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The influences of cocatalyst on propylene polymerization at high temperature with a MgCl2-supported TiCl4 catalyst system
PERGAMON
European Polymer Journal 35 (1999) 751±755
Short communication
The in¯uences of cocatalyst on propylene polymerization at high temperature with a MgCl2-supported TiCl4 catalyst system Shin-ichi Kojoh *, Mamoru Kioka, Norio Kashiwa Petrochemicals R & D Center, Mitsui Chemicals, Inc., 6-1-2 Waki, Waki-cho, Kuga-gun, Yamaguchi-ken 740, Japan Received 24 October 1997; accepted 8 April 1998
Abstract The in¯uences of alkylaluminum on propylene polymerizations at 1008C in the use of a MgCl2±TiCl4± aromaticdiester/alkylaluminum/alkoxysilane catalyst system were investigated. The activity with i-Bu3Al as alkylaluminum was higher than that with Et3Al, which was opposite to the results in the polymerizations at 708C. By the increase of alkylaluminum concentration, the activity was enhanced and the melting temperature of the obtained polymer remained unchanged in the polymerization with i-Bu3Al at 1008C. On the other hand, in the polymerization with Et3Al instead of i-Bu3Al, the activity was not enhanced and the melting temperature of the resulting polymer dropped by increasing the alkylaluminum concentration. They suggest that the eciency of forming the active sites in the polymerizations with i-Bu3Al is higher than that with Et3Al and the copolymerization of propylene with the monomer arising from alkylaluminum did not occur by the use of i-Bu3Al in the polymerization at 1008C. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction It is well known that a MgCl2-supported TiCl4 catalyst system containing aromaticdiester in combination with alkoxysilane and Et3Al exhibits high activity and stereospeci®city for propylene polymerization [1±6]. Therefore, it is the most popular catalyst system in the current commercial plants. Though this catalyst system is also superior to the older catalyst systems from the aspect of the stability of the catalyst performances at high temperature, both the activity and the stereospeci®city of it decrease as the polymerization temperature rises over 758C [4]. However, the polymerization at the higher temperature, such as 1008C, is desired industrially in order to reduce the burden of removing the heat of polymerization in the commercial plants.
* Corresponding author. Tel: +81 8275-3-9121; fax: +81 8275-3-8819; e-mail: [email protected].
In our previous paper [7], we reported that the activity of propylene polymerization with a MgCl2±TiCl4±dioctylphthalate (DOP)/Et3Al/diphenyldimethoxysilane (DPDMS) catalyst system at 1008C was extremely lower than the activity at 708C and the chain-transfer reaction by Et3Al occurred much faster than any other chain-transfer reactions at 1008C. Therefore, we think that the distinctive behavior of Et3Al at 1008C in the chain-transfer reaction would be related to the drastic drop of the activity at 1008C. In this paper, we will discuss the in¯uences of alkylaluminum on the results of the propylene polymerization at 1008C. 2. Experimental 2.1. Preparation of MgCl2-supported TiCl4 catalyst In a 800 ml stainless-steel pot containing 2.8 kg of stainless-steel balls (15 mm diameter), 20 g (0.21 mol)
0014-3057/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 8 ) 0 0 1 5 5 - 4
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S. Kojoh et al. / European Polymer Journal 35 (1999) 751±755
of MgCl2 were milled with 0.03 mol of DOP for 8 h under a nitrogen atmosphere. The milled MgCl2 was treated with 200 ml of TiCl4 at 808C for 2 h. Subsequently, the solid product was separated by ®ltration and washed twice with n-hexane.
with a refractive index detector, using a TSK mixed polystyrene gel column (G3000±G7000, exclusion limits 400,000,000 for polystyrene molecular weight) and o-dichlorobenzene as solvent at 1408C. The number-average and weight-average molecular weight (Mn and Mw, respectively) was calculated on the basis of a polystyrene standard calibration. The melting temperature (m.p.) was measured on a Perkin±Elmer DSC-7 dierential scanning calorimeter (DSC) in the following manner. First, the sample was heated to 2008C at 208C min ÿ 1, which is well above the m.p., and maintained at this temperature for 10 min. Then, it was cooled to 308C at 108C min ÿ 1 to crystallize, followed by reheating at 108C min ÿ 1. The thermogram of each sample was recorded in the second heating run in order to remove the thermal history. The instrument was calibrated by the melting points of indium and lead.
2.2. Propylene polymerization In a 1 l glass autoclave equipped with a stirrer, 500 ml of n-decane was added and the system was charged with propylene. Then, 6 mmol l ÿ 1 (mM) of triethylaluminum (Et3Al) or iso-butylaluminum (iBu3Al), 0.6 mM of DPDMS and 0.1 mM of the above catalyst (in terms of Ti) were added at polymerization temperature. Polymerization was carried out under atmospheric pressure at that temperature for 15 min or 1 h. During polymerization, 50 l h ÿ 1 of propylene was supplied continuously. After the polymerization time, a small amount of i-butanol was added to the autoclave to terminate polymerization, and then the whole product was poured into a large amount of methanol containing a small amount of hydrochloric acid. The obtained polypropylene (PP) was ®ltered and vacuumdried at 808C for 12 h.
3. Results and discussion First of all, the results of propylene polymerizations in the range of 50±1008C using a MgCl2±TiCl4±DOP/ i-Bu3Al/DPDMS catalyst system were compared with those using Et3Al [7] instead of i-Bu3Al (run nos. 1±3 and 5±7 in Table 1). In the polymerization with Et3Al, the drop of the activity at 1008C was remarkable. Both the decrease of Mn and the widening of Mw/Mn suggest the promotion of the chain-transfer reaction by Et3Al [7]. In the polymerization with i-Bu3Al, the drop in the activity at 1008C compared with the activity at 708C is smaller than that in the polymerization with Et3Al. Consequently, the activity with i-Bu3Al was higher than the activity with Et3Al in the polymerization at 1008C, which was opposite to the results at 708C. The Mn of the PP obtained with i-Bu3Al was higher and Mw/Mn of the PP with i-Bu3Al was narrower than those with Et3Al at any temperature. They suggest that
2.3. Polymer analyses 13
C NMR analysis was performed in the following manner. The polymer solution was prepared by dissolving 150 mg of the polymer sample at 1208C in a mixture of 0.5 ml of hexachlorobutadiene and 0.1 ml of perdeuteriobenzene. The 13C NMR spectrum was recorded on a JEOL GX-500 spectrometer operating at 125.8 MHz under proton noise decoupling in Fourier-transform mode. Instrumental conditions were as follows: pulse angle 458, pulse repetition 4.2 s, spectral width 7500 MHz, number of scans 20,000, temperature 1108C, data points 64 K. The molecular weight of PP was measured by a Millipore±Waters 150C gel permeation chromatograph (GPC) equipped
Table 1. The comparisons between the results with i-Bu3Al and Et3Al in propylene polymerization* Run no.
cocat.
Temp. (8C)
Al (mM)
Activity (g-PP/mmol-Ti h)
Mn
Mw/Mn
M.p. (8C)
1 2 3 4 5 6 7 8
i-Bu3Al i-Bu3Al i-Bu3Al i-Bu3Al Et3Al Et3Al Et3Al Et3Al
50 70 100 100 50 70 100 100
6 6 6 18 6 6 6 18
160 265 43 113 464 663 36 37
175,800 145,600 41,400 37,700 78,600 24,600 9900 6700
5.2 5.5 6.8 6.9 5.8 8.0 10.0 14.1
159.0 159.9 156.5 156.6 157.6 158.4 155.0 151.9
*Polymerization conditions: 50 lh ÿ 1 propylene under atmospheric pressure, 0.1 mM of Ti, 0.6 mM of DPDMS, 6 or 18 mM of iBu3Al or Et3Al in 0.5 l of n-decane, 1 h (run nos 3, 4, 7 and 8) or 15 min (run nos 1, 2, 5 and 6)
S. Kojoh et al. / European Polymer Journal 35 (1999) 751±755
the chain-transfer reaction by i-Bu3Al is slower than that by Et3Al. One of the probable interpretations of it is that the eciency of alkylaluminum as a chain-transfer regent depends on the sterical hindrance of itself. Namely, i-Bu3Al would be the less eective chaintransfer regent on account of its alkyl group's bulkiness. Next, in the polymerizations at 1008C, the in¯uences of the kind and the concentration of cocatalyst were
753
investigated and the results are shown in Table 1 as run nos. 4 and 8. The drop of Mn by the increase of the cocatalyst concentration was observed in both polymerizations with i-Bu3Al and Et3Al. The chain-transfer reactions in propylene polymerization at 1008C using Et3Al occurred mainly by Et3Al and the chaintransfer reaction by Et3Al would be promoted by the increase of the Et3Al concentration [7]. Therefore, the drop of Mn by the higher concentration of i-Bu3Al
Fig. 1. 13C-NMR spectra of the PPs prepared at 1008C with (a) i-Bu3Al or (b) Et3Al as cocatalyst. (The notations A1±A4 and B1± B4 are referred to in the lower part.)
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S. Kojoh et al. / European Polymer Journal 35 (1999) 751±755
Fig. 2. Schemes can form ag-CH2 and bb-CH2 in propylene polymerization.
would be due to the promotion of the chain-transfer reaction by i-Bu3Al as well as Et3Al, although the drop was mild in comparison with that using Et3Al probably because of its lower eciency as a chaintransfer reagent. By the increase of the cocatalyst concentration, the activity was enhanced only in the polymerization with i-Bu3Al. However, in the propylene polymerization using Et3Al, the activity at 708C was enhanced by increasing the Et3Al concentration [4] and Kashiwa et al. reported that the higher Et3Al concentration led to the increase of (C*) with a MgCl2±TiCl4±ethylbenzoate/Et3Al/ethylbenzoate catalyst system [8]. One of the provable explanations for no activity enhancement at 1008C by the higher Et3Al concentration in this report would be that the acceleration of the chain-transfer reaction by Et3Al leads to obstructing the performance of Et3Al as cocatalyst and failing somewhat to form the active sites. In fact, in the use of i-Bu3Al, which is an ineective chain-transfer reagent, the activity was enhanced in the polymerization at 1008C by the increase of the cocatalyst concentration. Table 1 shows that the remarkable drop of m.p. by increasing the cocatalyst concentration was observed only in the polymerization with Et3Al. All the PPs
polymerized at 1008C in Table 1 were measured by 13C NMR, but the PPs of run nos 4 and 8 did not give clear 13C NMR spectra due to the higher aluminum concentration in PPs. The 13C NMR spectra of the PPs of run nos 3 and 7 were shown in Fig. 1. Fig. 1 shows that some other peaks were observed in the PP with Et3Al (run no. 7) in addition to the peaks detected in the PP with i-Bu3Al (run no. 3). These additional peaks were assigned to chain-end groups, agCH2 and bb-CH2 as shown in Fig. 1. The observation of the chain-end groups is due to the lower molecular weight of the PP with Et3Al. The presence of ag-CH2 and bb-CH2 with a 2:1 ratio suggests that the PP with Et3Al contains the structure which is derived from the reaction shown in Fig. 2 as Scheme (a) the copolymerization of propylene with ethylene or Scheme (b) the 2,1-insertion of propylene accompanied by 1,3-insertion and 1,2-insertion. From these two proposed mechanisms, the latter is denied because the ab-CH2, which is indispensable for this scheme, was not observed in the 13C NMR spectrum shown in Fig. 1. Namely, the PP polymerized at 1008C with Et3Al would contain the isolated ethylene unit coming from the reaction of Scheme (a) in spite of no detection of ethylene in the fed gas and the gas phase in the reactor. In this polym-
S. Kojoh et al. / European Polymer Journal 35 (1999) 751±755
erization system, Et3Al is the only source for ethylene. Therefore, we believe that ethylene arising from Et3Al was consumed for the copolymerization with propylene. In fact, by increasing the concentration of Et3Al, the m.p. of the obtained PP dropped appreciably. It indicates that the increase of the amount of ethylene source leads to the higher frequent copolymerization of propylene with ethylene. Although i-Bu3Al may generate i-butylene by the decomposition of itself, the existence of the copolymerization of propylene with ibutylene was not observed at an appreciable level. It indicates that such copolymerization is dicult, if ibutylene exists with propylene. Eventually, the unexpected copolymerization did not occur in the propylene polymerization at 1008C by the use of i-Bu3Al. 4. Conclusion In the propylene polymerizations at 1008C using a MgCl2±TiCl4±DOP catalyst system in combination with alkylaluminum and DPDMS, the activity with iBu3Al as alkylaluminum was higher than that with Et3Al, which was opposite to the results at 708C. The increase of the i-Bu3Al concentration enhances the activity at 1008C, although the activity with Et3Al was not enhanced by the same operation. They indicate the dierence of the eciency to form the active sites between i-Bu3Al and Et3Al. It would be related to the
755
eciency as a chain-transfer reagent of alkylaluminum. Besides, the increase of the Et3Al concentration leads to the remarkable drop of m.p., which was not observed in the polymerization with i-Bu3Al. The 13C NMR data showed that the PP prepared with Et3Al was a random copolymer with a small amount of ethylene produced by the decomposition of Et3Al. The above suggests that i-Bu3Al would be a more suitable cocatalyst than Et3Al in the propylene polymerization at the higher temperature which is desired to reduce the burden of removing the heat of polymerization.
References [1] Parodi S, Nocci R, Giannini V, Barbe PC, Scata V. Eur. pat. 45977 to Montedison. S.P.A., 1981. [2] Ushida Y, Kashiwa N. Eur. pat. 86288 to Mitsui Petrochem. Inds. Ltd, 1983. [3] Soga K, Shiono T. Transition metal catalyzed polymerizations. Cambridge: Cambridge University Press, 1988. p. 266. [4] Spitz R, Bobichon C, Guyot A. Macromol Chem 1989;190:707. [5] Kioka M, Kashiwa N. J Mol Catal 1993;82:11. [6] Forte MC, Coutinho FMB. Eur Polym J 1996;32:605. [7] Kojoh S, Kioka M, Kashiwa N, Itoh M, Mizuno A. Polymer 1995;36:5015. [8] Kashiwa N, Yoshitake J. J Polym Bull 1984;11:479.
European Polymer Journal 35 (1999) 751±755
Short communication
The in¯uences of cocatalyst on propylene polymerization at high temperature with a MgCl2-supported TiCl4 catalyst system Shin-ichi Kojoh *, Mamoru Kioka, Norio Kashiwa Petrochemicals R & D Center, Mitsui Chemicals, Inc., 6-1-2 Waki, Waki-cho, Kuga-gun, Yamaguchi-ken 740, Japan Received 24 October 1997; accepted 8 April 1998
Abstract The in¯uences of alkylaluminum on propylene polymerizations at 1008C in the use of a MgCl2±TiCl4± aromaticdiester/alkylaluminum/alkoxysilane catalyst system were investigated. The activity with i-Bu3Al as alkylaluminum was higher than that with Et3Al, which was opposite to the results in the polymerizations at 708C. By the increase of alkylaluminum concentration, the activity was enhanced and the melting temperature of the obtained polymer remained unchanged in the polymerization with i-Bu3Al at 1008C. On the other hand, in the polymerization with Et3Al instead of i-Bu3Al, the activity was not enhanced and the melting temperature of the resulting polymer dropped by increasing the alkylaluminum concentration. They suggest that the eciency of forming the active sites in the polymerizations with i-Bu3Al is higher than that with Et3Al and the copolymerization of propylene with the monomer arising from alkylaluminum did not occur by the use of i-Bu3Al in the polymerization at 1008C. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction It is well known that a MgCl2-supported TiCl4 catalyst system containing aromaticdiester in combination with alkoxysilane and Et3Al exhibits high activity and stereospeci®city for propylene polymerization [1±6]. Therefore, it is the most popular catalyst system in the current commercial plants. Though this catalyst system is also superior to the older catalyst systems from the aspect of the stability of the catalyst performances at high temperature, both the activity and the stereospeci®city of it decrease as the polymerization temperature rises over 758C [4]. However, the polymerization at the higher temperature, such as 1008C, is desired industrially in order to reduce the burden of removing the heat of polymerization in the commercial plants.
* Corresponding author. Tel: +81 8275-3-9121; fax: +81 8275-3-8819; e-mail: [email protected].
In our previous paper [7], we reported that the activity of propylene polymerization with a MgCl2±TiCl4±dioctylphthalate (DOP)/Et3Al/diphenyldimethoxysilane (DPDMS) catalyst system at 1008C was extremely lower than the activity at 708C and the chain-transfer reaction by Et3Al occurred much faster than any other chain-transfer reactions at 1008C. Therefore, we think that the distinctive behavior of Et3Al at 1008C in the chain-transfer reaction would be related to the drastic drop of the activity at 1008C. In this paper, we will discuss the in¯uences of alkylaluminum on the results of the propylene polymerization at 1008C. 2. Experimental 2.1. Preparation of MgCl2-supported TiCl4 catalyst In a 800 ml stainless-steel pot containing 2.8 kg of stainless-steel balls (15 mm diameter), 20 g (0.21 mol)
0014-3057/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 8 ) 0 0 1 5 5 - 4
752
S. Kojoh et al. / European Polymer Journal 35 (1999) 751±755
of MgCl2 were milled with 0.03 mol of DOP for 8 h under a nitrogen atmosphere. The milled MgCl2 was treated with 200 ml of TiCl4 at 808C for 2 h. Subsequently, the solid product was separated by ®ltration and washed twice with n-hexane.
with a refractive index detector, using a TSK mixed polystyrene gel column (G3000±G7000, exclusion limits 400,000,000 for polystyrene molecular weight) and o-dichlorobenzene as solvent at 1408C. The number-average and weight-average molecular weight (Mn and Mw, respectively) was calculated on the basis of a polystyrene standard calibration. The melting temperature (m.p.) was measured on a Perkin±Elmer DSC-7 dierential scanning calorimeter (DSC) in the following manner. First, the sample was heated to 2008C at 208C min ÿ 1, which is well above the m.p., and maintained at this temperature for 10 min. Then, it was cooled to 308C at 108C min ÿ 1 to crystallize, followed by reheating at 108C min ÿ 1. The thermogram of each sample was recorded in the second heating run in order to remove the thermal history. The instrument was calibrated by the melting points of indium and lead.
2.2. Propylene polymerization In a 1 l glass autoclave equipped with a stirrer, 500 ml of n-decane was added and the system was charged with propylene. Then, 6 mmol l ÿ 1 (mM) of triethylaluminum (Et3Al) or iso-butylaluminum (iBu3Al), 0.6 mM of DPDMS and 0.1 mM of the above catalyst (in terms of Ti) were added at polymerization temperature. Polymerization was carried out under atmospheric pressure at that temperature for 15 min or 1 h. During polymerization, 50 l h ÿ 1 of propylene was supplied continuously. After the polymerization time, a small amount of i-butanol was added to the autoclave to terminate polymerization, and then the whole product was poured into a large amount of methanol containing a small amount of hydrochloric acid. The obtained polypropylene (PP) was ®ltered and vacuumdried at 808C for 12 h.
3. Results and discussion First of all, the results of propylene polymerizations in the range of 50±1008C using a MgCl2±TiCl4±DOP/ i-Bu3Al/DPDMS catalyst system were compared with those using Et3Al [7] instead of i-Bu3Al (run nos. 1±3 and 5±7 in Table 1). In the polymerization with Et3Al, the drop of the activity at 1008C was remarkable. Both the decrease of Mn and the widening of Mw/Mn suggest the promotion of the chain-transfer reaction by Et3Al [7]. In the polymerization with i-Bu3Al, the drop in the activity at 1008C compared with the activity at 708C is smaller than that in the polymerization with Et3Al. Consequently, the activity with i-Bu3Al was higher than the activity with Et3Al in the polymerization at 1008C, which was opposite to the results at 708C. The Mn of the PP obtained with i-Bu3Al was higher and Mw/Mn of the PP with i-Bu3Al was narrower than those with Et3Al at any temperature. They suggest that
2.3. Polymer analyses 13
C NMR analysis was performed in the following manner. The polymer solution was prepared by dissolving 150 mg of the polymer sample at 1208C in a mixture of 0.5 ml of hexachlorobutadiene and 0.1 ml of perdeuteriobenzene. The 13C NMR spectrum was recorded on a JEOL GX-500 spectrometer operating at 125.8 MHz under proton noise decoupling in Fourier-transform mode. Instrumental conditions were as follows: pulse angle 458, pulse repetition 4.2 s, spectral width 7500 MHz, number of scans 20,000, temperature 1108C, data points 64 K. The molecular weight of PP was measured by a Millipore±Waters 150C gel permeation chromatograph (GPC) equipped
Table 1. The comparisons between the results with i-Bu3Al and Et3Al in propylene polymerization* Run no.
cocat.
Temp. (8C)
Al (mM)
Activity (g-PP/mmol-Ti h)
Mn
Mw/Mn
M.p. (8C)
1 2 3 4 5 6 7 8
i-Bu3Al i-Bu3Al i-Bu3Al i-Bu3Al Et3Al Et3Al Et3Al Et3Al
50 70 100 100 50 70 100 100
6 6 6 18 6 6 6 18
160 265 43 113 464 663 36 37
175,800 145,600 41,400 37,700 78,600 24,600 9900 6700
5.2 5.5 6.8 6.9 5.8 8.0 10.0 14.1
159.0 159.9 156.5 156.6 157.6 158.4 155.0 151.9
*Polymerization conditions: 50 lh ÿ 1 propylene under atmospheric pressure, 0.1 mM of Ti, 0.6 mM of DPDMS, 6 or 18 mM of iBu3Al or Et3Al in 0.5 l of n-decane, 1 h (run nos 3, 4, 7 and 8) or 15 min (run nos 1, 2, 5 and 6)
S. Kojoh et al. / European Polymer Journal 35 (1999) 751±755
the chain-transfer reaction by i-Bu3Al is slower than that by Et3Al. One of the probable interpretations of it is that the eciency of alkylaluminum as a chain-transfer regent depends on the sterical hindrance of itself. Namely, i-Bu3Al would be the less eective chaintransfer regent on account of its alkyl group's bulkiness. Next, in the polymerizations at 1008C, the in¯uences of the kind and the concentration of cocatalyst were
753
investigated and the results are shown in Table 1 as run nos. 4 and 8. The drop of Mn by the increase of the cocatalyst concentration was observed in both polymerizations with i-Bu3Al and Et3Al. The chain-transfer reactions in propylene polymerization at 1008C using Et3Al occurred mainly by Et3Al and the chaintransfer reaction by Et3Al would be promoted by the increase of the Et3Al concentration [7]. Therefore, the drop of Mn by the higher concentration of i-Bu3Al
Fig. 1. 13C-NMR spectra of the PPs prepared at 1008C with (a) i-Bu3Al or (b) Et3Al as cocatalyst. (The notations A1±A4 and B1± B4 are referred to in the lower part.)
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S. Kojoh et al. / European Polymer Journal 35 (1999) 751±755
Fig. 2. Schemes can form ag-CH2 and bb-CH2 in propylene polymerization.
would be due to the promotion of the chain-transfer reaction by i-Bu3Al as well as Et3Al, although the drop was mild in comparison with that using Et3Al probably because of its lower eciency as a chaintransfer reagent. By the increase of the cocatalyst concentration, the activity was enhanced only in the polymerization with i-Bu3Al. However, in the propylene polymerization using Et3Al, the activity at 708C was enhanced by increasing the Et3Al concentration [4] and Kashiwa et al. reported that the higher Et3Al concentration led to the increase of (C*) with a MgCl2±TiCl4±ethylbenzoate/Et3Al/ethylbenzoate catalyst system [8]. One of the provable explanations for no activity enhancement at 1008C by the higher Et3Al concentration in this report would be that the acceleration of the chain-transfer reaction by Et3Al leads to obstructing the performance of Et3Al as cocatalyst and failing somewhat to form the active sites. In fact, in the use of i-Bu3Al, which is an ineective chain-transfer reagent, the activity was enhanced in the polymerization at 1008C by the increase of the cocatalyst concentration. Table 1 shows that the remarkable drop of m.p. by increasing the cocatalyst concentration was observed only in the polymerization with Et3Al. All the PPs
polymerized at 1008C in Table 1 were measured by 13C NMR, but the PPs of run nos 4 and 8 did not give clear 13C NMR spectra due to the higher aluminum concentration in PPs. The 13C NMR spectra of the PPs of run nos 3 and 7 were shown in Fig. 1. Fig. 1 shows that some other peaks were observed in the PP with Et3Al (run no. 7) in addition to the peaks detected in the PP with i-Bu3Al (run no. 3). These additional peaks were assigned to chain-end groups, agCH2 and bb-CH2 as shown in Fig. 1. The observation of the chain-end groups is due to the lower molecular weight of the PP with Et3Al. The presence of ag-CH2 and bb-CH2 with a 2:1 ratio suggests that the PP with Et3Al contains the structure which is derived from the reaction shown in Fig. 2 as Scheme (a) the copolymerization of propylene with ethylene or Scheme (b) the 2,1-insertion of propylene accompanied by 1,3-insertion and 1,2-insertion. From these two proposed mechanisms, the latter is denied because the ab-CH2, which is indispensable for this scheme, was not observed in the 13C NMR spectrum shown in Fig. 1. Namely, the PP polymerized at 1008C with Et3Al would contain the isolated ethylene unit coming from the reaction of Scheme (a) in spite of no detection of ethylene in the fed gas and the gas phase in the reactor. In this polym-
S. Kojoh et al. / European Polymer Journal 35 (1999) 751±755
erization system, Et3Al is the only source for ethylene. Therefore, we believe that ethylene arising from Et3Al was consumed for the copolymerization with propylene. In fact, by increasing the concentration of Et3Al, the m.p. of the obtained PP dropped appreciably. It indicates that the increase of the amount of ethylene source leads to the higher frequent copolymerization of propylene with ethylene. Although i-Bu3Al may generate i-butylene by the decomposition of itself, the existence of the copolymerization of propylene with ibutylene was not observed at an appreciable level. It indicates that such copolymerization is dicult, if ibutylene exists with propylene. Eventually, the unexpected copolymerization did not occur in the propylene polymerization at 1008C by the use of i-Bu3Al. 4. Conclusion In the propylene polymerizations at 1008C using a MgCl2±TiCl4±DOP catalyst system in combination with alkylaluminum and DPDMS, the activity with iBu3Al as alkylaluminum was higher than that with Et3Al, which was opposite to the results at 708C. The increase of the i-Bu3Al concentration enhances the activity at 1008C, although the activity with Et3Al was not enhanced by the same operation. They indicate the dierence of the eciency to form the active sites between i-Bu3Al and Et3Al. It would be related to the
755
eciency as a chain-transfer reagent of alkylaluminum. Besides, the increase of the Et3Al concentration leads to the remarkable drop of m.p., which was not observed in the polymerization with i-Bu3Al. The 13C NMR data showed that the PP prepared with Et3Al was a random copolymer with a small amount of ethylene produced by the decomposition of Et3Al. The above suggests that i-Bu3Al would be a more suitable cocatalyst than Et3Al in the propylene polymerization at the higher temperature which is desired to reduce the burden of removing the heat of polymerization.
References [1] Parodi S, Nocci R, Giannini V, Barbe PC, Scata V. Eur. pat. 45977 to Montedison. S.P.A., 1981. [2] Ushida Y, Kashiwa N. Eur. pat. 86288 to Mitsui Petrochem. Inds. Ltd, 1983. [3] Soga K, Shiono T. Transition metal catalyzed polymerizations. Cambridge: Cambridge University Press, 1988. p. 266. [4] Spitz R, Bobichon C, Guyot A. Macromol Chem 1989;190:707. [5] Kioka M, Kashiwa N. J Mol Catal 1993;82:11. [6] Forte MC, Coutinho FMB. Eur Polym J 1996;32:605. [7] Kojoh S, Kioka M, Kashiwa N, Itoh M, Mizuno A. Polymer 1995;36:5015. [8] Kashiwa N, Yoshitake J. J Polym Bull 1984;11:479.