Propylene block copolymer, process for producing the same, and resin composition comprising the same

A process for producing a propylene block copolymer comprising:

• (a) a propylene homopolymer part having
• (i) an insoluble amount on xylene extraction at 25.degree. C. of 99.0% by weight or more;
• (ii) an isotactic pentad fraction of 98.0% or more;
• (iii) an isotactic average chain length of 500 or more;
• and
• (iv) a total amount of fractions having an isotactic average chain length of 800 or more obtained in a column chromatographic separation of 10% by weight or more,
• and
• (b) a copolymer part comprising propylene and at least one of ethylene and an .alpha.-olefin having from 4 to 12 carbon atoms,
• the proportion of said propylene homopolymer part (a) being from 50 to 97% by weight based on the total amount of said propylene homopolymer part (a) and said copolymer part (b), and the proportion of said copolymer part (b) being from 3 to 50% by weight based on the total amount of said propylene homopolymer part (a) and said copolymer part (b),
• said process comprising the steps of:
• treating a solid catalyst comprising a magnesium compound, a titanium compound, a halogen-containing compound, and an electron-donating compound, with a titanium compound represented by formula TiX.sub.a.Y.sub.b, wherein X represents Cl, Br, or I;
• Y represents an electron-donating compound;
• a represents an integer of 3 or 4;
• and b represents an integer of 3 or less;
• washing said solid catalyst with a halogen-containing compound and then with a hydrocarbon to produce a modified polymerization catalyst;
• and
• polymerizing propylene and at least one of ethylene and an .alpha.-olefin having from 4 to 12 carbon atoms in the presence of said modified polymerization catalyst.

A propylene block copolymer resin composition comprising

• a propylene block copolymer comprising:
• (a) a propylene homopolymer part having
• (i) an insoluble amount on xylene extraction at 25.degree. C. of 99.0% by weight or more;
• (ii) an isotactic pentad fraction of 98.0% or more;
• (iii) an isotactic average chain length of 500 or more;
• and
• (iv) a total amount of fractions having an isotactic average chain length of 800 or more obtained in a column chromatographic separation of 10% by weight or more, and
• (b) a copolymer part comprising propylene and at least one of ethylene and an .alpha.-olefin having from 4 to 12 carbon atoms,
• the proportion of said propylene homopolymer part (a) being from 50 to 97% by weight based on the total amount of said propylene homopolymer part (a) and said copolymer part (b), and the proportion of said copolymer part (b) being from 3 to 50% by weight based on the total amount of said propylene homopolymer part (a) and said copolymer part (b), and
• a nucleating agent in an amount of from 0.05 to 30% by weight based on the amount of said propylene block copolymer.