Patent ID: 8841032

Claim:
A membrane comprising a polymer mixture comprising: (a) polymethylpentene having a Tm≧200.0°C., and an MFR≦80.0 dg/min; (b) a first polyethylene having an Mw<1.0 ×10 6 , an MWD≦15.0, an amount of terminal unsaturation ≦0.20 per 1.0 ×10 4 carbon atoms and a Tm≧131.0°C.; and (c) a second polyethylene having a Tm<131.0° C., wherein the membrane contains ≦1.0 wt. % of polyethylene having a terminal unsaturation amount >0.20 per 1.0 ×10 4 carbon atoms and (i) is microporous; (ii) has a meltdown temperature ≧180.0°C.; (iii) has a shutdown temperature ≦131.0°C.; and (iv) has a 170° C. TD heat shrinkage ≦30.0%.