Olefin polymer and method for producing olefin polymer

A method for producing an olefin polymer, comprising:

• forming a propylene initial polymerization product in the presence of an olefin polymerization catalyst which is a contact reaction product of:
• an olefin polymerization solid catalyst component containing a titanium atom, a magnesium atom, a halogen atom and an internal electron donating compound, and
• a preliminary polymerization step comprising adding a first external donating compound and at least one organoaluminum to the solid catalyst component;
• wherein the at least one organoaluminum compound selected from compounds of general formula (I):
• R1pAlQ3-p (I)
• wherein R1 is an alkyl group having 1 to 6 carbon atoms, Q is a hydrogen atom or a halogen atom, p is a real number of more than 0 and not more than 3, R1s may be the same or different when two or more R1s exist, and Qs may be the same or different when two or more Qs exist, and
• wherein the first external electron donating compound is one or more organosilicon compounds having a Si—C bond and represented by the following general formula (II):
• R2Si(OR3)3 (II)
• wherein R2 is a vinyl group, an allyl group, an aralkyl group, a cycloalkyl group having 3 to 12 carbon atoms, a phenyl group, or an alkylamino group having 1 to 12 carbon atoms, R3 is an alkyl group having 1 to 4 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, a phenyl group, a vinyl group, an allyl group or an aralkyl group, and R3s may be the same or different, or one or more aminosilane compounds having a Si—N—C bond and represented by the following general formula (III):
• R42Si(NR5R6)(NR7R8) (III)
• wherein R4 is an alkyl group having 1 to 12 carbon atoms, a vinyl group, an allyl group, an aralkyl group, a cycloalkyl group having 3 to 12 carbon atoms, or a phenyl group, R4s may be the same or different, and R5, R6, R7 and R8 are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, a phenyl group, a vinyl group, an allyl group or an aralkyl group, and may be the same or different;
• and
• further forming a polypropylene part by polymerizing propylene,
• adding a second external electron donating compound to a reaction system after the preliminary polymerization step, wherein the second external electron donating compound is added in such a manner that a ratio of time for addition of the second external electron donating compound to a total polymerization time is 5 to 95%, and wherein the second external electron donating compound is higher in adsorption to a surface of the olefin polymerization solid catalyst component than the first external electron donating compound, and
• wherein the resulting olefin polymer is a propylene-based block copolymer.