Patent ID: 8338020

Claim:
A microporous membrane comprising: (a) a first layer including ≧20.0 wt. % polymethylpentene based on the weight of the first layer; (b) a second layer which (i) includes a compatibilizer and (ii) has a composition that is not substantially the same as that of the first layer; and (c) a third layer located between the first and second layers; wherein (i) the first and third layers have substantially the same composition and substantially the same thickness and each comprises 20.0 wt. % to 45.0 wt. % of the polymethylpentene, the polymethylpentene having an Mw of 1.0×10 4 to 4.0×10 6 and a Tm≧200.0° C.; 0.0 wt. % to 45.0 wt. % of an isotactic polypropylene having an Mw≧6.0×10 5 and a Tm≧162.0° C.; and ≧10.0 wt. % polyethylene, the weight percents being based on the weight of the layer, (ii) the second layer comprises ≧5.0 wt % of the compatibilizer based on the weight of the layer, the compatibilizer comprising poly(α-olefin) excluding polyethylene homopolymer, and (iii) at least one of the first or third layers is in layer-to-layer contact with the second layer.