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Isospecific polymerization of propylene with Metal-MCM-41
Studies in Surface Science and Catalysis 146 Park et al (Editors) © 2003 Elsevier Science B.V. Allrightsreserved
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Isospecific polymerization of propylene with Metal-MCM-41 Yasunori Oumi^, Ayako Hanai^, Toyoaki Miyazaki^, Hiroyoshi Nakajima^, Satoru Hosoda*', Toshiharu Teranishi^ and Tsuneji Sano^ ^School of Materials Science, Japan Advanced Institute of Science and Technology, Tatsunokuchi, Ishikawa 923-1292, Japan ; E-mail: t-sano(q)Jaist.ac.ip ^'Sumitomo Chemical Co., Ltd., Sodegaura, Chiba 299-0295, Japan Polymerizations of propylene were conducted using various Metal-MCM-41 prepared by the post-synthesis method. Ti-, Zr-, Hf-, Mn- and Zn-MCM-41 combined with alkylaluminiums were found to give isotactic polypropylenes with wide molecular mass distributions. 1. INTRODUCTION Since the discover of ordered mesoporous silicas such as MCM-41, MCM-48, FSM-16 and SB A-15 synthesized using surfactants, much effort has been paid to incorporation of various metals into these structures for heterogeneous catalysis and adsorption. There are a large number of papers concerning incorporation of Ti and V as well as Al atoms into the framework of mesoporous silicas by the direct hydrothermal synthesis and the post-synthesis methods. It is well known that Ti- and V-containing mesoporous silicas are active for selective oxidation of a wide variety of organic substrates with the environmentally friendly oxidant [1-3]. However, up to now no information on olefin polymerization has been reported. Of course, there are several papers concerning grafting organometallic complexes onto the surfaces of the mesopores for olefin polymerization [4-6]. In this paper, we describe for the first time the high potential of Metal-MCM-41, especially Ti-, Zr- and Hf-MCM-41 for isotactic polymerization of propylene. 2. EXPERIMENTAL Various metal-containing MCM-41 (Metal-MCM-41, Metal:Al, Ti, Mn, Zn, Ga, Zr, HO were prepared by the post-synthesis method. The parent siliceous MCM-41 was prepared following the procedure described in the literature [7]. The siliceous MCM-41 was calcined at 500°C for 10 h to decompose the surfactant (hexadecyltrimethylammoinium bromide). 1 g of calcined MCM-41 was dried at 280°C for 24 h under vacuum and then dispersed in 10 ml of dry toluene containing 3 mmol of corresponding metal compound under nitrogen. The metal compounds used for the post-synthesis were A1(CH3)3, Ti(OC4H9)4, Mn(CH3COO)2, Zn(C2H5)2, Ga(CH3)3, Zr(OC4H9)4 and Hf(OC4H9)4. The mixture was kept for 48 h at room temperature (A1-, Zn- and Ga-MCM-41) or refluxed at 110°C (Ti-, Mn-, Zr- and Hf-MCM-41). The product was filtered, washed with dry toluene several times, dried at room temperature and then calcined at 500°C in air for 5 h. Polymerizations of propylene were conducted in a 100 cm^ stainless steel autoclave equipped with a magnetic stirrer. After the reactor was filled with nitrogen, measured amounts of toluene as a solvent, alkylaluminium and Metal-MCM-41 evacuated at 400°C for 8 h were added to the reactor and aged at room temperature for 15 min. The reactor was evacuated at
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liquid nitrogen temperature, and then 7 dm^ of propylene were introduced. Polymerization was started by quickly heating the reactor up to the polymerization temperature (40°C). The polymerization reaction was terminated by adding acidified methanol. The resulting polymers were extracted with boiling o-dichlorobenzene for 8 h. The weight-average molecular weight (Mw) and molar mass distribution (Mw/Mn, Mn: number-average molecular weight) of the polymers were measured at 145°C by gel-permeation chromatography using o-dichlorobenzene as a solvent. The melting points (Tm) of the polymers were measured on a calorimeter with a heating rate of 10°C/min. ^^C NMR spectra of the polymers were measured in 1,2,4-trichloro benzene/benzene-d6 (9/1 v/v) at 140°C. 3. RESULTS AND DISCUSSION The parent siliceous MCM-41 exhibited a typical X-ray diffraction (XRD) pattern with four peaks that indicates hexagonal structure as shown in Fig.l. All of the Metal-MCM-41 samples gave slightly lower quality XRD patterns than that of the parent MCM-41. The XRD patterns were found to be free from crystalline metal oxides such as Ti02 and Zr02. This was also confirmed from FTIR and UV-Vis spectra of the Metal-MCM-41. In the FTIR spectrum of Ti-MCM-41, there is no band at 710 cm'' assigned to Ti-O-Ti, while the characteristic vibration band assigned to Ti-O-Si linkage was observed at ca. 950 cmV The UV-Vis spectrum also showed no absorption band at ca. 330 nm corresponding to octahedrally coordinated Ti species, whereas an absorption band at ca. 220 nm due to a charge transfer between framework oxygen to tetrahedral Ti(IV) was observed [8]. In the UV-Vis spectrum of Zr-MCM-41, only an adsorption band due to the oxygen to Zr(IV) charge transfer
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MCM-41 AI-MCM-41
Ti-MCM-41 Mn-MCM-41 Zn-MCM-41 Ga-MCM-41 Zr-MCM-41 Hf-MCM-41 3
5 7 2 theta (degree)
9
XRD patterns of various Metal-MCM-41 Fig. Table 1 Characteristics of various Metal-MCM-41 samples Metal-MCM-41 Bulk Si/Metal BET surface area Pore diameter Pore volume (mVg) (cm (liquid)/g) ratio {^^) 3.00 0.84 MCM-41 950 13.4 2.74 874 Al-MCM-41 0.63 30.9 2.74 Ti-MCM-41 908 0.77 862 3.00 46.1 Mn-MCM-41 0.76 714 2.74 Zn-MCM-41 8.9 0.68 12.4 2.74 735 0.62 Ga-MCM-41 2.52 718 Zr-MCM-41 6.1 0.61 2.74 0.61 743 13.5 Hf-MCM-41
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transition was observed at ca. 210 nm [9]. The N2 adsorption isotherms on the Metal-MCM-41 were found to exhibit sharp inflective characteristics of capillary condensation at the relative pressure of ca. 0.3, although a slight reduction in the amounts of N2 adsorbed was observed. The BET surface areas, pore diameters and pore volumes calculated from the isotherms are summarized in Table 1. Next, polymerizations of propylene were conducted using the various Metal-MCM-41. Table 2 also summarizes the results of propylene polymerization. When the Metal-MCM-41 was combined with A1(/-C4H9)3, the Ti-, Mn-, Zn-, Zr- and Hf-MCM-41 displayed activity and gave selectively isotactic polypropylene (Run Nos. 3, 4, 5, 7, 8). No polymer was obtained when the Al- and Ga-MCM-41 as well as the parent siliceous MCM-41 were used. Table 2 Propylene polymerization with Metal-MCM-41/ A1(/-C4H9)3 catalyst^^ Tm Run Metal-MCM-4 lO'^Mw Mw/Mn [mmmm] Activity 1 No. (g-PP/Metal-mol • h) CC) (%) MCM-41 0 1 2 Al-MCM-41 trace 153.7 42 Ti-MCM-41 44 38 1,296 3 4 154.9 7.0 Mn-MCM-41 40.3 17 27 39 159.0 Zn-MCM-41 1.35 5 28 63 Ga-MCM-41 6 trace 160.3 18 34 Zr-MCM-41 45 190 7 157.4 19 12 Hf-MCM-41 40 293 8 a) Metal-MCM-41=0.5 g, Al (from Al(/-C4H9)3)/Metal=2, Toluene=30 cm\ Propylcne=7 dm-\STP), Temp.=40°C, Time=2h As the Ti-MCM-41 showed the highest activity among the Metal-MCM-41 prepared, an influence of organometallic cocatalyst on the polymerization performance of the Ti-MCM-41 was studied. As listed in Table 3, it was found that the polymerization activity is strongly dependent on the kind and amount of alkylaluminium used. Namely, the order of the cocatalytic activity was follows: A1(C2H5)2C1 > A1(/-C4H9)3 > MAO(methylalumoxane) > A1(C2H5)3 > A1(CH3)3. The polymerization activity decreased gradually with an increase in the amount of A1(/-C4H9)3. As the use of Zn(C2H5)2 an Ga(CH3)3 in place of organoaluminiums did not give polymer (Run Nos. 17, 18), the addition of organoaluminiums seems to be essential for formation of active species in the isotactic polymerization of propylene. Although the formation mechanism of active species is not clear at the present stage, we have now speculated that the active species are generated by dissociation of Si-O-Ti bond through reaction with alkylaluminium, resulting in formation of Ti-alkyl bonds. We further tried to check the possibility of elution of active Ti species from the MCM-41 framework into the liquid phase during aging before polymerization. The mixture of Ti-MCM-41 and A1(/-C4H9)3 was brought into contact in toluene, and propylene polymerization was conducted using the solution fraction. However, no polymer was obtained, indicating that the polymerization took place within the Ti-MCM-41 structure. To characterize polypropylenes obtained, the polymers were extracted using boiling o-dichlorobenzene, which is commonly used for extraction of polypropylene produced with the conventional heterogeneous Ziegler-Natta catalyst. However, the polymer could not be extracted completely from the Metal-MCM-41. About 40-60% of polymer was remained in
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the mesopores of Metal-MCM-41. As it is well recognized that cross-linking of polypropylene hardly takes place during polymerization and extraction processes, this suggests strong interaction between the occluded polymer and pore walls. However, we could not explain the exact reason at the present stage and a further study is now in progress. Therefore, the boiling o-dichlorobenzene soluble parts were analyzed and some analytical data are listed in Tables 2 and 3. The melting point (Tm) and the molar mass distribution (Mw/Mn) of polypropylene produced with A1(/-C4H9)3 were >155°C and >25, respectively. The isotacticity [mmmm] pentad was 40-60, which was considerably smaller than that expected from the Tm value. Polymerization of ethylene was also conducted using the same catalyst system (Run No. 14). The polymerization activity was approximately 10 times larger than that of propylene. The Mw/Mn was found to be more than 100, indicating an existence of multi active species within the Ti-MCM-41. From all above results, it was concluded that the Ti-, Zr- and Hf-MCM-41 have the high potential for isotactic polymerization of propylene in spite of the absence of specific organic ligands. Table 3 Propylene polymerization with Ti-MCM-41 using various organometallic cocatalysts"^^ Run Cocatalyst Metal/Ti Activity Tm 10' Mw Mw/Mn [mmmm] No. (g-pp/Ti-mol • h) (°C) (%) 158.2 9 55 60 50 148 A1(CH3)3 222 10 A1(C2H5)3 50 0 11 A1(/-C4H9)3 0 " 42 44 153.7 1,296 2 3 38 '' 704 12 24 158.7 10 61 55 " 574 39 13 154.9 50 57 51 14b) " 46 124 2 134.2 5,370 944 12 15 A1(C2H5)2C1 50 26 158.0 30 426 16 M A O 50 161.4 30 16 43 trace 17 Zn(C2H5)2 50 18 Ga(CH3)3 trace 50 a) Ti-MCM-41 =0.5 g, Toluenc=30 cm\ Propylcnc-7 dm^(STP), Tcmp.=40°C, Timc=2 h b) Ethylene was used as monomer instead of propylene. Polymerization timc=l h REFERENCES 1. R T. Tanev, M. Chibwe and T. J. Pinnavaia, Nature, 368 (1994) 321. 2. A. Corma, M. T. Navarro and J. Perez-Paricnte, Chem. Commun.. (1994) 147. 3. T. Tatsumi, K. A. Koyano and N. Igarashi, Chem. Commun., (1998) 325. 4. Y. S. Ko, T. K. Han, J. W. Park and S. I. Woo, Macromol. Rapid Commun., 17 (1996) 749. 5. J. Tudor and D. O'Hare, Chem. Commun., (1997) 603. 6. K. Kageyama, J. Tamazawa and T. Aida, Science, 285 (1999) 2113. 7. J. M. Kim, J. H. Kwak, S. Jun and R. Ryoo, J. Phys. Chem., 99 (1995) 16742. 8. L. Marchese, T. Maschmeyer, E. Gianotti, S. Coluccia and J. M. Thomas, J. Phys. Chem. B, 101 (1997)8836. 9. K. A. Vercruysse, D. M. Klingeleers, T. Colling and P. A. Jacobs, Stud. Surf Sci. Catal., 117(1998)469.
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Isospecific polymerization of propylene with Metal-MCM-41 Yasunori Oumi^, Ayako Hanai^, Toyoaki Miyazaki^, Hiroyoshi Nakajima^, Satoru Hosoda*', Toshiharu Teranishi^ and Tsuneji Sano^ ^School of Materials Science, Japan Advanced Institute of Science and Technology, Tatsunokuchi, Ishikawa 923-1292, Japan ; E-mail: t-sano(q)Jaist.ac.ip ^'Sumitomo Chemical Co., Ltd., Sodegaura, Chiba 299-0295, Japan Polymerizations of propylene were conducted using various Metal-MCM-41 prepared by the post-synthesis method. Ti-, Zr-, Hf-, Mn- and Zn-MCM-41 combined with alkylaluminiums were found to give isotactic polypropylenes with wide molecular mass distributions. 1. INTRODUCTION Since the discover of ordered mesoporous silicas such as MCM-41, MCM-48, FSM-16 and SB A-15 synthesized using surfactants, much effort has been paid to incorporation of various metals into these structures for heterogeneous catalysis and adsorption. There are a large number of papers concerning incorporation of Ti and V as well as Al atoms into the framework of mesoporous silicas by the direct hydrothermal synthesis and the post-synthesis methods. It is well known that Ti- and V-containing mesoporous silicas are active for selective oxidation of a wide variety of organic substrates with the environmentally friendly oxidant [1-3]. However, up to now no information on olefin polymerization has been reported. Of course, there are several papers concerning grafting organometallic complexes onto the surfaces of the mesopores for olefin polymerization [4-6]. In this paper, we describe for the first time the high potential of Metal-MCM-41, especially Ti-, Zr- and Hf-MCM-41 for isotactic polymerization of propylene. 2. EXPERIMENTAL Various metal-containing MCM-41 (Metal-MCM-41, Metal:Al, Ti, Mn, Zn, Ga, Zr, HO were prepared by the post-synthesis method. The parent siliceous MCM-41 was prepared following the procedure described in the literature [7]. The siliceous MCM-41 was calcined at 500°C for 10 h to decompose the surfactant (hexadecyltrimethylammoinium bromide). 1 g of calcined MCM-41 was dried at 280°C for 24 h under vacuum and then dispersed in 10 ml of dry toluene containing 3 mmol of corresponding metal compound under nitrogen. The metal compounds used for the post-synthesis were A1(CH3)3, Ti(OC4H9)4, Mn(CH3COO)2, Zn(C2H5)2, Ga(CH3)3, Zr(OC4H9)4 and Hf(OC4H9)4. The mixture was kept for 48 h at room temperature (A1-, Zn- and Ga-MCM-41) or refluxed at 110°C (Ti-, Mn-, Zr- and Hf-MCM-41). The product was filtered, washed with dry toluene several times, dried at room temperature and then calcined at 500°C in air for 5 h. Polymerizations of propylene were conducted in a 100 cm^ stainless steel autoclave equipped with a magnetic stirrer. After the reactor was filled with nitrogen, measured amounts of toluene as a solvent, alkylaluminium and Metal-MCM-41 evacuated at 400°C for 8 h were added to the reactor and aged at room temperature for 15 min. The reactor was evacuated at
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liquid nitrogen temperature, and then 7 dm^ of propylene were introduced. Polymerization was started by quickly heating the reactor up to the polymerization temperature (40°C). The polymerization reaction was terminated by adding acidified methanol. The resulting polymers were extracted with boiling o-dichlorobenzene for 8 h. The weight-average molecular weight (Mw) and molar mass distribution (Mw/Mn, Mn: number-average molecular weight) of the polymers were measured at 145°C by gel-permeation chromatography using o-dichlorobenzene as a solvent. The melting points (Tm) of the polymers were measured on a calorimeter with a heating rate of 10°C/min. ^^C NMR spectra of the polymers were measured in 1,2,4-trichloro benzene/benzene-d6 (9/1 v/v) at 140°C. 3. RESULTS AND DISCUSSION The parent siliceous MCM-41 exhibited a typical X-ray diffraction (XRD) pattern with four peaks that indicates hexagonal structure as shown in Fig.l. All of the Metal-MCM-41 samples gave slightly lower quality XRD patterns than that of the parent MCM-41. The XRD patterns were found to be free from crystalline metal oxides such as Ti02 and Zr02. This was also confirmed from FTIR and UV-Vis spectra of the Metal-MCM-41. In the FTIR spectrum of Ti-MCM-41, there is no band at 710 cm'' assigned to Ti-O-Ti, while the characteristic vibration band assigned to Ti-O-Si linkage was observed at ca. 950 cmV The UV-Vis spectrum also showed no absorption band at ca. 330 nm corresponding to octahedrally coordinated Ti species, whereas an absorption band at ca. 220 nm due to a charge transfer between framework oxygen to tetrahedral Ti(IV) was observed [8]. In the UV-Vis spectrum of Zr-MCM-41, only an adsorption band due to the oxygen to Zr(IV) charge transfer
100 200 210
MCM-41 AI-MCM-41
Ti-MCM-41 Mn-MCM-41 Zn-MCM-41 Ga-MCM-41 Zr-MCM-41 Hf-MCM-41 3
5 7 2 theta (degree)
9
XRD patterns of various Metal-MCM-41 Fig. Table 1 Characteristics of various Metal-MCM-41 samples Metal-MCM-41 Bulk Si/Metal BET surface area Pore diameter Pore volume (mVg) (cm (liquid)/g) ratio {^^) 3.00 0.84 MCM-41 950 13.4 2.74 874 Al-MCM-41 0.63 30.9 2.74 Ti-MCM-41 908 0.77 862 3.00 46.1 Mn-MCM-41 0.76 714 2.74 Zn-MCM-41 8.9 0.68 12.4 2.74 735 0.62 Ga-MCM-41 2.52 718 Zr-MCM-41 6.1 0.61 2.74 0.61 743 13.5 Hf-MCM-41
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transition was observed at ca. 210 nm [9]. The N2 adsorption isotherms on the Metal-MCM-41 were found to exhibit sharp inflective characteristics of capillary condensation at the relative pressure of ca. 0.3, although a slight reduction in the amounts of N2 adsorbed was observed. The BET surface areas, pore diameters and pore volumes calculated from the isotherms are summarized in Table 1. Next, polymerizations of propylene were conducted using the various Metal-MCM-41. Table 2 also summarizes the results of propylene polymerization. When the Metal-MCM-41 was combined with A1(/-C4H9)3, the Ti-, Mn-, Zn-, Zr- and Hf-MCM-41 displayed activity and gave selectively isotactic polypropylene (Run Nos. 3, 4, 5, 7, 8). No polymer was obtained when the Al- and Ga-MCM-41 as well as the parent siliceous MCM-41 were used. Table 2 Propylene polymerization with Metal-MCM-41/ A1(/-C4H9)3 catalyst^^ Tm Run Metal-MCM-4 lO'^Mw Mw/Mn [mmmm] Activity 1 No. (g-PP/Metal-mol • h) CC) (%) MCM-41 0 1 2 Al-MCM-41 trace 153.7 42 Ti-MCM-41 44 38 1,296 3 4 154.9 7.0 Mn-MCM-41 40.3 17 27 39 159.0 Zn-MCM-41 1.35 5 28 63 Ga-MCM-41 6 trace 160.3 18 34 Zr-MCM-41 45 190 7 157.4 19 12 Hf-MCM-41 40 293 8 a) Metal-MCM-41=0.5 g, Al (from Al(/-C4H9)3)/Metal=2, Toluene=30 cm\ Propylcne=7 dm-\STP), Temp.=40°C, Time=2h As the Ti-MCM-41 showed the highest activity among the Metal-MCM-41 prepared, an influence of organometallic cocatalyst on the polymerization performance of the Ti-MCM-41 was studied. As listed in Table 3, it was found that the polymerization activity is strongly dependent on the kind and amount of alkylaluminium used. Namely, the order of the cocatalytic activity was follows: A1(C2H5)2C1 > A1(/-C4H9)3 > MAO(methylalumoxane) > A1(C2H5)3 > A1(CH3)3. The polymerization activity decreased gradually with an increase in the amount of A1(/-C4H9)3. As the use of Zn(C2H5)2 an Ga(CH3)3 in place of organoaluminiums did not give polymer (Run Nos. 17, 18), the addition of organoaluminiums seems to be essential for formation of active species in the isotactic polymerization of propylene. Although the formation mechanism of active species is not clear at the present stage, we have now speculated that the active species are generated by dissociation of Si-O-Ti bond through reaction with alkylaluminium, resulting in formation of Ti-alkyl bonds. We further tried to check the possibility of elution of active Ti species from the MCM-41 framework into the liquid phase during aging before polymerization. The mixture of Ti-MCM-41 and A1(/-C4H9)3 was brought into contact in toluene, and propylene polymerization was conducted using the solution fraction. However, no polymer was obtained, indicating that the polymerization took place within the Ti-MCM-41 structure. To characterize polypropylenes obtained, the polymers were extracted using boiling o-dichlorobenzene, which is commonly used for extraction of polypropylene produced with the conventional heterogeneous Ziegler-Natta catalyst. However, the polymer could not be extracted completely from the Metal-MCM-41. About 40-60% of polymer was remained in
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the mesopores of Metal-MCM-41. As it is well recognized that cross-linking of polypropylene hardly takes place during polymerization and extraction processes, this suggests strong interaction between the occluded polymer and pore walls. However, we could not explain the exact reason at the present stage and a further study is now in progress. Therefore, the boiling o-dichlorobenzene soluble parts were analyzed and some analytical data are listed in Tables 2 and 3. The melting point (Tm) and the molar mass distribution (Mw/Mn) of polypropylene produced with A1(/-C4H9)3 were >155°C and >25, respectively. The isotacticity [mmmm] pentad was 40-60, which was considerably smaller than that expected from the Tm value. Polymerization of ethylene was also conducted using the same catalyst system (Run No. 14). The polymerization activity was approximately 10 times larger than that of propylene. The Mw/Mn was found to be more than 100, indicating an existence of multi active species within the Ti-MCM-41. From all above results, it was concluded that the Ti-, Zr- and Hf-MCM-41 have the high potential for isotactic polymerization of propylene in spite of the absence of specific organic ligands. Table 3 Propylene polymerization with Ti-MCM-41 using various organometallic cocatalysts"^^ Run Cocatalyst Metal/Ti Activity Tm 10' Mw Mw/Mn [mmmm] No. (g-pp/Ti-mol • h) (°C) (%) 158.2 9 55 60 50 148 A1(CH3)3 222 10 A1(C2H5)3 50 0 11 A1(/-C4H9)3 0 " 42 44 153.7 1,296 2 3 38 '' 704 12 24 158.7 10 61 55 " 574 39 13 154.9 50 57 51 14b) " 46 124 2 134.2 5,370 944 12 15 A1(C2H5)2C1 50 26 158.0 30 426 16 M A O 50 161.4 30 16 43 trace 17 Zn(C2H5)2 50 18 Ga(CH3)3 trace 50 a) Ti-MCM-41 =0.5 g, Toluenc=30 cm\ Propylcnc-7 dm^(STP), Tcmp.=40°C, Timc=2 h b) Ethylene was used as monomer instead of propylene. Polymerization timc=l h REFERENCES 1. R T. Tanev, M. Chibwe and T. J. Pinnavaia, Nature, 368 (1994) 321. 2. A. Corma, M. T. Navarro and J. Perez-Paricnte, Chem. Commun.. (1994) 147. 3. T. Tatsumi, K. A. Koyano and N. Igarashi, Chem. Commun., (1998) 325. 4. Y. S. Ko, T. K. Han, J. W. Park and S. I. Woo, Macromol. Rapid Commun., 17 (1996) 749. 5. J. Tudor and D. O'Hare, Chem. Commun., (1997) 603. 6. K. Kageyama, J. Tamazawa and T. Aida, Science, 285 (1999) 2113. 7. J. M. Kim, J. H. Kwak, S. Jun and R. Ryoo, J. Phys. Chem., 99 (1995) 16742. 8. L. Marchese, T. Maschmeyer, E. Gianotti, S. Coluccia and J. M. Thomas, J. Phys. Chem. B, 101 (1997)8836. 9. K. A. Vercruysse, D. M. Klingeleers, T. Colling and P. A. Jacobs, Stud. Surf Sci. Catal., 117(1998)469.