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Additive Effects of Dialkylaluminum Hydrides on Propylene-1,3-Butadiene Copolymerization Using an Isospecific Zirconocene 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.
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Additive Effects of Dialkylaluminum Hydrides on Propylene~l,3-Butadiene Copolymerization Using an Isospecific Zirconocene Catalyst Takeshi Ishihara,a Hoang The Ban,a Hideaki Hagihara,b Takeshi Shionoc a
Japan Chemical Innovation Institute, AIST Tsukuba, Central 5-8, 1-1-1 Higashi, Tsukuba, Iharaki 305-8565, Japan b National Institute of Advanced Industrial Science and Technology, Tsukuba, Central 5-8, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan e Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
Abstract Additive effects of dialkylaluminum hydrides on propylene-l,3-butadiene copolymerization were investigated with an isospecific zirconocene catalyst, rac-dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride (4Ph), activated by modified methylaluminoxane. Dialkylaluminum hydrides improved the apparent selectivity for 1,2-insertion of 1,3-butadiene to give a pendant vinyl group. 13C NMR analysis of the eopolymers indicated that the dialkylaluminum hydride converted the 1,4-inserted butadiene unit in the copolymer to tetramethylene unit after methanolysis. 1. INTRODUCTION Polypropylene (PP) has been expanding its usage due to its mechanical balance and economical advantage. PP is, however, so hydrophobic that many attempts have been made to improve affinity of PP with other polar materials [1-2]. We have been developing copolymerization techniques to control the amount and location of polar groups in PP chain and succeeded in the selective introduction of carbon-carbon double bond as a precursor of polar group by the copolymerization of propylene and 1,3-butadiene using isospecific zirconocene
198
T. Ishihara et al,
catalysts [3-4]. The addition of hydrogen was found to hydrogenise the 1,4inserted butadiene units (1,4-BD) in the copolymer, and selectively produced PP with pendant vinyl groups. In this paper, therefore, we investigated the additive effects of dialkylaluminum hydrides on the copolymerization whether the dialkylaluminum hydrides react with 1,4-BD to produce PP having dialkylaluminum group on the main chain of the copolymer or not. 2. EXPERIMENTAL Materials. 4Ph commercially obtained from Boulder Scientific Company, and modified methylaluminoxane (MMAO) and other aluminum compounds purchased from Tosoh-Finechem. Co., were used without further purification. Other chemicals commercially obtained were purified according to the usual procedures. Polymerization procedure, Copolymerization of propylene with 1,3-butadiene was conducted in a 100-mL stainless steel autoclave by batch-wise operation at 0°C. Analytical procedures, 'H TSTMR and I3C TSTMR spectra were obtained in 1,1,2,2tetrachloroethane-d2 at 120 °C on a JEOL JNM-LA600 spectrometer. Molecular weights and molecular weight distributions of the copolymers were determined by a PL-GPC210 at 140 °C using o-dichlorobenzene as a solvent. 3. RESULTS AND DISCUSSION 3.1. Results of copolymerization The results of propylene-l,3-butadiene copolymerization using 4Ph-MMAO system are summarized in Table 1.
the
Table 1. Additive effects of aluminum compounds on propylene— 1,3-butadiene copolymerization*
additive
Yield (B)
Rsp (kgpolymer / mol-Zr»h) 13.1 15.8 35.8
(xlO3)
MJ Mnb
Mole fraction6 (%) 1,21,4H-1,4 BD BD -BD 1.43 0.76 0 0.23 1.26 0.63 0.26 0.4S 1.59
Selectivity {%) i *} nn
nan 0.08 2.4 35.7 65.3 0.1 34.2 84.6 DEAL-H 1.6 0.21 13.0 3.9 85.9 DiBAL-H "Polymerization conditions: solvent (toluene) = 40 mL, 4Ph = 2 jimol, MMAO = 4.0 mmol, 0 °C, 3 h, propylene concentration 1.8 mol / L, butadiene concentration 90 mmol / L. bNumber average molecular weight and molecular weight distribution determined by GPC using universal calibration.e Calculated from 'H and 13C NMR spectra. A Selectivities were the relative ratios of 1, 2—BD mole fractions to all double bonds.
32. Additive Effects ofDiatkylatuminum Hydrides
199
Dialkylaluminum hydrides, i.e., diethylaluminum hydride (DEAL-H) and diisobutylaluminum hydride (DiBAL—H), increased polymerization activities. The addition of DEAL-H did not affect the molecular weight (Mn) of the copolymer, whereas the introduction of DiBAL—H decreased the Ma value. An increase in polymerization activity accompanied by a decrease of molecular weight indicates that DiBAL-H caused chain transfer reaction. 3.2. Structures of copolymers The addition of the dialkylaluminum hydrides caused the decrease of 1,4—BD in the copolymer as observed in the *H NMR spectra (Fig. 1). The selectivity for 1, 2-BD in copolymers determined by 'H NMR are shown in Table 1.
I III-AI -II
Fig.l H NMR spectra of propylene- 1, 3- butadiene capolymer with and without DiBAL-H
[I'M
Fig, 2 " C NMR spectra of propylene-1, 3butadiene eopolymers synthesized with and without DiBAL-H.
The selectivity was improved from 65 to 85 % by the addition of the dialkylaluminum hydrides. To investigate the structures of copolymers in more details, we measured the 13C NMR spectra of copolymers obtained with and without DiBAL-H (Fig. 2). The signals assignable to pendant vinyl group and those to 1,4-BD structure were observed in both samples. The addition of DiBAL-H, however, caused the emergence of new signals derived from hydrogenated 1,4-BD (H-1,4-BD). The total mole fractions of 1,4-BD and H-1,4-BD were unchanged by the addition of the dialkylaluminum hydrides
200
T. Ishihara ct al.
(Table 1). The results indicate that the dialkylaluminum hydrides did not affect the mode of butadiene insertion but hydroaluminated the 1,4-BD units. A plausible copolymerization mechanism is shown in Scheme 1. Dialkylaluminum hydride and propylene competitively react with 7t-allyl Zr complex formed by 1,4-insertion of butadiene (A in Scheme 1). Insertion of propylene to A forms 1,4-BD in main chain (C), When dialkylalunium hydride reacts with A, hydroaluminated 1,4-BD is formed (B, D), which could incorporate successive propylene insertion more smoothly. The hydroaluminated 1,4-BD gives H—1,4—BD in main chain after methanolysis (E). Scheme 1 Reaction scheme &rpropylene-l,3-butadiene copolymerization with zirconocene— MMAO-dialkylaluminum hydride
4. CONCLUSIONS The 4Ph-MMAO-dialkylaluminum hydride system produced PP copolymer with pendant vinyl group. Although their selectivity of reduction from 1,4-BD to H—1,4—BD was lower than that with hydrogen [4], the copolymer possessed dialkylaluminum groups in main chain which can be utilized for functionalization of PP. Acknowledgements This work was supported by the New Energy and Development Organization (NEDO) through a grant for "Project on Nanostructured Polymeric Materials" under the Nanotechnology Program. References [1] T. C. Chung, Prog. Polym. Sci. 27 (2002) 39-85. [2] G. Moad, Prog. Polym. Sci. 24 (1999) 81-142. [3] T. Ishihara and T. Shiono, Macromolecules 36 (2003) 9675-9677. [4] T. Ishihara and T. Shiono, J. Am. Chem. Soc. 127 (2005) 5774-5775.
197
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Additive Effects of Dialkylaluminum Hydrides on Propylene~l,3-Butadiene Copolymerization Using an Isospecific Zirconocene Catalyst Takeshi Ishihara,a Hoang The Ban,a Hideaki Hagihara,b Takeshi Shionoc a
Japan Chemical Innovation Institute, AIST Tsukuba, Central 5-8, 1-1-1 Higashi, Tsukuba, Iharaki 305-8565, Japan b National Institute of Advanced Industrial Science and Technology, Tsukuba, Central 5-8, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan e Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
Abstract Additive effects of dialkylaluminum hydrides on propylene-l,3-butadiene copolymerization were investigated with an isospecific zirconocene catalyst, rac-dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride (4Ph), activated by modified methylaluminoxane. Dialkylaluminum hydrides improved the apparent selectivity for 1,2-insertion of 1,3-butadiene to give a pendant vinyl group. 13C NMR analysis of the eopolymers indicated that the dialkylaluminum hydride converted the 1,4-inserted butadiene unit in the copolymer to tetramethylene unit after methanolysis. 1. INTRODUCTION Polypropylene (PP) has been expanding its usage due to its mechanical balance and economical advantage. PP is, however, so hydrophobic that many attempts have been made to improve affinity of PP with other polar materials [1-2]. We have been developing copolymerization techniques to control the amount and location of polar groups in PP chain and succeeded in the selective introduction of carbon-carbon double bond as a precursor of polar group by the copolymerization of propylene and 1,3-butadiene using isospecific zirconocene
198
T. Ishihara et al,
catalysts [3-4]. The addition of hydrogen was found to hydrogenise the 1,4inserted butadiene units (1,4-BD) in the copolymer, and selectively produced PP with pendant vinyl groups. In this paper, therefore, we investigated the additive effects of dialkylaluminum hydrides on the copolymerization whether the dialkylaluminum hydrides react with 1,4-BD to produce PP having dialkylaluminum group on the main chain of the copolymer or not. 2. EXPERIMENTAL Materials. 4Ph commercially obtained from Boulder Scientific Company, and modified methylaluminoxane (MMAO) and other aluminum compounds purchased from Tosoh-Finechem. Co., were used without further purification. Other chemicals commercially obtained were purified according to the usual procedures. Polymerization procedure, Copolymerization of propylene with 1,3-butadiene was conducted in a 100-mL stainless steel autoclave by batch-wise operation at 0°C. Analytical procedures, 'H TSTMR and I3C TSTMR spectra were obtained in 1,1,2,2tetrachloroethane-d2 at 120 °C on a JEOL JNM-LA600 spectrometer. Molecular weights and molecular weight distributions of the copolymers were determined by a PL-GPC210 at 140 °C using o-dichlorobenzene as a solvent. 3. RESULTS AND DISCUSSION 3.1. Results of copolymerization The results of propylene-l,3-butadiene copolymerization using 4Ph-MMAO system are summarized in Table 1.
the
Table 1. Additive effects of aluminum compounds on propylene— 1,3-butadiene copolymerization*
additive
Yield (B)
Rsp (kgpolymer / mol-Zr»h) 13.1 15.8 35.8
(xlO3)
MJ Mnb
Mole fraction6 (%) 1,21,4H-1,4 BD BD -BD 1.43 0.76 0 0.23 1.26 0.63 0.26 0.4S 1.59
Selectivity {%) i *} nn
nan 0.08 2.4 35.7 65.3 0.1 34.2 84.6 DEAL-H 1.6 0.21 13.0 3.9 85.9 DiBAL-H "Polymerization conditions: solvent (toluene) = 40 mL, 4Ph = 2 jimol, MMAO = 4.0 mmol, 0 °C, 3 h, propylene concentration 1.8 mol / L, butadiene concentration 90 mmol / L. bNumber average molecular weight and molecular weight distribution determined by GPC using universal calibration.e Calculated from 'H and 13C NMR spectra. A Selectivities were the relative ratios of 1, 2—BD mole fractions to all double bonds.
32. Additive Effects ofDiatkylatuminum Hydrides
199
Dialkylaluminum hydrides, i.e., diethylaluminum hydride (DEAL-H) and diisobutylaluminum hydride (DiBAL—H), increased polymerization activities. The addition of DEAL-H did not affect the molecular weight (Mn) of the copolymer, whereas the introduction of DiBAL—H decreased the Ma value. An increase in polymerization activity accompanied by a decrease of molecular weight indicates that DiBAL-H caused chain transfer reaction. 3.2. Structures of copolymers The addition of the dialkylaluminum hydrides caused the decrease of 1,4—BD in the copolymer as observed in the *H NMR spectra (Fig. 1). The selectivity for 1, 2-BD in copolymers determined by 'H NMR are shown in Table 1.
I III-AI -II
Fig.l H NMR spectra of propylene- 1, 3- butadiene capolymer with and without DiBAL-H
[I'M
Fig, 2 " C NMR spectra of propylene-1, 3butadiene eopolymers synthesized with and without DiBAL-H.
The selectivity was improved from 65 to 85 % by the addition of the dialkylaluminum hydrides. To investigate the structures of copolymers in more details, we measured the 13C NMR spectra of copolymers obtained with and without DiBAL-H (Fig. 2). The signals assignable to pendant vinyl group and those to 1,4-BD structure were observed in both samples. The addition of DiBAL-H, however, caused the emergence of new signals derived from hydrogenated 1,4-BD (H-1,4-BD). The total mole fractions of 1,4-BD and H-1,4-BD were unchanged by the addition of the dialkylaluminum hydrides
200
T. Ishihara ct al.
(Table 1). The results indicate that the dialkylaluminum hydrides did not affect the mode of butadiene insertion but hydroaluminated the 1,4-BD units. A plausible copolymerization mechanism is shown in Scheme 1. Dialkylaluminum hydride and propylene competitively react with 7t-allyl Zr complex formed by 1,4-insertion of butadiene (A in Scheme 1). Insertion of propylene to A forms 1,4-BD in main chain (C), When dialkylalunium hydride reacts with A, hydroaluminated 1,4-BD is formed (B, D), which could incorporate successive propylene insertion more smoothly. The hydroaluminated 1,4-BD gives H—1,4—BD in main chain after methanolysis (E). Scheme 1 Reaction scheme &rpropylene-l,3-butadiene copolymerization with zirconocene— MMAO-dialkylaluminum hydride
4. CONCLUSIONS The 4Ph-MMAO-dialkylaluminum hydride system produced PP copolymer with pendant vinyl group. Although their selectivity of reduction from 1,4-BD to H—1,4—BD was lower than that with hydrogen [4], the copolymer possessed dialkylaluminum groups in main chain which can be utilized for functionalization of PP. Acknowledgements This work was supported by the New Energy and Development Organization (NEDO) through a grant for "Project on Nanostructured Polymeric Materials" under the Nanotechnology Program. References [1] T. C. Chung, Prog. Polym. Sci. 27 (2002) 39-85. [2] G. Moad, Prog. Polym. Sci. 24 (1999) 81-142. [3] T. Ishihara and T. Shiono, Macromolecules 36 (2003) 9675-9677. [4] T. Ishihara and T. Shiono, J. Am. Chem. Soc. 127 (2005) 5774-5775.