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29. Highly Isospecific Heterogeneous Metallocene Catalysts Activated by Ordinary Alkylaluminums
307
29. Highly Isospecific Heterogeneous Metallocene Catalysts Activated by Ordinary Alkylaluminums
KAZUO SOGA Japan Advanced Institute of Science and Technology, Hokuriku, 15 Asahidai, Tatsunokuchi, Ishikawa Pref. 923-12, Japan ABSTRACT Tetrachlorosilane or 1,1,2,2-tetrabromoethane was reacted with the surface hydroxyl . groups of silica gel and the resulting chemically modified silica gel was brought into contact with lithium salt of indene. The catalyst precursors thus prepared were then reacted with zirconium tetrachloride to obtain the immobilized heterogeneous metallocene catalysts. Polymerization of propene was conducted with them using either methylalumoxane or common trialkylaluminums as cocatalyst. Since the catalysts may contain a mixture of meso and racemic isomers which give atactic and isotactic polypropene, the polymer produced was fractionated by extracting with boiling heptane. It was found that the catalysts can be easily activated by ordinary trialkylaluminums to give highly isotactic polypropene with the melting point as high as over 162 “C. Similar catalysts were also prepared using fluorene as ligand, which gave not syndiotactic but highly isotactic polypropene.
INTRODUCTION Poly(a-olefins) of any structure (isotactic, hemiisotactic, syndiotactic and atactic) can be obtained with metallocene catalysts simply by tailoring the stereorigid catalyst precursor, basically according to the local symmetry. Much effort has been recently paid to modify the metallocene catalysts for partial use. It was demonstrated that interconnection of a pair of ligands with single-bridge causes a marked increase in the isotacticity as well as molecular weight of polypropene’.’’. Immobilization of metallocene on the solid surface is also in progress. We have already reported3’ that metallocene catalysts supported on Al,O,, MgCl,, MAO-treated SiO, etc. are easily activated by ordinary alkylaluminums. Whereas, Kaminsky et al.4) obtained highly isotactic polypropene with high molecular weights using a single-phase catalyst composed of Et(Ind),ZrCI,, MA0 and SO,.
308 K . Soga
More recently, we have developed a new type of highly isospecific SiO, supported metallocene catalysts which can be activated by ordinary alkylaluminums. EXPERIMENTAL Materials: Propene and toluene of research grade purity commercially obtained from Takachiho Chem. Co. were further purified according to the usual procedures. SiO, (Fuji Davison Co. # 952) was calcined at 200, 400 or 900 "C for 6 h under a reduced pressure. (CH,),Si(Ind),ZrCI,, Et[IndH,],ZrCI,, iPr(Flu)(Cp)ZrCI, were prepared according to the literat~re~"'~'. Methylalumoxane (MAO) and alkylaluminums were donated from Tosoh Akzo Co. The other chemicals of research grade purity were commercially obtained and used without further purification. Preparation of Supported Catalysts: The synthetic procedure of the CI,Zr(Ind),Si-SiO, catalyst is described below as an example. A solution of SiO, (2.5 mmol) in toluene was dropwise added to a suspension of 4.3 g of SiO, in 70 cm3 of toluene, followed by refluxing for 48 h under agitating with a magnetic stirrer. Modified SiO, was separated by filtration and washed with a large quantity of THF. Then, to the SiO, in 30cm' of THF was dropwise added a suspension of lithium salt of indene (5 mmol) in THF at 0 "C under nitrogen atmosphere. The mixture was heated up to room temperature and kept standing for 12 h with a vigorous stirring. The solid product was separated and washed with a large amount of THF to obtained the catalyst precursor. The catalyst precursor was brought into contact with a solution of Li(n-C,H,) (5.5 mmol) in n-hexane, followed by reacting with
X I , 2THF (2.5 mmol in THF) at room temperature for 12 h. The resulting solid product was separated, washed with a large quantity of THF and diethylether and finally evaporated to dryness under vacuum to obtain the CI,Zr(Ind),Si-SiO, (I) catalyst. The procedure is schematically shown in Figure 1.
lndene
CtF'
/ 7 -7 7 /"
s102
s102
L1-lndene
I
lndene
\ /
A
77
7
sio2
Eapplw~tPi8uarallOn
Filtering 6 Washlng
''
77
SIO*
SICI,
\
Lblndene Indene-LI Indene Indene \ / \Sl' SI / \ ZrC14.2THF 2Ll(n-C4H ) THF,r.f.
( 5 mmol ) Lithium salt of lndene
THF, Stirring at 0%
s102
(5 5 mmol)
tWashlng 6 Drylng
2Un-C4Hd Sbrring at r t for 12h
Washlng
Stirring at r t
(Zr content 5 9 104mol(rr)/g-Si02) by ICP
Figure 1
Scheme and procedure
Of
catalyst (I)
preparation
'Or
29. Highly lsospecific Heterogeneous Metallocene Catalysts
309
The CI,Zr(Ind),Et-SiO, (11) catalyst was prepared using tetrabromoethane in place of SiCI, (Figure 2). Whereas, the CI,Zr(Flu),Si-SiO, (111) catalyst was prepared according to the procedure shown in Figure 1 using fluorene i n place of indene.
(11)
2Ll( n-C4H9)
"\ /c' 7r
Activation
-
/-\
Li
lndene lndene M A 0 or TlBA
Toluene
)-(
u sio,
Figure 2
ZrCi4 2THF
THF,r.l.
*
IndeFe lndene Li
Y P
sio2
Scheme of catalyst (11) preparation.
Polymerization and Analytical Procedures : Polymerization of propene was conducted at 40°C in a 100cm3 stainless steel reactor equipped with a magnetic stirrer using toluene as solvent. Polymerization was terminated by adding acidic methanol and the polymer obtained was adequately washed with methanol, followed by enacting with boiling 1,2,4-tnchlorobenzene to remove the catalyst ash. Polymerization of propene was also carried out using the corresponding homogeneous catalysts for reference. The contents of Zr in the catalysts were analyzed by an ICP-OES-spectrometer (Jobin Yvon, JY-70-PLUS). The molecular mass distributions (MMD) of polymers were measured at 145 "C by gel-permeation chromatography (GPC, Waters 15OC) using o-dichlorobenzene as solvent. The melting points (Tm) of polymers were measured on samples which had been previously melted at a heating rate of 10 "C/min. The microstructure of polymers was mainly determined by I3C NMR. The spectrum was recorded at 120°C with a JEOL GX-270 spectrometer operating at 67.8 MHz. (9/1 by vol) up to 10 wt-%. Polymers were dissolved in 1,2,4-trichlorobenzene/benzene-d6 RESULTS AND DISCUSSION The catalysts (I) and (11) are considered to contain both aspecific (meso) and isospecific (racemic) active sites. The polymers obtained were, therefore, fractionated by extracting with boiling heptane. The results of propene polymerization over the catalysts(1) and (11) together with some analytical data of polymers are shown in Tables 1 and 2, where the results obtained with the corresponding homogeneous catalysts are also indicated for reference.
310 K . Soga
Table I
Results of propene polymerization with the C1,Zr(1nd),Si-SiO2 catalyst".
Catalyst
Activity in Mw Cocatalyst Amount of Yield cocatalyst (in g) kg(PP)/mol(Zr) (lO*gmol'l) (in mmol)
(CH,),Si(lnd),ZrCl,
MA0
5
0.37
74
3.0
MA0 MA0
1
0.32
5.4
34.0
3
0.33
5.6
Tm
1.1. iso.pentads (in %) mmmm(%)
(in "C)
-
142.1
32
83.3
153.0 159.2
68
94.3
156.1 162.3
67
MA0
10
0.36
6.1
-
156.7 163.0
68
AI(i-C,,HJ,
1
0.22
3.7
72.0
153.9 158.0
80
AI(i-C&),
3
0.25
4.3
-
158.6 162.2
76
Cl&(Ind),Si-SiO,
98.0
a) SiO, was calcined at 4WoC
Table 2
Results of propene polymerization with the CI,Zr(Ind),Et-SiO, catalyst"
Catalyst
Et[IndH,],ZrCI,
ClJr(Ind),Et-SiO,
Cocatalyst
Amount of cocatdyst (in mmol)
Yield Mw (in g) (lo4gmol")
MA0
3
2.07
MA0 AKi-C.,&), Al(n-C,HJ, AKC,Y), WCHJ,
1
0.47
1
0.40
1
0.3
Tm in"^)
I 1 1.0
1.1.
iso.pentads
(in o/o)
mmmm(%)
-
71.0
149.9 160.0
46
93.0
158.2
55
91.1
1
0.18 0.21
157.7 153.2 161.2
67 68
I
0.1 1
156.8 162.1
61
48.5
-
-
a) SiO, was calcined at 400 "C
It is instantaneously obvious from Tables 1, 2 and Figure 3 that the isotactic fraction (1.1.) as well as molecular weight, [mmmm] pentad and melting point of isotactic PP drastically increase by using the present immobilized metallocene catalysts. Besides, the supported catalysts can be activated by ordinary alkylaluminums. Among the trialkylaluminums used in the present study, Al(i-C4HJ3 showed the highest activity.
29. Highly Isospecific Heterogeneous Metallocene Catalysts 3 1 1
-
I
a) 1 mmol of Al(i-C4Hg)3
b) 3 rnmol of Al(i-C4Hg)3
-----.c) 1 mmol of MA0 d) 3 mmol of MA0
/
e) 10 mrnol of MA0
\ 140 150 1GO 170 180 190 T e m p e r a t u r e ("C)
Figure 3
DSC charts of isotactic PP (boiling heptane insoluble fraction) obtained by changing the amount of cocatalyst.
To check the microstructure of isotactic PP in more detail, some of the boiling heptane insoluble polymers were analyzed by 1 3C NMR, which did not display any peak assignable to the irregular propene units resulted from 1,3-insertion. The disappearance of such irregular units in addition to the very high [mmmm] value might cause a marked increase in Tm.
312
K. Soga
Most of the supported metallocene catalysts reported so far have been devised to immobilize metallocenes on the solid surface utilizing the ionic interactions between the C1-ligands of metallocenes and the surface active sites. Whereas, in the present catalysts, zirconocene may be fixed on SiO, more rigidly as schematically illustrated in Figures 1 and 2. However, the present catalysts are supposed to possess two kinds of active species which differ in mobility as shown in Figure4.
ct f1 ,z\
ctZr , 'i Indene lndene /
fZ:
lndene Inde ....
lndene
\ / i"""'" Si
\ /
.Si.
SiOz
More rigidly immobilized style
SiOz Less lmmoblllzed s t y l e
(A)
Figure 4
\
(B)
Plausible structures of the CI,Zr(Ind),Si-SiO, catalyst.
In fact, most of the isotactic PP obtained here display two melting points. It is supposed, therefore, that the more rigidly fixed species (A) is responsible for the production of higher isotactic PP. To confirm it, three kinds of the CI,Zr(Ind),Si-SiO, catalysts were prepared using the SiO, calcined at 200, 400 and 900 "C, and polymerization of propene was conducted at 40 "C over them. Since the concentration of surface hydroxyl groups increases with a decrease in the calcinating temperature of SO,, it is expected that the fraction of (A) becomes predominant with decreasing the calcinating temperature. The results of propene polymerization (Table 3) are in good agreement with this consideration.
Table 3
Results of propene polymerization with the ClTr(Ind),SiSiO, catalyst using the SiO, calcined at different temperatures.
Calcinating
Cocatalyst
Temp. (in "C)
Amount of
Yield
Tm
1.1.
cocatalyst (in mmoi)
(in g)
(in "C)
(in %)
200
A1(i-C4W3
3
0.26
162.3 158.2
75
400 900
3
0.25
162.2 158.6
76
3
0.24
-
159.5
3
0.14
161.4
-
400
Al(i-C,Y), A1(i-C4W3 MA0 MA0
3
0.33
162.3 156.1
67
900
MA0
3
0.17
159.1
27
200
-
31 84
29. Highly lsospecific Heterogeneous Metallocene Catalysts
313
Polymerization of propene was then carried out at 40°C using the Cl,Zr(Flu),Si-SiO, (111) catalyst. The polymer obtained was fractionated by extracting with boiling heptane. In
Figure 5 are illustrated the I3C NMR spectra of (a) whole polymer, (b) boiling heptane soluble polymer and (c) boiling heptane insoluble polymer obtained with the CI,Zr(Flu),SiSiO, - A1(i-C4H& catalyst system.
,,I\
40
20
30
10
W"
.
3'5.
.
30.
2'5
20
15
10
Figure 5 "CNMR spectra of polypropene obtained with the CI,Zr(Ru),Si-SiO, catalyst : (a) whole polymer (b) boiling heptane soluble polymer (c) boiling heptane insoluble polymer.
, - - - . . -. . 35
. . .
30
25
20
15
ld
314
K . Soga
Surprisingly, the boiling heptane insoluble polymer (c) was found to be highly isotactic. Some additional data on the typical boiling heptane insoluble polymers are shown inTable4. Table 4
Results of propene polymerization with the CI,Zr(Flu),Si-SiO, catalyst”. ~ _ _ _
Cocatalyst
Amount of cocatdyst (in mmol)
Yield (in g)
Mw (lo4grnol.’)
Tm (in “c)
mmmm or rrrr (%)
i-Pr(Flu)(Cp)ZrCI,
MA0
13
3.03
3.9
123.0
r r r r = 77
CI,Zr(Flu),Si-SiO,
MA0 AI(i-C,HJ,
15 15
0.5 1 0.45
33
160.3 163.9
mmrnm = 96
Catalyst
a) SiO, was calcined at 400’C. x =??
However much more information should be necessary to speculate the structure of isospecific sites in the catalyst (Ill). In conclusion, it was found that highly isospecific heterogeneous metallocene catalysts, which are activated by ordinary trialkylaluminums, can be prepared by fixing the ligands on the surface of SiO,. A more detailed study on the improvement of both catalyst activity and isospecific selectivity is now in progress, the results of which will be published elsewhere.
REFERENCES 1. T.Mise, S.Miya, H.Yamazaki, Chemistry Letters, 1853 (1989) 2. W.Speleck, M.Antberg, J.Rohrmann, A.Winter, B.Bachmann, P.Kiprof, J.Behm, W.A.Hemnann, Angew. Chem. Int. Et. Engl., 31, 1347 (1992) 3. K.Soga, M.Kaminaka, Makromol. Chem., 194, 1745 (1993) 4. W.Kaminsky, F.Renner, Makromol. Chem., Rapid Commun., 14, 239 (1993) 5. F.R.W.P.Wild, M.Wasiucionek, G.Huttner, H.H.Brintzinger, J. Organomet. Chem., 63, 288 (1985) 6. J.A.Ewen, M.J.Elder, Makromol. Chem., Macromol. Symp., 48/49, 253 (1991)
29. Highly Isospecific Heterogeneous Metallocene Catalysts Activated by Ordinary Alkylaluminums
KAZUO SOGA Japan Advanced Institute of Science and Technology, Hokuriku, 15 Asahidai, Tatsunokuchi, Ishikawa Pref. 923-12, Japan ABSTRACT Tetrachlorosilane or 1,1,2,2-tetrabromoethane was reacted with the surface hydroxyl . groups of silica gel and the resulting chemically modified silica gel was brought into contact with lithium salt of indene. The catalyst precursors thus prepared were then reacted with zirconium tetrachloride to obtain the immobilized heterogeneous metallocene catalysts. Polymerization of propene was conducted with them using either methylalumoxane or common trialkylaluminums as cocatalyst. Since the catalysts may contain a mixture of meso and racemic isomers which give atactic and isotactic polypropene, the polymer produced was fractionated by extracting with boiling heptane. It was found that the catalysts can be easily activated by ordinary trialkylaluminums to give highly isotactic polypropene with the melting point as high as over 162 “C. Similar catalysts were also prepared using fluorene as ligand, which gave not syndiotactic but highly isotactic polypropene.
INTRODUCTION Poly(a-olefins) of any structure (isotactic, hemiisotactic, syndiotactic and atactic) can be obtained with metallocene catalysts simply by tailoring the stereorigid catalyst precursor, basically according to the local symmetry. Much effort has been recently paid to modify the metallocene catalysts for partial use. It was demonstrated that interconnection of a pair of ligands with single-bridge causes a marked increase in the isotacticity as well as molecular weight of polypropene’.’’. Immobilization of metallocene on the solid surface is also in progress. We have already reported3’ that metallocene catalysts supported on Al,O,, MgCl,, MAO-treated SiO, etc. are easily activated by ordinary alkylaluminums. Whereas, Kaminsky et al.4) obtained highly isotactic polypropene with high molecular weights using a single-phase catalyst composed of Et(Ind),ZrCI,, MA0 and SO,.
308 K . Soga
More recently, we have developed a new type of highly isospecific SiO, supported metallocene catalysts which can be activated by ordinary alkylaluminums. EXPERIMENTAL Materials: Propene and toluene of research grade purity commercially obtained from Takachiho Chem. Co. were further purified according to the usual procedures. SiO, (Fuji Davison Co. # 952) was calcined at 200, 400 or 900 "C for 6 h under a reduced pressure. (CH,),Si(Ind),ZrCI,, Et[IndH,],ZrCI,, iPr(Flu)(Cp)ZrCI, were prepared according to the literat~re~"'~'. Methylalumoxane (MAO) and alkylaluminums were donated from Tosoh Akzo Co. The other chemicals of research grade purity were commercially obtained and used without further purification. Preparation of Supported Catalysts: The synthetic procedure of the CI,Zr(Ind),Si-SiO, catalyst is described below as an example. A solution of SiO, (2.5 mmol) in toluene was dropwise added to a suspension of 4.3 g of SiO, in 70 cm3 of toluene, followed by refluxing for 48 h under agitating with a magnetic stirrer. Modified SiO, was separated by filtration and washed with a large quantity of THF. Then, to the SiO, in 30cm' of THF was dropwise added a suspension of lithium salt of indene (5 mmol) in THF at 0 "C under nitrogen atmosphere. The mixture was heated up to room temperature and kept standing for 12 h with a vigorous stirring. The solid product was separated and washed with a large amount of THF to obtained the catalyst precursor. The catalyst precursor was brought into contact with a solution of Li(n-C,H,) (5.5 mmol) in n-hexane, followed by reacting with
X I , 2THF (2.5 mmol in THF) at room temperature for 12 h. The resulting solid product was separated, washed with a large quantity of THF and diethylether and finally evaporated to dryness under vacuum to obtain the CI,Zr(Ind),Si-SiO, (I) catalyst. The procedure is schematically shown in Figure 1.
lndene
CtF'
/ 7 -7 7 /"
s102
s102
L1-lndene
I
lndene
\ /
A
77
7
sio2
Eapplw~tPi8uarallOn
Filtering 6 Washlng
''
77
SIO*
SICI,
\
Lblndene Indene-LI Indene Indene \ / \Sl' SI / \ ZrC14.2THF 2Ll(n-C4H ) THF,r.f.
( 5 mmol ) Lithium salt of lndene
THF, Stirring at 0%
s102
(5 5 mmol)
tWashlng 6 Drylng
2Un-C4Hd Sbrring at r t for 12h
Washlng
Stirring at r t
(Zr content 5 9 104mol(rr)/g-Si02) by ICP
Figure 1
Scheme and procedure
Of
catalyst (I)
preparation
'Or
29. Highly lsospecific Heterogeneous Metallocene Catalysts
309
The CI,Zr(Ind),Et-SiO, (11) catalyst was prepared using tetrabromoethane in place of SiCI, (Figure 2). Whereas, the CI,Zr(Flu),Si-SiO, (111) catalyst was prepared according to the procedure shown in Figure 1 using fluorene i n place of indene.
(11)
2Ll( n-C4H9)
"\ /c' 7r
Activation
-
/-\
Li
lndene lndene M A 0 or TlBA
Toluene
)-(
u sio,
Figure 2
ZrCi4 2THF
THF,r.l.
*
IndeFe lndene Li
Y P
sio2
Scheme of catalyst (11) preparation.
Polymerization and Analytical Procedures : Polymerization of propene was conducted at 40°C in a 100cm3 stainless steel reactor equipped with a magnetic stirrer using toluene as solvent. Polymerization was terminated by adding acidic methanol and the polymer obtained was adequately washed with methanol, followed by enacting with boiling 1,2,4-tnchlorobenzene to remove the catalyst ash. Polymerization of propene was also carried out using the corresponding homogeneous catalysts for reference. The contents of Zr in the catalysts were analyzed by an ICP-OES-spectrometer (Jobin Yvon, JY-70-PLUS). The molecular mass distributions (MMD) of polymers were measured at 145 "C by gel-permeation chromatography (GPC, Waters 15OC) using o-dichlorobenzene as solvent. The melting points (Tm) of polymers were measured on samples which had been previously melted at a heating rate of 10 "C/min. The microstructure of polymers was mainly determined by I3C NMR. The spectrum was recorded at 120°C with a JEOL GX-270 spectrometer operating at 67.8 MHz. (9/1 by vol) up to 10 wt-%. Polymers were dissolved in 1,2,4-trichlorobenzene/benzene-d6 RESULTS AND DISCUSSION The catalysts (I) and (11) are considered to contain both aspecific (meso) and isospecific (racemic) active sites. The polymers obtained were, therefore, fractionated by extracting with boiling heptane. The results of propene polymerization over the catalysts(1) and (11) together with some analytical data of polymers are shown in Tables 1 and 2, where the results obtained with the corresponding homogeneous catalysts are also indicated for reference.
310 K . Soga
Table I
Results of propene polymerization with the C1,Zr(1nd),Si-SiO2 catalyst".
Catalyst
Activity in Mw Cocatalyst Amount of Yield cocatalyst (in g) kg(PP)/mol(Zr) (lO*gmol'l) (in mmol)
(CH,),Si(lnd),ZrCl,
MA0
5
0.37
74
3.0
MA0 MA0
1
0.32
5.4
34.0
3
0.33
5.6
Tm
1.1. iso.pentads (in %) mmmm(%)
(in "C)
-
142.1
32
83.3
153.0 159.2
68
94.3
156.1 162.3
67
MA0
10
0.36
6.1
-
156.7 163.0
68
AI(i-C,,HJ,
1
0.22
3.7
72.0
153.9 158.0
80
AI(i-C&),
3
0.25
4.3
-
158.6 162.2
76
Cl&(Ind),Si-SiO,
98.0
a) SiO, was calcined at 4WoC
Table 2
Results of propene polymerization with the CI,Zr(Ind),Et-SiO, catalyst"
Catalyst
Et[IndH,],ZrCI,
ClJr(Ind),Et-SiO,
Cocatalyst
Amount of cocatdyst (in mmol)
Yield Mw (in g) (lo4gmol")
MA0
3
2.07
MA0 AKi-C.,&), Al(n-C,HJ, AKC,Y), WCHJ,
1
0.47
1
0.40
1
0.3
Tm in"^)
I 1 1.0
1.1.
iso.pentads
(in o/o)
mmmm(%)
-
71.0
149.9 160.0
46
93.0
158.2
55
91.1
1
0.18 0.21
157.7 153.2 161.2
67 68
I
0.1 1
156.8 162.1
61
48.5
-
-
a) SiO, was calcined at 400 "C
It is instantaneously obvious from Tables 1, 2 and Figure 3 that the isotactic fraction (1.1.) as well as molecular weight, [mmmm] pentad and melting point of isotactic PP drastically increase by using the present immobilized metallocene catalysts. Besides, the supported catalysts can be activated by ordinary alkylaluminums. Among the trialkylaluminums used in the present study, Al(i-C4HJ3 showed the highest activity.
29. Highly Isospecific Heterogeneous Metallocene Catalysts 3 1 1
-
I
a) 1 mmol of Al(i-C4Hg)3
b) 3 rnmol of Al(i-C4Hg)3
-----.c) 1 mmol of MA0 d) 3 mmol of MA0
/
e) 10 mrnol of MA0
\ 140 150 1GO 170 180 190 T e m p e r a t u r e ("C)
Figure 3
DSC charts of isotactic PP (boiling heptane insoluble fraction) obtained by changing the amount of cocatalyst.
To check the microstructure of isotactic PP in more detail, some of the boiling heptane insoluble polymers were analyzed by 1 3C NMR, which did not display any peak assignable to the irregular propene units resulted from 1,3-insertion. The disappearance of such irregular units in addition to the very high [mmmm] value might cause a marked increase in Tm.
312
K. Soga
Most of the supported metallocene catalysts reported so far have been devised to immobilize metallocenes on the solid surface utilizing the ionic interactions between the C1-ligands of metallocenes and the surface active sites. Whereas, in the present catalysts, zirconocene may be fixed on SiO, more rigidly as schematically illustrated in Figures 1 and 2. However, the present catalysts are supposed to possess two kinds of active species which differ in mobility as shown in Figure4.
ct f1 ,z\
ctZr , 'i Indene lndene /
fZ:
lndene Inde ....
lndene
\ / i"""'" Si
\ /
.Si.
SiOz
More rigidly immobilized style
SiOz Less lmmoblllzed s t y l e
(A)
Figure 4
\
(B)
Plausible structures of the CI,Zr(Ind),Si-SiO, catalyst.
In fact, most of the isotactic PP obtained here display two melting points. It is supposed, therefore, that the more rigidly fixed species (A) is responsible for the production of higher isotactic PP. To confirm it, three kinds of the CI,Zr(Ind),Si-SiO, catalysts were prepared using the SiO, calcined at 200, 400 and 900 "C, and polymerization of propene was conducted at 40 "C over them. Since the concentration of surface hydroxyl groups increases with a decrease in the calcinating temperature of SO,, it is expected that the fraction of (A) becomes predominant with decreasing the calcinating temperature. The results of propene polymerization (Table 3) are in good agreement with this consideration.
Table 3
Results of propene polymerization with the ClTr(Ind),SiSiO, catalyst using the SiO, calcined at different temperatures.
Calcinating
Cocatalyst
Temp. (in "C)
Amount of
Yield
Tm
1.1.
cocatalyst (in mmoi)
(in g)
(in "C)
(in %)
200
A1(i-C4W3
3
0.26
162.3 158.2
75
400 900
3
0.25
162.2 158.6
76
3
0.24
-
159.5
3
0.14
161.4
-
400
Al(i-C,Y), A1(i-C4W3 MA0 MA0
3
0.33
162.3 156.1
67
900
MA0
3
0.17
159.1
27
200
-
31 84
29. Highly lsospecific Heterogeneous Metallocene Catalysts
313
Polymerization of propene was then carried out at 40°C using the Cl,Zr(Flu),Si-SiO, (111) catalyst. The polymer obtained was fractionated by extracting with boiling heptane. In
Figure 5 are illustrated the I3C NMR spectra of (a) whole polymer, (b) boiling heptane soluble polymer and (c) boiling heptane insoluble polymer obtained with the CI,Zr(Flu),SiSiO, - A1(i-C4H& catalyst system.
,,I\
40
20
30
10
W"
.
3'5.
.
30.
2'5
20
15
10
Figure 5 "CNMR spectra of polypropene obtained with the CI,Zr(Ru),Si-SiO, catalyst : (a) whole polymer (b) boiling heptane soluble polymer (c) boiling heptane insoluble polymer.
, - - - . . -. . 35
. . .
30
25
20
15
ld
314
K . Soga
Surprisingly, the boiling heptane insoluble polymer (c) was found to be highly isotactic. Some additional data on the typical boiling heptane insoluble polymers are shown inTable4. Table 4
Results of propene polymerization with the CI,Zr(Flu),Si-SiO, catalyst”. ~ _ _ _
Cocatalyst
Amount of cocatdyst (in mmol)
Yield (in g)
Mw (lo4grnol.’)
Tm (in “c)
mmmm or rrrr (%)
i-Pr(Flu)(Cp)ZrCI,
MA0
13
3.03
3.9
123.0
r r r r = 77
CI,Zr(Flu),Si-SiO,
MA0 AI(i-C,HJ,
15 15
0.5 1 0.45
33
160.3 163.9
mmrnm = 96
Catalyst
a) SiO, was calcined at 400’C. x =??
However much more information should be necessary to speculate the structure of isospecific sites in the catalyst (Ill). In conclusion, it was found that highly isospecific heterogeneous metallocene catalysts, which are activated by ordinary trialkylaluminums, can be prepared by fixing the ligands on the surface of SiO,. A more detailed study on the improvement of both catalyst activity and isospecific selectivity is now in progress, the results of which will be published elsewhere.
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