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Effects of Temperature in Syndiospecific Living Polymerization of Propylene with [t-BuNSiMe2(3,6-t-Bu2Flu)]TiMe2-MMAO Catalyst
Progress in Olefin Polymerization Catalysts and Polyolefin Polyolefin Materials T. Shiono, K. Nomura and M. Terano (Editors) © 2006 Elsevier B.V. All rights reserved.
189
30
Effects of Temperature in Syndiospecific Living Polymerization of Propylene with [^-BuNSiMe2(3,6*-Bu2Flu)]TiMe2-MMAO Catalyst Zhengguo Cai, Nakayama Yuushou, Takeshi SMono* Graduate School of Engineering, Hiroshima University, Kagamiyama I-4-l, HigashiHiroshima 739-8527, Japan
Abstract Propylene polymerizations were conducted by [/-BuNSiMe2(3,6~£Bu2Flu)]TiMea using trialkylaluminum-free modified niethylaluminoxane as a cocatalyst in toluene at -20, 0 and 25 °C. The raise of polymerization temperature improved the activity to produce 2400 kg of polymer per mole of Ti per hour at 25 °C, and the post-polymerization testified that the propylene polymerization proceeded in a living manner regardless of the polymerization temperature. The polymerization temperature also influenced the stereoregularity of the polypropylenes (PP). The system gave syndiotactic crystalline PP at -20 °C with a melting point of 129 °C and amorphous PP at 25 °C, respectively. 1. INTRODUCTION Single-site catalysts based on group 4 metallocene complexes have been investigated for the development of new olefin polymerization catalysis [1,2]. Intense effort has been paid to elucidate the effects of polymerization conditions (cocatalyst, monomer concentration, solvent, temperature, etc.) on the polymerization behaviour. Polymerization temperature is one of the most important factors that largely influence the activity and the stereospecificity. We have previously reported that [r-BuNSiMe2(3,6-£-Bu2Flu)]TiMe2 (1) activated by trialkylaluminum-free modified methylaluminoxane (dMMAO) conducted highly syndiospecific living polymerization of propylene in heptane at 0 °C[3].
190
Z.Caietal
In the present work, we investigated the effects of polymerization temperature on the syndiospecificity of the present catalyst in toluene. 2. EXPERIMENTAL Materials. All operations were performed under argon gas using standard Schlenk techniques and all solvents were dried by usual procedures and freshly distilled before use. The complex 1 and dMMAO were prepared according to the procedures reported previously[3,4]. Research grade propylene (Takachiho Chemicals Co.) was purified by passing it through columns of NaOH, PaOj, and molecular sieves 3 A, followed by bubbling it through a NaAlH2Et2/l,2,3,4,tetrahydronaphthalene solution. Polymerization Procedure. Polymerization was performed in a 100 mL glass reactor equipped with a magnetic stirrer and carried out by the following methods. After a certain amount of dMMAO solution in toluene had been saturated with an atmospheric pressure of propylene, polymerization was started by the addition of 1 mL solution of 1. Polymerization was conducted for a certain time and terminated with acidic methanol. The polymers obtained were adequately washed with methanol and dried under vacuum at 60 °C for 6 h. Analytical Procedures. Molecular weight and molecular weight distribution of polymer obtained were determined by gel permeation chromatography with a Waters 150 CV at 140 °C using o-dichlorobenzene as a solvent. The parameters for universal calibration were K = 7.36 x 10"s, a- 0.75 for polystyrene standard and K = 1.03 x 10"4, cr = 0.78 for PP samples. The 13C NMR spectra of PPs were measured at 130 °C on a JEOL JNM-400 spectrometer operated at 400 MHz in the pulse Fourier-Transform mode. The pulse angle was 45° and about 10 000 scans were accumulated in pulse repetition of 5.0 s. Sample solutions were prepared in I,l,2,2-tetrachloroethane-d2 and the central peak of the solvent (74.47 ppm) was used as an internal reference. Differential scanning calorimetry (DSC) analyses were performed on a Seiko DSC-220 and the DSC curves of the samples were recorded under a nitrogen atmosphere with a heating rate of 10 °C/min from 20-200 °C. 3. RESULTS AND DISCUSSION 3,1. Propylene polymerization at various temperatures Propylene polymerizations were conducted with 1-dMMAO in toluene at -20 °C, 0 and 25 °C by a semi-batch method. Polymerization was quenched before the produced polymer would interrupt effective stirring according to the
JO. Effects of Temperature on Living Polymerization ofPropylene
191
polymerization temperature. The results are summarized in Table 1. The catalytic system gave the polymers with comparatively narrow molecularweight distribution (MWD) regardless of the polymerization temperatures. The raise of polymerization temperature enhanced the activity but did not affect the number of polymer chains (N), which was about 60 - 65 % of the Ti used. These results suggest that the catalytic system should conduct living polymerization of propylene. To investigate the living nature of 1-dMMAO at these temperatures, we conducted post-polymerization by a batch method. The results of the post-polymerization indicate that the propylene polymerization proceeded in a living manner in toluene at -20, 0 and 25 °C. Table 1 Results ofPropylene Polymerization with 1-dMMAO entry
temp.
time
yield
activity h
Mn c
MJMn* 4
(xlO )
Nd
rf
T
r
fC)
(°C)
(min)
(g)
Qimol)
1
-20
8
0.76
285
6.5
1.35
12
0.90
129
2
0
4
2.36
1768
18.8
1.36
13
0.83
100
3
20
3
2.42
2420
17.9
1.32
13
0.60
a
Polymerization conditions: toluene = 30 mL, Ti = 20 junol, Al = 4.0 mmol, propylene =1,0 atm. Activity in kg-PP/(mol~Ti»h). c Number average molecular weight and molecular weight distribution determined by GPC using universal calibration. d Calculated from yield and Mn. e Determined by I3C NMR. f Melting temperature determined by DSC. BNot detected. b
3.2. Structures of Polypropylene® obtained at various temperatures The steric pentad distributions were determined from the resonances of methyl carbons in 13C NMR spectra, and the results are shown in Table 2. The PP obtained at -20 °C showed the highest syndiotactic pentad value (rrrr) of 0,90, which decreased according to the raise of polymerization temperature to 0.83 at 0 °C and 0.60 at 25 °C. Consequently the PP obtained at -20 °C was crystalline polymer with melting point of 129 °C, whereas that obtained at 25 °C was amorphous one. In the enantiomorphic-site controlled syndiospecific polymerization with a Cs symmetric catalyst, two types of stereodefects should be formed: one is "rmrr" arising from the "chain migration" without monomer insertion and the other is "rmmr" arising from the "monomer miss-insertion" [5]. Table 2 indicates that rmrr content was increased by the raising polymerization temperature, -20 °C (0.02) < 0 °C (0.10) < 25 °C (0.23), whereas the rmmr content was almost constant and slightly increased only at 25 °C, -20 °C (0.02) = 0 °C (0.02) < 25 °C (0.04). These results imply that the decrease of the syndiospecificity caused
192
ZCaietal
by raising the temperature is mainly attributed to the frequent "chain migration". The similar phenomena were observed in the syndiospecific propylene polymerization with Cs-symmetric zirconocene catalysts[6-8]. Table 2 Stene Pentad Distributions of Polypropylenes Obtained at Various Temperatures entry (temp)
Steric pentad content mmmfli
mmmr
rmmr
mnirr
TO
rmrr +
nnrni
rrrr
mrrr
mrrm
mmrm
1 (-20)
0.00
0.00
0.02
0.05
0.02
0.01
0.83
0,07
0.00
2(0)
0.00
0.00
0.02
0.04
0.10
0.01
0.70
0.13
0.00
3(25)
0.00
0.01
0.04
0.09
0.23
0.06
0.39
0.20
0.01
"Determined by 13C NMR.
4. CONCLUSIONS The effects of polymerization temperature were investigated in propylene polymerization by 1-dMMAO in toluene under an atmospheric pressure of propylene. The activity increased by raising the temperature from -20 °C to 25 °C with keeping living polymerization accompanied by the decrease of the syndiospecifieity. The system gave syndiotactic crystalline PP with a melting point of 129 °C at -20 °C and amorphous PP at 25 °C. Acknowledgements This work was supported by the New Energy and Development Organization (NEDO) for the Project on Nanostructured Polymeric Materials. We thank Tosoh-Finechem Co. for donating MAO. References [1] W. Kaminsky, Advances in Catalysis 46 (2001) S9-159. [2] V. C. Gibson, S. K. Spitzmesser, Chem. Rev. 103 (2003) 283-315. [3] Z. Cai, T. Ikeda, M. Akita, T. Shiono, Macromolecules 38 (2005) 8135-8139. [4] H. Hagimoto, T. Shiono, T. Ikeda, Macromol. Rapid. Common. 23 (2002) 73-76. [5] J. A. Ewen, M. J. Elder, R. L. Jones, L. Haspeslagh, J. L. Atwood, S. G. Bott, and K. Robinson, Makromol, Chem., Macromol. Symp. 48/49 (1991) 253-295. [6] J. A. Ewen, M. J. Elder, R. L. Jones, S. Curtis, H. N. Cheng, Stud. Surf. Sci. Caial. 56 (1990) 439-412. [7] D. Veghini, L. M. Henling, T. J. Burkhardt, J. E. Bercaw, J. Am. Chem. Soc. 121 (1999) 564573. [8] M.-C. Chen, T. J. Marks, J. Am. Chem. Soc. 123 (2001) 11803-11804.
189
30
Effects of Temperature in Syndiospecific Living Polymerization of Propylene with [^-BuNSiMe2(3,6*-Bu2Flu)]TiMe2-MMAO Catalyst Zhengguo Cai, Nakayama Yuushou, Takeshi SMono* Graduate School of Engineering, Hiroshima University, Kagamiyama I-4-l, HigashiHiroshima 739-8527, Japan
Abstract Propylene polymerizations were conducted by [/-BuNSiMe2(3,6~£Bu2Flu)]TiMea using trialkylaluminum-free modified niethylaluminoxane as a cocatalyst in toluene at -20, 0 and 25 °C. The raise of polymerization temperature improved the activity to produce 2400 kg of polymer per mole of Ti per hour at 25 °C, and the post-polymerization testified that the propylene polymerization proceeded in a living manner regardless of the polymerization temperature. The polymerization temperature also influenced the stereoregularity of the polypropylenes (PP). The system gave syndiotactic crystalline PP at -20 °C with a melting point of 129 °C and amorphous PP at 25 °C, respectively. 1. INTRODUCTION Single-site catalysts based on group 4 metallocene complexes have been investigated for the development of new olefin polymerization catalysis [1,2]. Intense effort has been paid to elucidate the effects of polymerization conditions (cocatalyst, monomer concentration, solvent, temperature, etc.) on the polymerization behaviour. Polymerization temperature is one of the most important factors that largely influence the activity and the stereospecificity. We have previously reported that [r-BuNSiMe2(3,6-£-Bu2Flu)]TiMe2 (1) activated by trialkylaluminum-free modified methylaluminoxane (dMMAO) conducted highly syndiospecific living polymerization of propylene in heptane at 0 °C[3].
190
Z.Caietal
In the present work, we investigated the effects of polymerization temperature on the syndiospecificity of the present catalyst in toluene. 2. EXPERIMENTAL Materials. All operations were performed under argon gas using standard Schlenk techniques and all solvents were dried by usual procedures and freshly distilled before use. The complex 1 and dMMAO were prepared according to the procedures reported previously[3,4]. Research grade propylene (Takachiho Chemicals Co.) was purified by passing it through columns of NaOH, PaOj, and molecular sieves 3 A, followed by bubbling it through a NaAlH2Et2/l,2,3,4,tetrahydronaphthalene solution. Polymerization Procedure. Polymerization was performed in a 100 mL glass reactor equipped with a magnetic stirrer and carried out by the following methods. After a certain amount of dMMAO solution in toluene had been saturated with an atmospheric pressure of propylene, polymerization was started by the addition of 1 mL solution of 1. Polymerization was conducted for a certain time and terminated with acidic methanol. The polymers obtained were adequately washed with methanol and dried under vacuum at 60 °C for 6 h. Analytical Procedures. Molecular weight and molecular weight distribution of polymer obtained were determined by gel permeation chromatography with a Waters 150 CV at 140 °C using o-dichlorobenzene as a solvent. The parameters for universal calibration were K = 7.36 x 10"s, a- 0.75 for polystyrene standard and K = 1.03 x 10"4, cr = 0.78 for PP samples. The 13C NMR spectra of PPs were measured at 130 °C on a JEOL JNM-400 spectrometer operated at 400 MHz in the pulse Fourier-Transform mode. The pulse angle was 45° and about 10 000 scans were accumulated in pulse repetition of 5.0 s. Sample solutions were prepared in I,l,2,2-tetrachloroethane-d2 and the central peak of the solvent (74.47 ppm) was used as an internal reference. Differential scanning calorimetry (DSC) analyses were performed on a Seiko DSC-220 and the DSC curves of the samples were recorded under a nitrogen atmosphere with a heating rate of 10 °C/min from 20-200 °C. 3. RESULTS AND DISCUSSION 3,1. Propylene polymerization at various temperatures Propylene polymerizations were conducted with 1-dMMAO in toluene at -20 °C, 0 and 25 °C by a semi-batch method. Polymerization was quenched before the produced polymer would interrupt effective stirring according to the
JO. Effects of Temperature on Living Polymerization ofPropylene
191
polymerization temperature. The results are summarized in Table 1. The catalytic system gave the polymers with comparatively narrow molecularweight distribution (MWD) regardless of the polymerization temperatures. The raise of polymerization temperature enhanced the activity but did not affect the number of polymer chains (N), which was about 60 - 65 % of the Ti used. These results suggest that the catalytic system should conduct living polymerization of propylene. To investigate the living nature of 1-dMMAO at these temperatures, we conducted post-polymerization by a batch method. The results of the post-polymerization indicate that the propylene polymerization proceeded in a living manner in toluene at -20, 0 and 25 °C. Table 1 Results ofPropylene Polymerization with 1-dMMAO entry
temp.
time
yield
activity h
Mn c
MJMn* 4
(xlO )
Nd
rf
T
r
fC)
(°C)
(min)
(g)
Qimol)
1
-20
8
0.76
285
6.5
1.35
12
0.90
129
2
0
4
2.36
1768
18.8
1.36
13
0.83
100
3
20
3
2.42
2420
17.9
1.32
13
0.60
a
Polymerization conditions: toluene = 30 mL, Ti = 20 junol, Al = 4.0 mmol, propylene =1,0 atm. Activity in kg-PP/(mol~Ti»h). c Number average molecular weight and molecular weight distribution determined by GPC using universal calibration. d Calculated from yield and Mn. e Determined by I3C NMR. f Melting temperature determined by DSC. BNot detected. b
3.2. Structures of Polypropylene® obtained at various temperatures The steric pentad distributions were determined from the resonances of methyl carbons in 13C NMR spectra, and the results are shown in Table 2. The PP obtained at -20 °C showed the highest syndiotactic pentad value (rrrr) of 0,90, which decreased according to the raise of polymerization temperature to 0.83 at 0 °C and 0.60 at 25 °C. Consequently the PP obtained at -20 °C was crystalline polymer with melting point of 129 °C, whereas that obtained at 25 °C was amorphous one. In the enantiomorphic-site controlled syndiospecific polymerization with a Cs symmetric catalyst, two types of stereodefects should be formed: one is "rmrr" arising from the "chain migration" without monomer insertion and the other is "rmmr" arising from the "monomer miss-insertion" [5]. Table 2 indicates that rmrr content was increased by the raising polymerization temperature, -20 °C (0.02) < 0 °C (0.10) < 25 °C (0.23), whereas the rmmr content was almost constant and slightly increased only at 25 °C, -20 °C (0.02) = 0 °C (0.02) < 25 °C (0.04). These results imply that the decrease of the syndiospecificity caused
192
ZCaietal
by raising the temperature is mainly attributed to the frequent "chain migration". The similar phenomena were observed in the syndiospecific propylene polymerization with Cs-symmetric zirconocene catalysts[6-8]. Table 2 Stene Pentad Distributions of Polypropylenes Obtained at Various Temperatures entry (temp)
Steric pentad content mmmfli
mmmr
rmmr
mnirr
TO
rmrr +
nnrni
rrrr
mrrr
mrrm
mmrm
1 (-20)
0.00
0.00
0.02
0.05
0.02
0.01
0.83
0,07
0.00
2(0)
0.00
0.00
0.02
0.04
0.10
0.01
0.70
0.13
0.00
3(25)
0.00
0.01
0.04
0.09
0.23
0.06
0.39
0.20
0.01
"Determined by 13C NMR.
4. CONCLUSIONS The effects of polymerization temperature were investigated in propylene polymerization by 1-dMMAO in toluene under an atmospheric pressure of propylene. The activity increased by raising the temperature from -20 °C to 25 °C with keeping living polymerization accompanied by the decrease of the syndiospecifieity. The system gave syndiotactic crystalline PP with a melting point of 129 °C at -20 °C and amorphous PP at 25 °C. Acknowledgements This work was supported by the New Energy and Development Organization (NEDO) for the Project on Nanostructured Polymeric Materials. We thank Tosoh-Finechem Co. for donating MAO. References [1] W. Kaminsky, Advances in Catalysis 46 (2001) S9-159. [2] V. C. Gibson, S. K. Spitzmesser, Chem. Rev. 103 (2003) 283-315. [3] Z. Cai, T. Ikeda, M. Akita, T. Shiono, Macromolecules 38 (2005) 8135-8139. [4] H. Hagimoto, T. Shiono, T. Ikeda, Macromol. Rapid. Common. 23 (2002) 73-76. [5] J. A. Ewen, M. J. Elder, R. L. Jones, L. Haspeslagh, J. L. Atwood, S. G. Bott, and K. Robinson, Makromol, Chem., Macromol. Symp. 48/49 (1991) 253-295. [6] J. A. Ewen, M. J. Elder, R. L. Jones, S. Curtis, H. N. Cheng, Stud. Surf. Sci. Caial. 56 (1990) 439-412. [7] D. Veghini, L. M. Henling, T. J. Burkhardt, J. E. Bercaw, J. Am. Chem. Soc. 121 (1999) 564573. [8] M.-C. Chen, T. J. Marks, J. Am. Chem. Soc. 123 (2001) 11803-11804.