Porous polyolefin membranes play an integral role in lithium-ion battery technology as the barrier preventing direct anode and cathode contact. Block polymers containing a sacrificial component have proven to be attractive precursors for nanoporous polymer membranes stemming from their unique ability to self-assemble into mesoscopically organized structures. Selective removal of the sacrificial component can leave a scaffold with well-controlled pore dimensions and porosity. This communication describes the synthesis of block polymers containing polylactide (PLA) as the sacrificial component and perfectly linear polyethylene (LPE) as the matrix phase using a combination of ring-opening polymerizations. Bicontinuous morphologies accessible over a broad composition range allow for ready tailoring of porosity. Removal of the PLA results in semicrystalline LPE with an interpenetrating void space having pore dimensions less than 100 nm. The porosity and domain size dependence on composition was corroborated by nitrogen adsorption and scanning electron microscopy. The mechanical robustness of the nanoporous samples was confirmed by tensile testing. The outstanding chemical resistance of the nanoporous LPE samples was demonstrated by treatment with concentrated strong acids over extended periods (∼1 day).