Polymerization of ethylene and propylene with homogeneous titanocene catalysts modified by trimethylsilanol

~

Eur. Polvm. J. Vol. 30, No. I1, pp. 1295 1299, 1994 Copyright ~? 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0014-3057/94 $7.00 + 0.00

Pergamon

0014-3057(94)E0079-J

POLYMERIZATION OF ETHYLENE A N D PROPYLENE WITH H O M O G E N E O U S TITANOCENE CATALYSTS M O D I F I E D BY TRIMETHYLSILANOL H Y U N JOON K1M1 and LuIz CLAUDIO DE SANTA MARIA2. tSamsung General Chemicals Co. Ltd, Chemical Technology Center, Korea and "~lnstituto de Cirncias, Escola Federal de Engenharia de Itajubfi_, Av. BPS, 1303-Itajub/t, MG 37500-000, Brasil

(Received 13 September 1993; accepted 10 November 1993)

Abstract--Polymerizations of ethylene and propylene were conducted with catalysts based on titanium compounds (TIC14 or CpTiCI 3) modified by trimethylsilanol (TMS). The convenient conditions of catalyst preparation and polymerization were investigated such as ageing time, Si/Ti mole ratio, catalyst concentration, type of alkylaluminum compound used as cocatalyst and AI/Ti mole ratio. The influence of these parameters on the homopolymerization of ethylene and propylene is then described in detail. The polymerization activities were found to be strongly dependent upon catalyst preparation and polymerization conditions. Electron paramagnetic resonance (EPR) analyses were conducted with different AI/Ti mole ratios for elucidating the influence of the Ti oxidation state on the catalyst properties. This work reports a plausible mechanism for the polymerization on the basis of these results.

INTRODUCTION Each year tremendous research efforts on ZieglerNatta catalysts are paid to improve the catalytic performance. These efforts have produced the new catalyst systems with superior properties. Although many researchers have been engaged in the study of this field and its industrial use has enormously expanded in the last decades, the catalyst behaviour is not completely understood yet. In spite of the new catalysts and processes that have been announced, intensive directed research is still developing towards the understanding of fundamentals of this process. The fundamental questions include a mechanistic comprehension of the influence of the catalyst type, additives and polymerization conditions on catalytic properties, molecular weight and molecular weight distribution etc. are not yet clear. The recent homogeneous Ziegler-Natta catalyst based on Cp2TiCI2 (Cp = cyclopendadienyl) and R2AIC1 (R = alkyl) has shown a very low activity for ethylene polymerization due to bimolecular deactivation caused by reductive metathesis [1]. Instead of this, much effort has been paid to modify this type of catalyst. Kaminsky et al. [2] have developed an extremely high active catalyst substituting Ti for Zr and using methylaluminoxane (MAO) as co-catalyst. Jordan et al. [3] have found that some dicyclopentadienylzirconium alkyl complexes effectively catalyse ethylene polymerization in the absence of any cocatalyst. We have reported that the Cp2ZrCI2/SiO2 catalyst, which is prepared by supporting Cp2ZrC12 on the SiO2 modified with CI2Si(CH3) 2, gives polyethylene in a high yield using c o m m o n trialkylaluminums as cocatalysts [4].

*To whom all correspondence should be addressed.

Recently we have found that the homogeneous catalyst system composed of the mixture of a zirconocene compound and Si(CH3)3 OH is activated by c o m m o n trialkylalyminums [5]. Now we have prepared a kind of catalyst based on Ti compounds modified with Si(CH3)3OH which showed to be soluble in the diluent of polymerization. This paper reports the results of homopolymerizations of ethylene and propylene employing this new type of homogeneous catalyst. EXPERIMENTAL SECTION Materials

Toluene, propylene and ethylene of research grade purity (from Takachiho Chemical Co. Ltd) were further purified according to usual procedure. Si(CH3)3OH used in this study was distilled under nitrogen atmosphere after refluxi n , over molecular sieve 4/~ and stored over molecular sieve 4 A. The aluminum compounds and Ti compounds (TiCl4 and CpTiCl3) were commercially purchased and used without further purification. Polymerization procedure

The catalyst was prepared in situ for ethylene and propylene polymerizations, it used a 100cm 3 glass reactor equipped with a magnetic stirrer where 50 cm 3 of toluene, 0.1 mmol of Ti and a prescribed amount of Si(CH3)3OH was introduced. This solution was kept to age for a determined time at room temperature (r.t.), then the reactor was degassed, followed by the introduction of ethylene until saturation at atmosphere pressure and the cocatalyst solution was added. The ethylene was continuously fed during 10min at 40°C. The polymerization was terminated by adding a diluted hydrochloric acid solution in methanol. The precipitated polymer was washed with methanol, followed by drying in vacuo at 60cC for 6 hr. Polymerization of propylene was conducted in a 100 cm 3autoclave equipped with a magnetic stirrer, where given amounts of catalyst and cocatalyst in 30 cm 3 of toluene are introduced, followed by

1295

1296

HYUN JOON KIM and Lulz CLAUDIO DE SANTA MARIA Table 1. Effect of the Si(CH3)3OH/TiCI4mole ratio on the activity of ethylene polymerization~ Ran Si/Ti Yield m.p. No. mole ratio (g) CC) I 0 0.45 131.4 2 1.0 1.12 133.5 3 1.5 1.89 -4 2.0 2.25 132.8 5 2.5 0.25 -6 3.0 0.07 131.7 ~Polymerization was conducted using 10-~ mmol of TiCI4, 10 i mmol of AI(CH3)3, 50cm3 of toluene at 40C for 10min at Iatm.

a measured amount of propylene at liquid nitrogen temperature. The polymerization was carried out during 4 h r at 40°C. The polymerization was terminated by adding a diluted solution of hydrochloric acid in methanol. The precipitated polymer was washed with methanol, followed by drying in vacuo at 60°C for 6 hr.

Measurements Differential scanning colorimeter (DSC) measurements were made at a heating rate of 10°C/min. The ESR spectrum was taken in a Pyrex glass tube of 3 mm dia at r.t. on a JEOL-RE-3X ESR spectrometer with 100 x 103 cycles per sec field modulation. Mn(II) doped on MgO was used as standard to determine the G-values. The microstructures of polymers were mainly determined by t3C-NMR using a JEOL GX-270 spectrometer operating at 67.8 MHz. The samples were measured at 120°C employing odichlorobenzene as solvent and hexamethylsilane (HMDS) as internal standard.

RESULTS AND DISCUSSION

Ethylene polymerization Polymerization of ethylene was first carried out at 40°C for 10 min with the aim of finding the best Si(CH3)3OH/TiCI 4 mole ratio using ageing time of 10 min. The o b t a i n e d results are shown in Table 1, indicating that the catalytic activity is strongly dependent u p o n the Si/Ti ratio. The activity increases to reach a m a x i m u m value at Si/Ti = 2 a n d then decreases stressed at the employed conditions in this study. It was observed that the yellow colour o f TiC14 toluene solution change to a colourless solution after Si(CH3)3OH addition showing an evident reaction between these two reactants. The catalyst activity was also remarkably influenced by the ageing time (see Table 2) and the t e m p e r a t u r e of ageing. It was noted that the highest activity was reached a r o u n d 10 rain at r.t. A white solid was formed after 2 0 r a i n of ageing, indicating a change of the system nature becoming a n heterogeneous one. D e p e n d i n g on the c o n c e n t r a t i o n of reactants (Table 3), the catalyst Table 2. Results of ethylene polymerization by changing the ageing time of TiCI 4 and Si(CH3)3OH ~ Run Ageing time Temperature Yield No. (min) of ageing ('C) (g) 7 in site r.t. 0.87 8 l0 r.t. 2.25 9

10

0

1.44

10

30

r.t.

0.03

~Polymerization conditions are the same as those of run No. 4 except for the change in ageing time.

3. Effect of catalyst concentration on the activity of ethylene polymerization~ Run Concentration Yield No. mmol of Ti/ml (g) 11 0.002 3.12 12 0.001 1.49 13 0.0005 0.56 14 0.0003 n.r. aPolymerizationconditions are the same as those of run No. 4 except for the absolute concentration of Ti and Al(i-Bu)3 as cocatalyst.

Table

system shows to be very sensible to the dilution. It indicates that the interaction between TiCI4 a n d Si(CH3)aOH m i g h t be a c o o r d i n a t i o n nature a n d the formed complex is so weak. Table 4 shows the polymerization results o b t a i n e d with different kinds of alkylaluminum, suggesting that all trialkylalum i n u m s are available to activate the catalyst system. The use of Cl-containing alkylaluminum like AI(C2Hs)2C1 ( D E A C ) was not able to give a high catalytic activity. In addition, the m e t h y l a l u m i n o x a n e ( M A O ) was not also able to activate the catalyst system at the employed conditions in this study. Tables 5 a n d 6 show that the catalytic activity was very strongly affected by the AI/Ti mole ratio. F o r b o t h cocatalysts employed in this study, the activity increased quickly to reach a m a x i m u m value at AI(CH3)3/Ti a n d Al(i-Bu)3/Ti = 1 followed by a deep decrease with an increase in the a m o u n t of cocatalyst. Since this catalyst system is very unstable, we tried to s u p p o r t it over different types of carrier, such as SiO2 and MgC12 (see Table 7). The supported catalysts (run Nos 33 a n d 36) were able to polymerize ethylene even after 3 days, showing an increase in the stability of the catalyst system. Figures 1 a n d 2 show the non-modified a n d modified kinetic profiles of the catalyst, respectively. It can be seen that the modified catalyst presents a decay period after 1 0 m i n of polymerization. As it was seen in Table 2, the catalytic activity of the modified catalyst was strongly influenced by ageing time, thus it is possible that during the polymerization some active sites have been de-activated, causing the observed decay. The results shown in Table 8 indicate that the catalytic activity was remarkably affected by the type of cocatalyst a n d Si(CH3)3OH/CpTiCI 3 mole ratio. These results show that the catalytic activity increases up to the mole ratio o f Si/Ti = 1 followed by a gradual decrease with a n increase in the a m o u n t of Si(CH3)3OH. Table 8 shows that T I B A was the best cocatalyst for ethylene polymerization as it was also observed for TIC14 modified with TMS. Table 4. Results of ethylene polymerization with different kinds of alkylaluminums~ Run Yield m.p. No. Alkylaluminums (g) (C) 15 AI(CH3)3 2.25 132.8 16 AI(C2Hs)a 1.87 133.1 17 Al(i-Bu)3 3.12 133.9 18 AI(n-Ba)3 1.30 -19 AICI(C2H~)2 0.02 -20 MAOb trace -~Polymerizationconditions are the same as those of run No. 4 except for the change of alkylaluminums. bMAO = methylaluminoxane.

P o l y m e r i z a t i o n o f ethylene a n d p r o p y l e n e Table 5. Results of ethylene polymerization with different mole ratio of AI(CHs)s/TP Run No.

AI(CH~)3 (mmol)

21 22 23 24 25

AI/Ti mole ratio

Yield (g)

0 0.5 1.0 1.5 2.0

0 0.01 2.25 0.89 0.04

0 0.05 0. I 0.15 0.2

1297

lOOO OoOOo 800 A

.= I:-

600

"

400

o

o oo

o

o

o

$

~Polymerization conditions are the same as those of run No. 4 except for the amount of AI(CH03.

200

( Table 6. Results of ethylene polymerization with different mole ratio of AI(i-Bu)a/TP Run No.

Al(i-Bu)~ (mmol)

26 27 28 29 30 31 b

AI/Ti mole ratio

Yield (g)

0 0.5 1.0 I. 5 2.0 1.0

0 0.02 3.12 1.24 0.13 0.67

0 0.05 0.1 0.15 0.2 0.1

-20( -5

I

I

I

I

I

I

I

0

5

10

15

20

25

30

Time

( min )

35

Fig. 1. D e p e n d e n c e o f c a t a l y t i c activity o n the time o f p o l y m e r i z a t i o n f o r the n o n - m o d i f i e d c a t a l y s t .

5000

"Polymerization conditions are the same as those of run No. 4 except for the amount of Al(i-Bu)3. bPolymerization was conducted with the non-modified catalyst (Si/Ti = 0).

0

3800

0

0

0

0

0 0

A

0

260C

Table 7. The results of ethylene polymerization with different types of supported catalysP Run No. 32 33 b 34~ 35 36b

Catalyst system TiCI4/SiO 2 TiCI4/TMS/SiO 2 TiCI4/SiO2/TMS TiCI4/MgCI ~, TiCI4/TMS/MgCI 2

Yield (g)

m.p. ('C)

0.52 0.44 O. I 1 1.23 1.12

-119.2 -132.4 132.4

0 0

140C

20C

~TiCI4 (0.1 mmol) in toluene was added to the ground MgC12 or SiO 2 (treated at 90ff~C for 6 h r in vacuo), and used 1 g of carrier. The other polymerization conditions are the same as those of run No. 4. bPolymerization was conducted with the supported catalyst which was prepared by adding the modified TiCI 4 to SiO 2 or MgCI 2. ~Polymerization was conducted with the supported catalyst which was prepared by adding TiCI 4 to SiO 2 and treated with Si(CH03OH (TMS).

Table 8. Effect of the Si(CH 3)3OH/CpTiCI3 mole ratio on the activity of ethylene polymerization~ Run No.

-100C -5

I 0

I 5

i I 10 15 ~me(min)

I 20

i 25

i 30

35

Fig. 2. D e p e n d e n c e o f c a t a l y t i c activity o n the time o f p o l y m e r i z a t i o n for the m o d i f i e d c a t a l y s t .

Propylene polymerization Polymerization of propylene was conducted employing the best conditions for ethylene polymeriza t i o n , i.e. S i ( C H 3 ) a O H / T i C 1 4 = 2 and ageing time l0 rain. Table 9 shows the results of propylene polyme r i z a t i o n w i t h d i f f e r e n t k i n d s o f c o c a t a l y s t . It w a s o b s e r v e d t h a t t h e c a t a l y s t is e f f e c t i v e w h e n m o r e s t r o n g L e w i s a c i d is e m p l o y e d a s c o c a t a l y s t ( D E A C or MAO), showing an opposite trend of ethylene polymerization. The use of MAO was more effective

Si/Ti b mole/ratio

Alkylaluminums

Yield (g)

m.p. CC)

37 38 39 40 41

0 I 3 5 10

AI(CH3) ~ AI(CH3) 3 AI(CH3) 3 AI(CHs)3 AI(CH3) 3

0.08 0.82 0.78 0.40 0.11

133 134 ----

42 43

0 1

Al(i-Bu)~ Al(i-Bu)3

0.55 1.30

135 135

Run No.

44¢ 45 ~ 46~ 47~

0 I 5 I0

MAO ~ MAO MAO MAO

0.84 0.95 0.7 trace

-----

48

~Polymerization was conducted using 10 I mmol of CpTiCI 3, I mmol of cocatalyst, 25 cm 3 of toluene at 40"C for 16 hr at autoclave. bCpTiCl3 was treated with Si(CH03OH for 4 hr at r.t. in autoclave. cPolymerization was conducted using 10 ~mmol of CpTiCI3, 1 mmol of MAO, 50 cm 3 of toluene at 40"C for 15 rain at 1 atm. dMAO = methylaluminoxane.

m

Table 9. Results of propylene polymerization with different kinds of alkylaluminums~

49 50 51 52

Alkylaluminums --

AI(CH3 )3 Al(i-Bu)3 AICI(C~ H 5): MAO b

Yield (g)

1.15 (%)

0

--

0 0. I 0.7 1.56

-12 22 l0

=Polymerization was conducted using 10 ~mmol of TiCI4, 1 mmol of alkylaluminums, 30 cm 3 of toluene at 40'C for 4 hr with autoclave. bMAO = methylaluminoxane. cI.I. = isotactic index wt% of polymer insoluble in boiling heptane.

HYUN JOON KIM and LuIz CLAUDIODE SANTA MARIA

1298

Table 10. Results of propene polymerization with different mole ratio of AI/Ti' Run No.

Type of alkylaluminums

AI/Ti mole ratio

Yield (g)

I.I.c (%)

m.p. CC)

53 54

AI(CH3)3 AI(CH3)3

1 10

0 0

---

---

55 56 57

Al(i-Bu)~ Al(i-Bu)3 Ali(i-Bu)3

1 10 20

0 0.10 0.06

58 59 60 61

AICI(C2H5)2 AICI(C2H5)2 AICI(C2H 5)2 AICI(C2Hs)2

1 l0 20 30

trace 0.70 0.99 0.46

-22 25 28

--149.2 --

62 63 64 65 66

MAP MAP MAP MAP MAP

1 l0 20 30 50

trace 1.56 0.64 0.50 0.14

-l0 15 23 50

-148.7 ----

67b 68b

AICI(C2Hs)2 MAP

20 10

0.41 0.68

20 23

-149.1

m

_

_

D

_

_

m

~Polymerization was conducted like run No. 50 except for the change in alkylaluminums and AI/Ti mole ratio. bPolymerization was conducted with non-modified catalyst. q.l. = isotactic index wt% of polymer insoluble in boiling heptane. t h a n D E A C , indicating the influence o f Lewis acid p o w e r . A f u r t h e r s t u d y is n o w being carried o u t to predict the m e c h a n i s m m o r e precisely. T h e s e results will be r e p o r t e d in a n o t h e r p a p e r . T a b l e 10 s h o w s t h a t the AI/Ti m o l e ratio for p r o p y l e n e p o l y m e r i z a t i o n also h a s a r e m a r k a b l e influence o n the catalyst activity a n d stereospecificity. It w a s n o t e d t h a t the modified catalyst w a s m o r e active f o r p r o p y l e n e p o l y m e r i z a t i o n t h a n n o n modified o n e except for the use o f t r i i s o b u t y l a l u m i n u m a n d t r i m e t h y l a l u m i n u m . T h e increase in the A1/Ti m o d e ratio c a u s e d an increase in the stereospecificity o f the catalyst system. It can also be seen t h a t the catalyst activity decreased w h e n the A I / T i increased. P r o b a b l y the excess o f c o c a t a l y s t h a s des t r o y e d p a r t o f the catalytic c o m p l e x by the o v e r r e d u c t i o n o f t i t a n i u m . It w a s investigated the oxid a t i o n state o f t i t a n i u m by electron p a r a m a g n e t i c

r e s o n a n c e ( E P R ) analysis, c h a n g i n g the A I / T i m o l e ratio (A1/Ti = 0; 1 a n d 2 ) - - s e e Fig. 3. T h e modified catalyst w i t h o u t cocatalyst s h o w n n o c h a n g e in the E P R s p e c t r u m . O n the o t h e r h a n d , the catalyst treated w i t h T I B A at A1/Ti = 1 s h o w n the E P R signal with g - v a l u e s o f 1.93 a n d 1.96 w h i c h m a y be ascribed to p a r a m a g n e t i c n o n - a l k y l a t e d a n d alkylated Ti species, respectively. T h e increase in the AI/Ti m o l e ratio (A1/Ti = 2) p r o v o k e d the d i s a p p e a r a n c e o f b o t h signals a n d a n e w signal w i t h g - v a l u e o f 1.91 w a s observed. T h e results o f p r o p y l e n e p o l y m e r i z a t i o n u s i n g catalysts b a s e d o n CpTiC13 are s h o w n in T a b l e 11. T h e use o f T M S t u r n e d the catalyst m o r e effective w h e n M A P w a s e m p l o y e d as cocatalyst. I n fact, it w a s n o t e d t h a t the modified catalyst also catalysed the propylene polymerization when TIBA or T M A were used as cocatalyst. C o m p a r e d to the 13C-NMR

Table I I. Results of propylene polymerization with different catalyst systems~ Triad (%) Run No.

Catalyst system

69 70 71

CpTCI3 CpTiC13 CpTiC13

77 73 74 75b 76b 77c 78c 79d 80a

CpTiCI3/TMS CpTiCI3/TMS CpTiCI3/TMS CpTiCI3/SiP2 CpTiCI3/SIP2 CpTiCI3/SiO2 CpTiCI3/SiP2 CpTiCI~/TMS/SiO2 CpTiCI3/TMS/SiO2

Cocatalyst

Activity (kg PP/mole Ti)

[mm]

[mr]

[rr]

AI(CH3)3 Al(i-Bu)3 MAP

trace trace 5.5

----

----

----

AI(CH3) 3 Al(i-Bu)3 MAP

1.0 4.5 24.0

25 -20

44 -45

31 -35

AI(CH3)3 Al(i-Bu)3 AI(CH3)~ Al(i-Bu)3 AI(CH3)3 Al(i-Bu) 3

15.2 22.0 n.r. n.r. trace 2.1

ll 23 ---24

42 43 ---42

47 34 ---34

~Polymerization was conducted using 10-i mmol of CpTiCI3, 1 mmol of cocatalyst, 25 cm3of toluene at 40°C for 24 hr in autoclave. bPolymerization was conducted using 500 mg of supported catalyst (Ti content = l wt%), 0.2 mmol of cocatalyst, 25 cm3 of toluene at 40°C for 24 hr in autoclave. ~Polymerization conditions are the same to those of run No. 75 except for the change of aluminum contents which was 2 mmol. dPolymerization conditions are the same to those of run No. 75 except for using the catalyst which was prepared by adding the modified CpTiCI3 to SiP 2 (treated at 900"C for 6 hr under vacuo).

Polymerization of ethylene and propylene

that is, activity was improved by using a suitable amount of cocatalyst. It was not noted the same improvement in the catalytic activity when the modified CpTiCP 3 was supported on SiO2. More information is necessary to speculate the mechanism of catalyst modification with TMS. However, we would like to report here the preliminary results, expecting that they will be useful for the modification of titanocene catalysts.

a,

Receiver Gain=1000

1299

Receiver Gain=50

Fig. 3. EPR spectra of modified TiC14 with Si(CH3)3OH with different Al(i-Bu)3/Ti mole ratio. (a) AI/Ti = I; and (b) AI/Ti = 2, conditions for measurements see Experimental section.

Acknowledgements--We thank Conselho Nacional de Desenvolvimento Cienfifico e Tecnol6gico (Brazil) for its financial support to one of us. It is also a pleasure to acknowledge the stimulating discussions with Professor Kazuo Soga and coworkers. REFERENCES

spectrum of polypropylene obtained with modified CpTiC13/AI(CH3) 3 system (Run No. 72) and nonmodified CpTiCI3/SiO2/AI(CH3) 3 system (Run No. 75), there are some differences in the methyl triad region between two spectra. The [mm] value, which was only 11% at Run No. 75, but increased to 25% with the modified CpTiCI3/AI(Ch3) 3 catalyst system. The polymerization activity was closely connected with the amount of cocatalyst when the polymerization was carried out using CpTiC13/SiO 2 catalyst,

1. W. Kaminsky. In Transition Metal Catalyzed Polymerization (edited by R. P. Quirk, Ed.), p. 25. Harwood, New York (1983). 2. W. Kaminisky, M. Miri, H. Sinn and R. Woldt, Makromol. Chem., Rapid Commun. 4, 417 (1983). 3. R. F. Jordan, C. S. Bujgur, R. Willett and B. Scott. J. Am. chem. Soc. 108, 7410 (1986). 4. K. Soga, T. Shiono and H. J. Kim. Makromol. Chem. In press. 5. K. Soga, T. Shiono and H. J. Kim. Makromol. Chem., Rapid Commun. 15, 139 (1994).