Biaxially-oriented metallocene-based polypropylene films having reduced thickness

A polymer film product comprising a biaxially oriented polypropylene film having a thickness of about 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 of less than about 2.5 g/m2day/25 μm and a permeability to O2 of less than about 2200 cc/m2day/25 μm, and wherein the polypropylene film is formed from isotactic polypropylene having a xylene solubles in the amount of less than about 1% by weight of polypropylene and having 2,1-insertions of between about 0.1 to 1%, the isotactic polypropylene prepared by the polymerization of propylene in the presence of an isospecific metallocene catalyst characterized by the formula:

• R″(C5(R′)4)2MeQp
• wherein each (C5(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 (C5(R′)4) rings imparting stereorigidity to the catalyst with the two (C5(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 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″(C5(R′)4)2MeQp
• wherein each (C5(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 (C5(R′)4) rings imparting stereorigidity to the catalyst with the two (C5(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 about 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/m2day/25 μm and a permeability to O2 of less than about 2200 cc/m2day/25 μm.