POLYOLEFIN COMPOSITIONS HAVING HIGH TENACITY

A polyolefin composition suitable for preparing single ply roofing membranes, comprising: (A) from about 15 to about 40% by weight of a crystalline copolymer of propylene with at least one alpha-olefin of formula H2C=CHR , where R is H or a C2-8 linear or branched alkyl, containing at least about 90% by weight of propylene, having solubility in xylene at room temperature lower than about 15% by weight; (B) from about 60 to about 85% by weight of an elastomeric fraction comprising: (1) a copolymer of propylene with ethylene containing about 20 to about 35% by weight ethylene, and having solubility in xylene at room temperature greater than about 70% by weight, the intrinsic viscosity of the xylene soluble fraction being higher than about 3.0 dl/g up to about 6.0 dl/g; and (2) a copolymer of ethylene with at least one alpha-olefin of formula H2C=CHR , where R is a C2-8 linear or branched alkyl, containing about 15% to 40% by weight alpha-olefin, and having solubility in xylene at room temperature greater than about 25% by weight, the intrinsic viscosity of the xylene soluble fraction ranging from about 0.5 to about 5.0 dl/g; the (1)/(2) weight ratio ranging from about 1:5 to about 5:1. The polyolefin composition of the invention, preferably prepared by sequential polymerization in at least three stages, has tensile strength at break >=25 MPa, elongation at break >=700 MPa and toughness >=150 MPa.