| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | December 5, 2000 |
| PATENT TITLE | Propylene-ethylene copolymers processes for the production thereof and molded articles made therefrom |
| PATENT ABSTRACT |
There are provided propylene-ethylene copolymers from which there are made molded articles having excellent heat resistance and films having both low temperature heat-sealing characteristics and stiffness, processes for the production thereof and molded articles. The propylene-ethylene copolymers contain 0.01-15 mol % of an ethylene unit and are characterized by that in the chain structure determined by NMR, triad (PEP), triad (EEE) and a ratio (N.sub..alpha..beta.) of all .alpha., .beta.-methylene carbons to all propylene units are in the specified range, a weight average molecular weight is 50,000-1,500,000 and a molecular weight distribution (Mw/Mn) is 1.2-3.8. The copolymers can be produced by copolymerizing ethylene and propylene in the presence of a catalyst in which the specified chiral transition metal compound (metallocene) and aluminoxane are combined. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | September 1, 1998 |
| PATENT CT FILE DATE | January 10, 1997 |
| PATENT CT NUMBER | This data is not available for free |
| PATENT CT PUB NUMBER | This data is not available for free |
| PATENT CT PUB DATE | July 16, 1998 |
| PATENT REFERENCES CITED |
"Excellent Stereoregular Isotactic Polymerizations of Propylene with C2-Symmetric Silylene-Bridged Metallocene Catalysts" by Takaya Mise, Shinya Maya and Hiroshi Yamazaki, The Institute of Physical and Chemical Research, Wako Saitama 351-01; Chemistry Letters, The Chemical Society of Japan, 1989, pp. 1853-1856. "Propylene Homo-and Copolymerization with Ethylene Using an Ethylenebis (1-Indenyl) Zirconium Dichloride and Methylaluminoxane Catalyst System", Toshiyuki Tsutsui, Naoshi Ishimaru, Akira Mizuno, Akinori Toyoda and Norio Kashiwa; Polymer, vol. 30, Jul. 1989. "C NMR Determination of Monomer Sequence Distribution in Ethylene-Propylene Copolymers Prepared with TiCl.sup.3 -Al(C.sup.2 H.sup.5).sup.2 Cl", Masahiro Kakugo, Yukio Naito, Kooji Mizunuma, and Tatsuya Miyatake; Macromolecules, vol. 15, 1982, pp. 150-152. |
| PATENT CLAIMS |
What is claimed is: 1. A propylene-ethylene copolymer comprising 0.01-15 mol % of an ethylene unit and 99.99-85 mol % of a propylene unit, characterized in that a) the chain structure determined by NMR has the following relationships, in the unit of three monomers sequence (triad) in the copolymer chain, a-1) the relationship between the ratio of propylene-ethylene-propylene sequence (PEP) and the content of all ethylene units (C2) is represented by equation (I) 0.0070.times.C2-0.0020.ltoreq.PEP.ltoreq.0.0070.times.C2+0.0130(I) and a-2) the relationship between the ratio of three ethylenes sequence (EEE) and the content of all ethylene units (C2) is represented by equation (II) 0.ltoreq.EEE.ltoreq.0.00033.times.C2+0.0010 (II) a-3) a ratio (N.sub..alpha..beta.) of all .alpha.,.beta.-methylene carbons to all propylene units is in the range of 0-1.2 mol %, b) a weight average molecular weight (Mw) is 50,000-1,500,000, and c) a ratio (Mw/Mn) of the weight average molecular weight (Mw) to a number average molecular weight (Mn) is 1.2-3.8. 2. The propylene-ethylene copolymer of claim 1 having the relationship between the melting point (Tm) of the copolymer and the content of all ethylene units (C2) in the copolymer which is represented by equation (III ) -8.1.times.C2+156.0.ltoreq.Tm.ltoreq.-4.4.times.C2+165.0 (III). 3. A process for the production of a propylene-ethylene copolymer comprising 0.01-15 mol % of an ethylene unit and 99.99-85 mol % of a propylene unit, in which a) the chain structure determined by NMR has the following relationships, in the unit of three monomers sequence (triad) in the copolymer chain, a1) the relationship between the ratio of propylene-ethylene propylene sequence (PEP) and the content of all ethylene units (C2) is represented by equation (I) 0.0070.times.C2-0.0020.ltoreq.PEP.ltoreq.0.0070.times.C2+0.0130(I) and a-2) the relationship between the ratio of three ethylenes sequence (EEE) and the content of all ethylene units (C2) is represented by equation (II) 0.ltoreq.EEE.ltoreq.0.00033.times.C2+0.0010 (II) a-3) a ratio (N.sub..alpha..beta.) of all .alpha.,.beta.-methylene carbons to all propylene units is in the range of 0-1.2 mol %, b) a weight average molecular weight (Mw) is 50,000-1,500,000, and c) a ratio (Mw/Mn) of the weight average molecular weight (Mw) to a number average molecular weight (Mn) is 1.2-3.8, characterized in that ethylene and propylene are copolymerized in the presence of a catalyst comprising a chiral transition metal compound and an aluminoxane, the transition metal compound being represented by formula (1) ##STR4## wherein M represents a transition metal selected from the group consisting of titanium, zirconium and hafnium; X and Y may be the same or different and each represents a hydrogen, a halogen or a hydrocarbyl radical; (C.sub.5 H.sub.4-m R.sup.1.sub.m) and (C.sub.5 H.sub.4-n R.sup.2.sub.n) represent a substituted cyclopentadienyl group in which R.sup.1 and R.sup.2 may be the same or different and each represents a hydrocarbyl radical of 1 to 20 carbons which may be joined with two carbon atoms on the cyclopentadienyl ring to form one or more hydrocarbon ring which may be substituted by a hydrocarbyl radical, or a silicone-containing hydrocarbyl radical; m and n are an integer of 1-3; and Q is a divalent group capable of linking (C.sub.5 H.sub.4-m R.sup.1.sub.m) and (C.sub.5 H.sub.4-n R.sup.2.sub.n), which is selected from the group consisting of a hydrocarbyl radical, an unsubstituted silylene group and a hydrocarbyl-substituted silylene group. 4. The process for the production of a propylene-ethylene copolymer of claim 3 wherein the chiral transition metal compound is the compound of formula (1) wherein M is zirconium or hafnium, X and Y are the same or different halogen atom or hydrocarbyl group, R.sup.1 and R.sup.2 are the same or different alkyl group of 1-20 carbons and Q is a dialkylsilylene group. 5. A molded article made from a propylene-ethylene copolymer as a molding material, the copolymer comprising 0.01-15 mol % of an ethylene unit and 99.99-85 mol % of a propylene unit, in which a) the chain structure determined by NMR has the following relationships, in the unit of three monomers sequence (triad) in the copolymer chain, a-1) the relationship between the ratio of propylene-ethylene-propylene sequence (PEP) and the content of all ethylene units (C2) is represented by equation (I) 0.0070.times.C2-0.0020.ltoreq.PEP.ltoreq.0.0070.times.C2+0.0130(I) and a-2) the relationship between the ratio of three ethylenes sequence (EEE) and the content of all ethylene units (C2) is represented by equation (II) 0.ltoreq.EEE.ltoreq.0.00033.times.C2+0.0010 (II) a-3) a ratio (N.sub..alpha..beta.) of all .alpha.,.beta.-methylene carbons to all propylene units is in the range of 0-1.2 mol %, b) a weight average molecular weight (Mw) is 50,000-1,500,000, and c) a ratio (Mw/Mn) of the weight average molecular weight(Mw) to a number average molecular weight (Mn) is 1.2-3.8. 6. The molded article of claim 5 wherein the propylene-ethylene copolymer is subjected to injection molding. 7. The molded article of claim 5 wherein the propylene-ethylene copolymer is subjected to extrusion molding. 8. The molded article of claim 5 wherein the molded article is film. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
TECHNICAL FIELD This invention relates to propylene-ethylene copolymers, and more particularly it relates to propylene-ethylene copolymers having a characteristic ethylene units-chain, very small amounts of inverted propylene units and narrow molecular weight distribution and processes for the production thereof. The invention also relates to molded articles made from the propylene-ethylene copolymers. BACKGROUND ART Prior propylene-ethylene copolymers have been extensively used in the field of films or the like, by utilizing the characteristics of lower crystallizability and lower glass transition point than linear crystalline polypropylene homopolymers. However, the use has been limited in other application fields, and more improved characteristics have been required for use in those applications. For instance, low temperature heat-sealing characteristics have been required from a standpoint of energy-saving even in the film field as most extensively used. The prior art has employed a method of lowering the melting points of the copolymers with the sacrifice of the film stiffness. Thus it has been strongly demanded to reconcile stiffness and low temperature heat-sealing characteristics which conflict with each other. These prior propylene-ethylene copolymers are usually produced by copolymerizing ethylene and propylene using a titanium catalyst. However, at improvement in various properties of the propylene-ethylene copolymers produced by such copolymerization method is considered to reach substantially the limit. In recent years, there have been investigated various methods for producing olefin (co)polymers by (co)polymerizing olefins using different catalyst systems in which metallocenes are combined with aluminoxanes. For instance, Japanese Patent Kokai 3-12406, Japanese Patent Kokai 3-12407 and CHEMISTRY LETTERS, pp. 1853-1856, 1989 disclose that high stereoregular polypropylenes produced by polymerizing propylene using catalysts consisting of silylene-bridged metallocenes having the specific structures and aluminoxanes have narrow molecular weight distributions, high melting points and high rigidities. However, no concrete technique is disclosed therein on propylene-ethylene copolymers. Further, Tsutsui et al. have considered that, for the propylene-ethylene copolymers produced by copolymerizing propylene and ethylene using an ethylenebis(1-indenyl)zirconium dichloride and methylaluminoxane catalyst system, the stereoregularities thereof defined by the meso--meso triad sequence are the same as those of the copolymers produced with prior titanium-containing catalyst components, but the melting points of said propylene-ethylene copolymers produced with said metallocene and aluminoxane catalyst system are lower than those of the copolymers obtained with the titanium catalyst components, and the causes are due to larger amounts of inverted propylene units in the propylene-ethylene copolymers obtained with the metallocene-aluminoxane catalysts (T. Tsutsui et al., POLYMER, 1989, Vol. 30, 1350). Larger amounts of inverted propylene units are due to the fact that the polymerization of propylene using the titanium catalysts proceeds substantially with 1,2-insertion, whereas the polymerization of propylene using known metallocene catalysts proceeds with 2,1- and 1,3-insertions in a constant ratio. PROBLEMS TO BE SOLVED BY THE INVENTION When prior propylene-ethylene copolymers are used for molding materials, e.g., films, it is very difficult to reconcile good stiffness and good low temperature heat-sealing characteristics. The objects of the present invention are to provide propylene-ethylene copolymers having good stiffness and low temperature heat-sealing characteristics, processes for the production thereof, and molded articles made from said copolymers. The present inventors have made extensive investigation in an effort to achieve the above-mentioned objects and succeeded in producing propylene-ethylene copolymers having a characteristic ethylene units-chain, very small amounts of inverted propylene units and narrow molecular weight distribution. Further, they have found that the propylene-ethylene copolymers having specific structure produced by the present processes permit the production of films having both good stiffness and good low temperature heat-sealing characteristics and injection molded-articles having better heat resistance, and also that said copolymers have good molding properties, thus leading to the completion of the present invention. DISCLOSURE OF THE INVENTION The present first invention is directed to a propylene-ethylene copolymer comprising 0.01-15 mol % of an ethylene unit and 99.99-85 mol % of a propylene unit, characterized in that a) the chain structure determined by NMR has the following relationships, in the unit of three monomers sequence (triad) in the copolymer chain, a-1) the relationship between the ratio of propylene-ethylene-propylene sequence (PEP) and the content of all ethylene units (C2) is represented by equation (I) 0.0070.times.C2-0.0020.ltoreq.PEP.ltoreq.0.0070.times.C2+0.0130(I) and a-2) the relationship between the ratio of three ethylenes sequence (EEE) and the content of all ethylene units (C2) is represented by equation (II) 0.ltoreq.EEE.ltoreq.0.00033.times.C2+0.0010 (II) a-3) a ratio (N.sub..alpha..beta.) of all .alpha.,.beta.-methylene carbons to all propylene units is in the range of 0-1.2 mol %, b) a weight average molecular weight (Mw) is 50,000-1,500,000, and c) a ratio (Mw/Mn) of the weight average molecular weight (Mw) to a number average molecular weight (Mn) is 1.2-3.8. The second invention is directed to a process for the production of the propylene-ethylene copolymer of the first invention, characterized in that ethylene and propylene are copolymerized in the presence of a catalyst comprising a chiral transition metal compound and an aluminoxane, the transition metal compound being represented by formula (1) ##STR1## wherein M represents a transition metal selected from the group consisting of titanium, zirconium and hafnium; X and Y may be the same or different and each represents a hydrogen, a halogen or a hydrocarbyl radical; (C.sub.5 H.sub.4-m R.sup.1.sub.m) and (C.sub.5 H.sub.4-n R.sup.2.sub.n) represent a substituted cyclopentadienyl group in which R.sup.1 and R.sup.2 may be the same or different and each represents a hydrocarbyl radical of 1 to 20 carbons which may be joined with two carbon atoms on the cyclopentadienyl ring to form one or more hydrocarbon ring which may be substituted by a hydrocarbyl radical, or a silicone-containing hydrocarbyl radical; m and n are an integer of 1-3; and Q is a divalent group capable of linking (C.sub.5 H.sub.4-m R.sup.1.sub.m) and (C.sub.5 H.sub.4-n R.sup.2.sub.n), which is selected from the group consisting of a hydrocarbyl radical, an unsubstituted silylene group and a hydrocarbyl-substituted silylene group. Further, the third invention is directed to a molded article characterized by molding the propylene-ethylene copolymer of the first invention as a molding material. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows .sup.13 C NMR spectrum of the present propylene-ethylene copolymer produced in Example 1. FIG. 2 shows a flow sheet of the process for the production of the present propylene-ethylene copolymer. BEST FORM FOR THE PRACTICE OF THE INVENTION In the propylene-ethylene copolymer of the first invention, the chain structure of the copolymer, i.e., the content of all ethylene units (C2), the ratios of three monomers sequences (PEP) and (EEE) and all .alpha.,.beta.-methylene carbons are the values calculated from the results determined at 67.20 MHz and 130.degree. C. by .sup.13 C NMR spectroscopy using a mixed solution of o-dichlorobenzene/benzene bromide with 8/2 weight ratio having 20% by weight of polymer concentration. As the measuring apparatus, for example, JEOL-GX270 spectrometer (manufactured by Nihon Densi K. K. in Japan) can be used. The propylene-ethylene copolymers of the first invention are those containing the ethylene unit of 0.01-15 mol %, preferably 0.05-12 mol %, especially preferably 0.05-10 mol %. With less than 0.01 mol % of all ethylene units content, inherent characteristics of the copolymer are lost. With exceeding 15 mol %, the crystallizability of the copolymer lowers, thus leading to lowered heat resistance. By the terms of "ratio of propylene-ethylene-propylene sequence (PEP)" and "ratio of three ethylenes sequence (EEE)" in the unit of three monomers sequence (triad) in the propylene-ethylene copolymer chain as used herein, are meant respectively, the case where the sequence of propylene and ethylene forms "the ratio distributed in the sequence of propylene-ethylene-propylene (PEP)" and "the ratio distributed in the sequence of ethylene-ethylene-ethylene (EEE)" in the triad distribution in the propylene-ethylene copolymer chain determined by .sup.13 C NMR spectroscopy proposed by Kakugo et al. (Macromolecules 1982, 15, 1150-1152). In the first invention, deciding the peak assignment in the determination of .sup.13 C NMR spectra is based on the above proposal of Kakugo et al. In the propylene-ethylene copolymer of the first invention, the ratio of propylene-ethylene-propylene (PEP) is a presence ratio of the sequence unit distributed in the sequence of propylene-ethylene-propylene to all triad units, when the sequence unit (triad) distributed in the sequence of three successive monomers is considered in all propylene and ethylene units in the copolymer chain. The higher the triad (PEP), the ratio of an isolated ethylene unit interposed between the propylene units, i.e., the randomness is higher. In the propylene-ethylene copolymer of the first invention, the ratio of propylene-ethylene-propylene sequence (PEP) has the relationship represented by equation (I) 0.0070.times.C2-0.0020.ltoreq.PEP.ltoreq.0.0070.times.C2+0.0130(I) preferably by equation (I') 0.0070.times.C2.ltoreq.PEP.ltoreq.0.0070.times.C2+0.011 (I') and particularly preferably by equation (II") 0.0070.times.C2.ltoreq.PEP.ltoreq.0.0070.times.C2+0.0090 (II') in regard to the content of all ethylene units (C2, unit: mol %) in the copolymer. The propylene-ethylene copolymers wherein the ratio of propylene-ethylene-propylene sequence (PEP) is much higher than the value represented by equation (I) have not been found in the technical scope of the present invention. On the other hand, if the (PEP) ratio is too low, the low temperature heat-sealing characteristics of the films made from the copolymer deteriorate. On one hand, the ratio of three ethylenes sequence (EEE) is a presence ratio of the chain distributed in the sequence of ethylene-ethylene-ethylene to all triad units, when the sequence unit(triad) distributed in the sequence of three successive monomers is considered in all propylene and ethylene units in the copolymer chain. The higher the triad (EEE), the ratio of the ethylene unit present in the form of block in the copolymer is higher. In the propylene-ethylene copolymer of the first invention, the ratio of ethylene-ethylene-ethylene sequence (EEE) has the relationship represented by equation (II) 0.ltoreq.EEE.ltoreq.0.00033.times.C2+0.0010 (II) preferably by equation (II') 0.0033.times.C2-0.0028.ltoreq.EEE.ltoreq.0.0033.times.C2+0.0005(II') and particularly preferably by equation (II") 0.0033.times.C2-0.0022.ltoreq.EEE.ltoreq.0.0033.times.C2 (II") in regard to the content of all ethylene units (C2, unit: mol %) in the copolymer. If the ratio of ethylene-ethylene-ethylene sequence (EEE) is much higher than the range represented by equation (II), the low temperature heat-sealing characteristics of the films made from the copolymer deteriorate. On the other hand, the case where the (EEE) ratio is too low has not been found in the technical scope of the present invention. The ratio (N.sub..alpha..beta.) of all .alpha.,.beta.-methylene carbons to the content of all propylene units (C3) as defined herein is a presence ratio (N.sub..alpha..beta., unit: mol %) of all .alpha.,.beta.-methylene carbons to the content of all propylene units (C3), in the propylene-ethylene copolymer chain determined by .sup.13 C NMR spectroscopy in accordance with the method proposed by T. Tsutsui et al., in POLYMER, 1989, Vol.30, 1350. The ratio in the present invention shows 100 times the value defined by N.sub..alpha..beta. in the above Tsutsui's reference. This ratio (N.sub..alpha..beta.) is based on the spectra of .alpha.,.beta.-methylene carbons due to 1,2-insertion of propylene and insertion of ethylene subsequent to 2,1-insertion of propylene, which reflects the content of inverted units due to 2,1-insertion of propylene in the copolymer. In the propylene-ethylene copolymer of the first invention, the ratio (N.sub..alpha..beta.) of all .alpha.,.beta.-methylene carbons(unit: mol) to the content of all propylene units (C3, unit: mol) in the copolymer chain is in the range of 0-1.2 mol %, preferably 0-0.5 mol %, particularly preferably 0-0.2 mol %. If the ratio (N.sub..alpha..beta.) of all a, p-methylene carbons (unit: mol) to the content of all propylene units (C3, unit: mol) in the copolymer chain is too high, the stiffness and heat resistance of the molded article made from the copolymer lower. The propylene-ethylene copolymers of the first invention have the chain structure of the copolymer chain in which there is almost no inverted propylene unit and the ethylene unit is more randomly distributed in the copolymer. The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the propylene-ethylene copolymer in the present first invention are based on the results determined at 135.degree. C. by a gel permeation chromatography (GPC) using an o-dichlorobenzene solution with 0.05% by weight of a polymer concentration and a mixed polystyrene gel column, e.g., TSK gel GMH6-HT available from Toso K. K. in Japan. As a measuring device, GPC-150C manufactured by Waters Co. Ltd. can be used for instance. The propylene-ethylene copolymers of the first invention have the weight average molecular weight (Mw) in the range of 50,000-1,500,000, preferably 100,000-1,000,000. If the weight average molecular weight (Mw) is too high, the melt flow property of the copolymer lowers, with the result of lowered moldability. If it is too low, the strength of the molded article lowers. For the propylene-ethylene copolymer of the first invention, the ratio (Mw/Mn) of the weight average molecular weight (Mw) to a number average molecular weight (Mn) is 1.2-3.8, preferably 1.5-3.5. The ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is a measure of a molecular weight distribution. If the ratio (Mw/Mn) is too high, the molecular weight distribution becomes too broad, which leads to the deterioration of the low temperature heat-sealing characteristics of the films made from the copolymer. The propylene-ethylene copolymers having less than 1.2 of the ratio (Mw/Mn) have not yet been found in the technical scope of the present invention. The propylene-ethylene copolymers of the present first invention, due to their structural characteristics have the relationship between the melting point (Tm) of the copolymer and the content of all ethylene units (C2, unit: mol %) in the copolymer which is represented by equation (III) -8.1.times.C2+156.0.ltoreq.Tm.ltoreq.-4.4.times.C2+165.0 (III) and depending on the structural conditions, the relationship represented by equation (III') -7.2.times.C2+156.0.ltoreq.Tm.ltoreq.-4.9.times.C2+165.0 (III') and further the relationship represented by equation (III") -6.3.times.C2+156.0.ltoreq.Tm.ltoreq.-5.4.times.C2+165.0 (III") The melting point as referred to herein is a temperature showing a peak on melting which was determined by heating propylene-ethylene copolymer from room temperature to 230.degree. C. at a rate of 30.degree. C./min, keeping it at the same temperature for 10 minutes, followed by cooling down to -20.degree. C. at a rate of -20.degree. C./min, keeping it at the same temperature for 10 minutes and heating again it at a rate of 20.degree. C./min, using a DSC 7 type differential scanning calorimeter manufactured by Perkin Elmer Co. The processes of producing the propylene-ethylene copolymers of the first invention are not limited, if the propylene-ethylene copolymers thus produced satisfy each of the requirements as mentioned above. The processes using the specified metallocene catalysts of the second invention are preferred. In the present second invention, a combination of chiral transition metal compounds as the specified metallocene and aluminoxanes is used as a catalyst. Those which can be used as the metallocene can include chiral transition metal compounds represented by formula (1) ##STR2## wherein M represents a transition metal selected from the group consisting of titanium, zirconium and hafnium; X and Y may be the same or different and each represents a hydrogen, a halogen or a hydrocarbyl radical; (C.sub.5 H.sub.4-m R.sup.1.sub.m) and (C.sub.5 H.sub.4-n R.sup.2.sub.n) represent a substituted cyclopentadienyl group in which R.sup.1 and R.sup.2 may be the same or different and each represents a hydrocarbyl radical of 1 to 20 carbons which may be joined with two carbon atoms on the cyclopentadienyl ring to form one or more hydrocarbon ring which may be substituted by a hydrocarbyl radical, or a silicone-containing hydrocarbyl radical; m and n are an integer of 1-3; and Q is a divalent group capable of linking (C.sub.5 H.sub.4-m R.sup.1.sub.n) and (C.sub.5 H.sub.4-n R.sup.2.sub.n), which is selected from the group consisting of a hydrocarbyl radical, an unsubstituted silylene group and a hydrocarbyl-substituted silylene group. Preferable are the chiral transition metal compounds of formula (1) wherein M is zirconium or hafnium, R.sup.1 and R.sup.2 are the same or different alkyl group of 1 to 20 carbons, X and Y are the same or different halogen atom or hydrocarbyl group and Q is dialkylsilylene group. Concrete examples of the chiral transition metal compounds represented by formula (1) can include: rac-Dimethylsilylene bis(2-methyl-4,5,6,7-tetrahydroindenyl)zirconium dichloride, rac-Dimethylsilylene bis(2-methyl-4,5,6,7-tetrahydroindenyl)zirconium dimethyl, rac-Ethylene bis(2-methyl-4,5,6,7-tetrahydroindenyl)hafnium dichloride, rac-Dimethylsilylene bis(2-methyl-4-phenylindenyl)zirconium dichloride, rac-Dimethylsilylene bis(2-methyl-4-phenylindenyl)zirconium dimethyl, rac-Dimethylsilylene bis(2-methyl-4-phenylindenyl)hafnium dichloride, Dimethylsilylene(2,4-dimethylcyclopentadienyl)(3',5'-dimethylcyclopentadien yl)titanium dichloride, Dimethylsilylene(2,4-dimethylcyclopentadienyl)(3',5'-dimethylcyclopentadien yl)zirconium dichloride, Dimethylsilylene(2,4-dimethylcyclopentadienyl)(3',5'-dimethylcyclopentadien yl)zirconium dichloride, Dimethylsilylene(2,4-dimethylcyclopentadienyl)(3',5'-dimethylcyclopentadien yl)zirconium dimethyl, Dimethylsilylene(2,4-dimethylcyclopentadienyl)(3',5'-dimethylcyclopentadien yl)hafnium dichloride, Dimethylsilylene(2,4-dimethylcyclopentadienyl)(3',5'-dimethylcyclopentadien yl)hafnium dimethyl, Dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2',4',5'-trimethylcyclope ntadienyl)titanium dichloride, Dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2',4',5'-trimethylcyclope ntadienyl)zirconium dichloride, Dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2',4',5'-trimethylcyclope ntadienyl)zirconium dimethyl, Dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2',4',5'-trimethylcyclope ntadienyl)hafnium dichloride, and Dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2',4',5'-trimethylcyclope ntadienyl)hafnium dimethyl. Of these metallocenes, especially preferred are the following compounds: Dimethylsilylene(2,4-dimethylcyclopentadienyl)(3',5'-dimethylcyclopentadien yl)zirconium dichloride, Dimethylsilylene(2,4-dimethylcyclopentadienyl)(3',5'-dimethylcyclopentadien yl)zirconium dimethyl, Dimethylsilylene(2,4-dimethylcyclopentadienyl)(3',5'-dimethylcyclopentadien yl)hafnium dichloride, Dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2',4',5'-trimethylcyclope ntadienyl)zirconium dichloride, Dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2',4',5'-trimethylcyclope ntadienyl)zirconium dimethyl, Dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2',4',5'-trimethylcyclop entadienyl)hafnium dichloride, and Dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2',4',5'-trimethylcyclope ntadienyl)hafnium dimethyl. In the synthesis of these chiral metallocenes, a metallocene of meso form in a non-chiral structure may be formed as a by-product. In the practical use, however, all are not required to be chiral metallocenes and the meso form may be mixed. When a mixture with the meso form is used, there may be the case where the atactic polymer polymerized from the meso form is required to be removed by known process, e.g., solvent extraction or the like, so that the resulting propylene-ethylene copolymers may meet the essential requirements of the present first invention, but depending on the proportion of the meso form mixed and the propylene-ethylene copolymerization activity. Those chiral metallocenes can be formed in combination with aluminoxanes into a catalyst, but may be supported on a finely divided carrier. The finely divided carriers include inorganic or organic compounds, for which here are used finely divided solids in the form of granules or spheres having a particle diameter of 5-300 .mu.m, preferably 10-200 .mu.m. The inorganic compounds used for the carrier can include SiO.sub.2, Al.sub.2 O.sub.3, MgO, TiO.sub.2, ZnO or the mixtures thereof, e.g., SiO.sub.2 --Al.sub.2 O.sub.3, SiO.sub.2 --MgO, SiO.sub.2 --TiO.sub.2, SiO.sub.2 --Al.sub.2 O.sub.3 --MgO. Of these compounds, those comprising SiO.sub.2 or Al.sub.2 O.sub.3 as a main component are preferred. The organic compounds used for the carrier can include polymers or copolymers of .alpha.-olefin of 2-12 carbons such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and polymer or copolymer of styrene. Aluminoxanes which are combined as a catalyst component with the chiral transition metal compounds in the process of producing propylene-ethylene copolymers according to the present second invention, include organoaluminum compounds represented by the following formula (2) or (3). ##STR3## wherein R.sup.3 represents a hydrocarbyl radical of 1 to 6 carbons, preferably 1 to 4 carbons, which can concretely include an alkyl group such as methyl, ethyl, propyl, butyl, isobutyl, pentyl, hexyl; an alkenyl group such as allyl, 2-methylallyl, propenyl, isopropenyl, 2-methyl-1-propenyl, butenyl; a cycloalkyl group such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl; and an aryl group. Of these, the alkyl group is especially preferred and each R.sup.3 may be identical or different. p is an integer of 4 to 30, preferably 6 to 30, especially preferably 8 to 30. These aluminoxanes can be used singly or in combination of two or more. Also, they can be used in admixure with aluminum alkyls such as trimethyl aluminum, triethyl aluminum, tri-isopropyl aluminum, tri-isobutyl aluminum, dimethyl aluminum chloride. The aluminoxanes can be prepared under various known conditions. More specifically, the following methods can be illustrated: (1) a method of reacting a trialkyl aluminum directly with water, using an organic solvent such as toluene, ether; (2) a method of reacting an trialkyl aluminum with salts containing water of crystallization such as copper sulfate hydrate, aluminum sulfate hydrate; (3) a method of reacting an trialkyl aluminum with water impregnated in silica gel or the like; (4) a method of reacting a mixture of trimethyl aluminum and tri-isobutyl aluminum directly with water, using an organic solvent; (5) a method of reacting a mixture of trimethyl aluminum and tri-isobutyl aluminum with salts containing water of crystallization such as copper sulfate hydrate, aluminum sulfate hydrate; and (6) a method of reacting tri-isobutyl aluminum with water impregnated in silica gel, followed by reacting with trimethyl aluminum. In the process for the production of the propylene-ethylene copolymers according to the second invention, a combination of the metallocenes and the aluminoxanes is used as the catalyst. The proportion of each catalyst component used is in such a range that an aluminum atom in aluminoxane is 10-100,000 mols, preferably 50-50,000 mols, especially preferably 100-30,000 mols per mol of a transition metal atom in the metallocene. In the second invention, the propylene-ethylene copolymers of the first invention can be produced by the copolymerization of propylene and ethylene in the presence of the catalyst consisting of the above combination. As the polymerization processes can be used known (co)polymerization processes of propylene. Those processes can include a slurry copolymerization wherein propylene and ethylene are polymerized in an inert solvent including an aliphatic hydrocarbon such as butane, pentane, hexane, heptane, isooctane; an alicyclic hydrocarbon such as cyclopentane, cyclohexane, methylcyclohexane; an aromatic hydrocarbon such as toluene, xylene, ethylbenzene; and gasoline fraction and hydrogenated diesel oil; a bulk copolymerization wherein propylene itself is used as a solvent; and a gas phase copolymerization wherein propylene and ethylene are copolymerized in a gas phase. The copolymerization can be carried out by any of continuous, batchwise and semi-batchwise processes. In the copolymerization of propylene and ethylene, the above-mentioned catalysts may be fed to a copolymerization reaction system in the form of a mixture obtained by previously mixing both components of metallocene and aluminoxane in the inert solvent, or alternatively metallocene and aluminoxane may be separately fed to the reaction system. Prior to the copolymerization of propylene and etylene, the catalyst consisting of combination of metallocene and aluminoxane may be pre-activated by the polymerization reaction of said catalyst with small amounts of .alpha.-olefins, more specifically about 0.001-10 kg of .alpha.-olefins per mole of the transition metal in metallocene, and subsequently the polymerization of propylene and ethylene can be carried out. This procedure is effective in obtaining a final propylene-ethylene copolymer in good particular form. As .alpha.-olefins which can be used in the pre-activation of the catalysts, there are preferably used those of 2-12 carbons which can concretely include ethylene, propylene, butene, pentene, hexene, octene, 4-methyl-1-pentene or the like. In particular, ethylene, propylene and 4-methyl-1-pentene are preferably used. In the second invention, propylene and ethylene are copolymerized by the above-mentioned polymerization processes in the presence of the above-mentioned catalysts or the preactivated catalysts. As the copolymerization conditions can be employed similar conditions to those in the polymerization of propylene according to known conventional Ziegler catalysts. More specifically, at the polymerization temperature of -50-150.degree. C., preferably -10-100.degree. C. and the polymerization pressure of an atmospheric pressure-7 MPa, preferably 0.2-5 MPa, propylene and ethylene are fed to a polymerization reactor and then copolymerized, usually for a period of about one minute to about 20 hours. In the copolymerization, hydrogen can be added in a suitable amount for controlling the molecular weight as in the prior copolymerization processes. After completion of the copolymerization of propylene and ethylene, known after-treatments such as deactivation of the catalyst, removal of the catalyst residue, drying of the product or the like may be carried out if necessary, to produce the propylene-ethylene copolymers of the first invention. In the processes of producing the propylene-ethylene copolymers of the second invention wherein ethylene and propylene are copolymerized in the presence of the catalyst of the combined metallocene and aluminoxane, the insertion reaction of propylene is controlled to 1,2-insertion with no almost occurrence of any inverse insertion of propylene, and successive insertion of ethylene is inhibited in the insertion reaction of ethylene, so that the ethylene unit is more randomly distributed in the copolymer. According to the processes of the second invention for the production of propylene-ethylene copolymers, there are produced propylene-ethylene copolymers having a monomer chain supporting more randomly distributed ethylene unit, very small amounts of inverted propylene units and narrow molecular weight distribution. In the molded articles of the third invention, the propylene-ethylene copolymers of the first invention can be served as molding materials in the form of powders or pellets, by compounding with various additives such as antioxidants, ultraviolet absorbing agents, antistatic agents, nucleating agents, lubricants, flame retardants, antiblocking agents, colorants, inorganic or organic fillers or the like or further various synthetic resins, if necessary to form powders, or alternatively by heat melting and kneading the compounds at 190-350.degree. C. for a period of from about 20 seconds to 30 minutes and cutting into particulates to form pellets. As the molding methods can be used known processes for the molding of polypropylene such as injection molding, extrusion molding, foam molding, blow molding or the like, by which there can be produced various types of moldings such as industrial injection molded parts, various containers, unstretched or stretched films, biaxially oriented films, sheets, pipes, fibers and the like. |
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