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 H.sub.2
C.dbd.CHR.sup.1, where R.sup.1 is H or a C.sub.2-8 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
H.sub.2 C.dbd.CHR.sup.2, where R.sup.2 is a C.sub.2-8 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 .gtoreq.25 MPa, elongation at break .gtoreq.700 MPa and toughness
.gtoreq.150 MPa.