Polyolefinic Compositions Having Good Whitening Resistance

A polymerization process for the preparation of a polypropylene composition comprising (percent by weight):

• (a) 50-77% of a crystalline propylene polymer having an amount of isotactic pentads (mmmm) measured by 13C-MNR on the fraction insoluble in xylene at 25° C., higher than 97.5 molar % and a polydispersity index ranging from 4 to
• (b) 13-28% of an elastomeric copolymer of ethylene and propylene, the copolymer having an amount of recurring units deriving from ethylene ranging from 30 to 70% and being partially soluble in xylene at ambient temperature, the polymer fraction soluble in xylene at ambient temperature having an intrinsic viscosity value ranging from 2 to 4 dl/g;
• and
• (c) 10-22% of polyethylene having an intrinsic viscosity value ranging from 1 to 3 dl/g;
• wherein in said composition, the sum of component (b) and component (c) are present in an amount of at least 25 wt %, the process comprising polymerizing with a catalyst in at least three sequential polymerisation stages wherein the crystalline polymer (a), the elastomeric polymer (b) and the polyethylene (c) are prepared in separate subsequent stages, operating in each stage, except the first stage, in the presence of the polymeric material formed and the catalyst used in the immediately preceding polymerisation stage.