Modified polypropylene-based polymer and composition comprising it

A modified polypropylene-based polymer obtained by graft modification of a propylene/α-olefin copolymer, wherein the propylene/α-olefin copolymer is polymerized in a multi stage process, the propylene/α-olefin copolymer having a xylene-soluble portion of at least 40 mass % and no greater than 85 mass %, a xylene-soluble portion (XS) intrinsic viscosity (XSIV) of at least 2.5 dl/g, and an MFR value of no greater than 3.0 g/10 min at 230° C. under a load of 2.16 kg, using, with respect to 100 parts by mass of the propylene/α-olefin copolymer, 2.0 to 3.0 parts by mass of an unsaturated carboxylic acid or its derivative and 0.4 to 0.5 parts by mass of a dialkyl peroxide;

• wherein the propylene/α-olefin copolymer has (i) an elastomer component having a mean particle size of no greater than 5 μm and (ii) a component comprising polypropylene;
• wherein the grafting ratio of the unsaturated carboxylic acid, or its derivative, to the propylene/α-olefin copolymer is 1.0 mass % to 1.4 mass %;
• and
• wherein the elastomer component forms an inter penetrating network structure with the polypropylene.