Patent ID: 7026403

Claim:
A process for preparing a thermoplastic membrane, the process comprising: (a) polymerizing propylene or a mixture of propylene and one or more monomers selected from C 2 or C 3 –C 20 alpha olefins in the presence of a polymerization catalyst wherein a substantially isotactic propylene polymer containing at least 90% by weight polymerized propylene is obtained to form a propylene polymer, wherein said propylene polymer is a stereoregular polypropylene containing less than 7% by weight of units derived from ethylene or alpha-olefin monomer containing from 4 to 8 carbon atoms and having a melting point, as determined by DSC, greater than 130° C., and a heat of fusion greater than 80 J/g; (b) polymerizing a mixture of ethylene and propylene in the presence of a chiral metallocene catalyst, wherein a crystallizable copolymer of ethylene and propylene is obtained comprising up to 35% by weight ethylene, containing isotactically crystallizable propylene sequences and having a melting point, as determined by DSC, in the range of from 25° C. to 70° C., and a heat of fusion of from 2 J/g to 25 J/g; and (c) blending the propylene polymer of step (a) with the crystallizable copolymer of step (b) to form a blend.