14,000
730,000
Cp* 2 ZrCl 2
1,300
1,500,000
(NmCp) 2 ZrCl 2
12,200
1,000,000
[O(SiMeCp) 2 ]ZrCl 2
57,800
930,000
[En(IndH 4 ) 2 ]ZrCl 2
22,200
1,000,000
[En(Ind) 2 ]ZrCl 2
12,000
350,000
[En(Ind) 2 ]HfCl 2
2,900
480,000
[En(2,4,7-Me 3 Ind) 2 ]ZrCl 2
78,000
190,000
[Me 2 Si(Ind) 2 ]ZrCl 2
36,900
260,000
[Ph 2 Si(Ind) 2 ]ZrCl 2
20,200
320,000
[Bz 2 Si(Ind) 2 ]ZrCl 2
12,000
350,000
[Me 2 Si(IndH 4 ) 2 ]ZrCl 2
30,200
900,000
[Me 2 Si(2,4,7-Me 3 Ind) 2 ]ZrCl 2
111,900
250,000
[Me 2 Si(2Me-4Ph-Ind) 2 ]ZrCl 2
16,600
730,000
[Me 2 C(Ind)(Cp)]ZrCl 2
15,500
25,000
[Ph 2 C(Ind)(Cp)]ZrCl 2
3,300
18,000
[Me 2 C(Ind)(3MeCp)]ZrCl 2
2,700
30,000
[Me 2 C(Flu)(Cp)]ZrCl 2
2,000
500,000
[Ph 2 C(Flu)(Cp)]ZrCl 2
2,800
630,000
[Me 2 C(Flu)(Cp)]HfCl 2
890
560,000
a
Polymerization conditions: ethene pressure 2.5 bar, temperature 30
C, [metallocene]
6.25 Â 10
À6 mol, metallocene/MAO ratio 250, solvent toluene
b
Cp cyclopentadienyl, Me methyl, Ind indenyl, IndH 4 tetrahydroindenyl, En C 2 H 4 , Flu fluorenyl,
NmCp neomenthyl cyclopentadienyl, Bz benzyl
c
Activity is expressed as kg PE /(mol metallocene h [ethene])
Methylaluminoxane: Key Component for New Polymerization Catalysts
11