Polymeric material and its manufacture and use

A method for producing a microporous membrane comprising the steps of:

• combining a diluent or solvent and a first polyolefin composition to prepare a first polyolefin solution, the first polyolefin composition comprising greater than about 90 mole % propylene monomer and having one or more of the following:
• i. an intrinsic viscosity greater than about 10 dl/g;
• ii. a heat of fusion greater than about 108 J/g, a melting point of 165° C. or greater;
• iii. a molecular weight greater than about 1.5×106;
• iv. a molecular weight distribution of from about 2.5 to about 7;
• v. a Melt Flow Rate at 230° C. of less than about 0.01 dg/minute;
• vi. an amount of extractable species of 0.5 wt. % or less based on the weight of the polyolefin composition;
• vii. a meso pentad fraction of greater than about 96 mol % mmmm pentads;
• and
• viii. an amount of stereo defects less than about 50 per 10,000 carbon atoms;
• extruding the first polyolefin solution through at least one die to form an extrudate;
• removing at least a portion of the membrane-forming solvent from the cooled extrudate or extrudate to form a solvent-removed sheet;
• and
• drying the sheet to form the microporous membrane.