Disordered Triblock Polymers for Nanoporous Materials with Tunable Surface Properties for Ultrafiltration Applications

Triblock polymers trapped in the fluctuating disordered state were investigated as precursors to nanoporous ultrafiltration membranes. The triblock explored is poly(lactide)-b-poly(oligoethylene glycol methyl ether methacrylate)-b-poly(styrene-s-methyl methacrylate) (PLA-POEGMA-PSMMA), where PLA is the etchable pore-forming block, POEGMA is the hydrophilic pore-lining block, and PSMMA is the matrix block. Bicontinuous microphase-separated domains were obtained thermally by heating the polymer melt above the order-disorder transition temperature (T_ODT) followed by quenching below the glass transition temperature (T_g), or isothermally by spin coating the block polymer solution at ambient conditions. POEGMA is miscible with PLA but not PSMMA and should therefore colocalize with PLA and be exposed on pore surfaces after selective PLA etching. The triblock polymers have similar ODT behavior as diblock polymers, and the presence of an accessible T_ODTin the melt depends strongly on the segregation strength χ_PLA-PSMMAN. Composite membranes with block polymer selective layers were prepared by spin coating the triblock polymer onto water-filled nylon membranes, where rapid solvent evaporation enabled the block polymer to be vitrified in the disordered state. The resulting membranes have uniform surface pores, high permeabilities, and small improvements in surface hydrophilicity, and the approach may be applied to target other surface functionalities.