Supporting Data for Permeability–Strength Tradeoff in Nanoporous Polyethylene Membranes Derived from Etchable Triblock Polymer Precursors

Abstract

These files contain primary data along with associated output from instrumentation supporting all results reported in Hoehn and Hillmyer, "Permeability–Strength Tradeoff in Nanoporous Polyethylene Membranes Derived from Etchable Triblock Polymer Precursors". In this work we show the strength and toughness of nanoporous polymeric materials can limit their implementation in high performance applications. One way to increase membrane strength without using supports is to reduce membrane void fraction (f_void); however, this can negatively impact permeability. We explored this permeability–strength tradeoff using a library of polylactide-block-polyethylene-block-polylactide triblock polymers which served as precursors to nanoporous membrane materials. The triblock polymers were processed using a solvent casting technique followed by selective polylactide (PLA) removal and oxygen plasma etching to yield nanoporous polyethylene (PE) membranes. The volume fraction of the etchable block (f_PLA) allowed precise control of f_void by modifying the PLA content, determination of the compositional window for network connectivity, and elucidation of relationships between membrane porosity, permeability, and membrane strength. At f_PLA < 0.27, isolated PLA domains were unable to be completely hydrolyzed, making these compositions unsuitable for nanoporous membrane generation, and at f_PLA>0.74 we observed a transition from percolating network into isolated PE domains that were also not useful for membrane applications. Between f_void = 0.27 to 0.74, we observed a clear permeability–strength tradeoff, where lower void fraction membranes had high yield stresses (σy = 11–14 MPa) and elastic moduli (E = 400–700 MPa), but low air permeability (<6,000 L m2 hr–1 bar–1 at 0.28 bar). In contrast, high porosity membranes exhibited lower yield stresses (σy = 2–8 MPa) but higher air permeabilities (up to 8,000 L m2 hr–1 bar–1 at 0.28 bar). These findings enable future research to strategically tailor block polymer compositions to achieve desired mechanical properties and permeability in nanoporous membranes derived from block polymers.