Polypropylene block-copolymer resin and process for producing it

A process for producing a polypropylene block copolymer resin in a continuous multistage polymerization process, comprising

• (A) in a first stage, polymerizing propylene in the substantial absence of hydrogen, in the presence of a polymerization catalyst formed from
• (a) a solid titanium catalyst component comprising titanium, magnesium, halogen and electron donor,
• (b) an organometallic catalyst component and,
• (c) an organosilic compound catalyst component having at least one cyclic group selected from the group consisting of cyclopentyl group, cyclopentenyl group and cyclopentadienyl group or derivative of any of said cyclic groups;
• to form a higher molecular weight polypropylene part (A), having an intrinsic viscosity (η) of from 6 to 13 dl/g, wherein the amount of said polypropylene part (A) is from 10 to 50 percent by weight, based on the total weight of said polypropylene block copolymer resin;
• (B) in a second stage, polymerizing propylene in the presence of said polymerization catalyst to form a lower molecular weight polypropylene part (B), having an intrinsic viscosity (η) lower than 6 dl/g, wherein the amount of said polypropylene part (B) is from 10 to 80 percent by weight, based on the total weight of said polypropylene block copolymer resin;
• and,
• (C) in a third stage, copolymerizing ethylene and α-olefin to form an ethylene/α-olefin copolymer part (C), having an intrinsic viscosity (n) of from 0.1 to 13 dl/g, wherein the amount of said copolymer part (C) is from 1 to 40 percent by weight, based on the total weight of said polypropylene block copolymer resin;
• said first stage, second stage and third stage polymerizations being effected continuously in any order, and
• wherein, when said polypropylene block copolymer resin is subjected to a dissolution fractionation with paraxylene, the constituent components comprise
• (X) 2 to 39% by weight of a component soluble in paraxylene at 23° C. and
• (Y) 61 to 98% by weight of a component soluble in paraxylene at 135° C., but insoluble in paraxylene at 23° C.;
• and further wherein, said polypropylene block copolymer resin has the following properties:
• (1) a melt flow rate (MFR), determined at 230° C., under a load of 2.16 kg, of0.01 to 5 g/10 min. and
• (2) a molecular weight distribution, Mw/Mn, determined by gel permeation chromatography (GPC), of 6 to 20 and Mz/Mw of at least 3.5.