Porous membranes with multiple zones having different pore sizes

A porous membrane comprising:

• a first zone, the first zone comprising a crystallizable polymer;
• and a first melting nucleating agent, the first melting nucleating agent having a first concentration in the first zone, the first zone having a first average pore size;
• and
• a second zone, the second zone comprising a crystallizable polymer;
• and a second melting nucleating agent, the second melting nucleating agent having a second concentration in the second zone, the second zone having a second average pore size,
• wherein the crystallizable polymer is the same in the first zone and second zone,
• wherein the first average pore size is not the same as the second average pore size,
• wherein the first nucleating agent and the second nucleating agent are the same or different,
• wherein the first concentration and the second concentration agent are the same or different and
• with the proviso that the first nucleating agent and the first concentration are not the same as the second nucleating agent and the second concentration.

A method of making a porous membrane the method comprising:

• forming a first composition in a first extruder, the first composition comprising a first crystallizable polymer, a first nucleating agent and a diluent, wherein the first composition has a first concentration of the first nucleating agent, and wherein the first extruder is operated at a first specific energy input;
• forming a second composition in a second extruder, the second composition comprising a second crystallizable polymer and a diluent, wherein the second extruder is operated at a second specific energy input;
• coextruding the first composition and the second composition to form a multilayer article;
• and
• cooling the multilayer article to allow phase separation of the diluent from the crystallizable polymers to form a porous membrane
• wherein the first specific energy input is not the same as the second specific energy input,
• wherein the second composition further comprises a second nucleating agent, the second nucleating agent being present at a second concentration in the second composition, and
• wherein the first concentration of the first nucleating agent is different than the second concentration of the second nucleating agent, and further
• wherein the first composition and second composition are extruded through a multi-manifold die.

A method of making a porous membrane the method comprising:

• forming a first composition in a first extruder, the first composition comprising a first crystallizable polyolefin polymer, a first nucleating agent and a diluent, wherein the first composition has a first concentration of the first nucleating agent;
• forming a second composition in a second extruder, the second composition comprising a second crystallizable polyolefin polymer, a second nucleating agent and a diluent, wherein the second composition has a second concentration of the second nucleating agent;
• coextruding the first composition and the second composition to form a multilayer article;
• and
• cooling the multilayer article to allow phase separation of the diluent from the crystallizable polymers to form a porous membrane,
• wherein the crystallizable polymer is the same in the first zone and second zone,
• wherein the first nucleating agent and the second nucleating agent are the same or different,
• wherein the first concentration and the second concentration agent are the same or different and
• with the proviso that the first nucleating agent and the first concentration are not the same as the second nucleating agent and the second concentration.