Patent ID: 7658875

Claim:
A method of producing a biaxially-oriented film comprising providing an isotactic propylene polymer prepared by polymerization of propylene in the presence of an isospecific metallocene catalyst characterized by the formula: R″(C 5 (R′) 4 ) 2 MeQ p wherein each (C 5 (R′) 4 ) is a substituted cyclopentadienyl ring, each R′ is the same or different and is a hydrogen or hydrocarbyl radical having 1-20 carbon atoms, R″ is a structural bridge between the two (C 5 (R′) 4 ) rings imparting stereorigidity to the catalyst with the two (C 5 (R′) 4 ) rings being in a racemic configuration relative to Me, and R″ is selected from the group consisting of an alkylene radical having 1-4 carbon atoms, a silicon hydrocarbyl radical, a germanium hydrocarbyl radical, a phosphorus hydrocarbyl radical, a nitrogen hydrocarbyl radical, a boron hydrocarbyl radical, and an aluminum hydrocarbyl radical; Me is a group 4b, 5b or 6b metal as designated in the Periodic Table of Elements; each Q is a hydrocarbyl radical having 1-20 carbon atoms or is a halogen; and 0≦p≦3; (a) extruding the isotactic polypropylene into a sheet; and (b) stressing the extruded sheet in the transverse and longitudinal directions to form a biaxially-oriented film having a thickness of 10 microns or less and a secant modulus in the longitudinal direction of greater than about 1400 MPa and a secant modulus in the transverse direction of greater than about 2200 MPa, the polymer film having a permeability to water vapor of less than about 2.5 g/m 2 day/25 μm and a permeability to O 2 of less than about 2200 cc/m 2 day/25 μm.