Abstract: A method for producing an ethylene polymer which comprises continuously polymerizing ethylene alone or copolymerizing ethylene and a C3-C8 ?-olefin by multistage polymerization in a plurality of polymerization reactors connected in series in the presence of a chromium catalyst having at least a part of chromium atoms converted to hexavalent chromium carried on an inorganic oxide carrier by calcination-activating in a non-reducing atmosphere, wherein an organoaluminum compound of the formula (1): (R1)xAl(OR2)y(OSiR3R4R5)z??(1) (in the above formula, R1 and R2 may be the same or different, each represents a C1-C18 alkyl group or a C6-C18 aryl group, R3, R4 and R5 may be the same or different, each represents a C1-C18 alkyl group or a C6-C18 aryl group, R1, OR2 and OSiR3R4R5 respectively may be the same or different when each has a plurality of kinds, and x, y and z are respectively 0?x?3, 0?y<3, 0?z<3, and x+y+z=3) is introduced at least one or all of the polymerization reactors.

Abstract: A method for producing an ethylene polymer which comprises continuously polymerizing ethylene alone or copolymerizing ethylene and a C3-C8 ?-olefin by multistage polymerization in a plurality of polymerization reactors connected in series in the presence of a chromium catalyst having at least a part of chromium atoms converted to hexavalent chromium carried on an inorganic oxide carrier by calcination-activating in a non-reducing atmosphere, wherein an organoaluminum compound of the formula (1): (R1)xAl(OR2)y(OSiR3R4R5)z??(1) (in the above formula, R1 and R2 may be the same or different, each represents a C1-C18 alkyl group or a C6-C18 aryl group, R3, R4 and R5 may be the same or different, each represents a C1-C18 alkyl group or a C6-C18 aryl group, R1, OR2 and OSiR3R4R5 respectively may be the same or different when each has a plurality of kinds, and x, y and z are respectively 0?x?3, 0?y<3, 0?z<3, and x+y+z=3) is introduced at least one or all of the polymerization reactors.

Abstract: The invention relates to a method for producing an ethylene polymer, comprising performing polymerization of ethylene in co-presence of hydrogen using a trialkylaluminum compound-carried chromium catalyst, wherein the chromium catalyst is obtained by calcination-activating a chromium compound that is carried on an inorganic oxide carrier in a non-reducing atmosphere to convert chromium atoms in the chromium compound into hexavalent chromium atoms for at least a portion thereof, and treating with a trialkylaluminum compound in an inert hydrocarbon solvent to carry thereon and removing to dry the solvent so that the chromium atoms are not over-reduced by the trialkylaluminum compound, and to an ethylene polymer suitable for blow molded articles obtained by the production method. The ethylene polymer of the invention have improved environment stress crack resistance (ESCR) and impact resistance in a good balance and are suitable for molded blow articles, in particular large size blow molded articles.

Abstract: A catalyst for the production of an ethylene polymer comprising a specific trivalent alkyl chromium compound, an inorganic oxide solid and optionally an organoaluminum compound (first catalyst), a catalyst for the production of an ethylene polymer comprising the specific trivalent alkyl chromium compound, a specific tetravalent alkyl chromium compound and an inorganic oxide solid (second catalyst) and a process for producing an ethylene polymer using those catalysts. The first catalyst of the present invention does not cause deterioration with the passage of time, is stable to heat and light, has greatly improved activity and can efficiently produce an ethylene copolymer with &agr;-olefin.

Abstract: The invention relates to a method for producing an ethylene polymer, comprising performing polymerization of ethylene in co-presence of hydrogen using a trialkylaluminum compound-carried chromium catalyst, wherein the chromium catalyst is obtained by calcination-activating a chromium compound that is carried on an inorganic oxide carrier in a non-reducing atmosphere to convert chromium atoms in the chromium compound into hexavalent chromium atoms for at least a portion thereof, and treating with a trialkylaluminum compound in an inert hydrocarbon solvent to carry thereon and removing to dry the solvent so that the chromium atoms are not over-reduced by the trialkylaluminum compound, and to an ethylene polymer suitable for blow molded articles obtained by the production method. The ethylene polymer of the invention have improved environment stress crack resistance (ESCR) and impact resistance in a good balance and are suitable for molded blow articles, in particular large size blow molded articles.

Abstract: A polymerization catalyst which exhibits a high activity and a good hydrogen response and thus is suitable for the production of an ethylene polymer having a wide molecular weight range can be obtained by a method using a chromium compound, an organic aluminum compound and a carrier and comprising the following steps (a) to (d): (a) contacting a chromium compound with a carrier in the presence or absence of a solvent; (b) adding an organic aluminum compound to said contacted substances at a temperature of not higher than 60° C. in an amount such that the mixing ratio of said organic aluminum compound to said chromium compound falls within the range of from 0.5/1 to 100/1 as calculated in terms of the ratio of aluminum atom/chromium atom (Al/Cr molar ratio) and that the following relationship (1) is satisfied: log10t≦0.33log10C+0.

Abstract: A blow-moldable or extrudable ethylene polymer having an excellent moldability which gives a molded product free of roughened surface, having: a number-average molecular weight Mn (V1) as determined from the amount of a terminal vinyl group by .sup.13 C-NMR measurement with respect to a fraction having a number-average molecular weight Mn of 100,000 according to GPC; and a number-average molecular weight Mn (V2) as determined from the amount of a terminal vinyl group by .sup.13 C-NMR measurement with respect to a fraction having a number-average molecular weight Mn of 10,000 according to GPC, Mn(V1) and Mn(V2) satisfying the following relationship:1.01.ltoreq.log.sub.10 {Mn(V1)/Mn(V2)}.ltoreq.3.0and having a melt flow rate (HLMFR) of from 0.1 to 70 g/10 min.

Abstract: An ethylene base polymer and a preparation method of an ethylene base polymer characterized in use of a catalyst comprising a chromium amide compound, a solid inroganic oxide calcined at 100 to 500.degree. C. and alumoxane. According to the present invention, an ethylene base polymer with a wide molecular weight distribution, excellent shock and environmental stress cracking resistances, causing no melt fracture, and suitable for film forming and blow molding can be effectively prepared.

Abstract: A process for the production of ethylenic polymers is disclosed in which an ethylenic monomer is polymerized in the presence of a catalyst comprising a chromium compound, an alumoxane and an organometallic alkoxide and/or organometallic siloxide and a carrier supporting thereon these compounds. The resultant polymer has a balanced proportion of rigidity and environmental stress cracking resistance (ESCR) and an excellent moldability property.