One-Step Routes from Di- and Triblock Copolymer Precursors to Hydrophilic Nanoporous Poly(acrylic acid)-b-polystyrene

Nanoporous polystyrene with hydrophilic pores was prepared from di- and triblock copolymer precursors. The precursor material was either a poly(tert-butyl acrylate)-b-polystyrene (PtBA-b-PS) diblock copolymer synthesized by atom transfer radical polymerization (ATRP) or a polydimethylsiloxane-b-poly(tert-butyl acrylate)-b-polystyrene (PDMS-b-PtBA-b-PS) triblock copolymer synthesized by a combination of living anionic polymerization and ATRP. In the latter copolymer, PS was the matrix and mechanically stable component, PtBA was converted by acidic deprotection to hydrophilic poly(acrylic acid) (PAA) providing at the same time part of the nanoporosity, and PDMS was quantitatively etched to provide additional nanoporosity. Both the deprotection of the PtBA block and the etching of PDMS were realized by one-step operations using either anhydrous hydrogen fluoride (HF) or trifluoroacetic acid (TFA). The finding that TFA can remove PDMS is important, not least as an alternative to the more hazardous HF. The investigated di- and triblock copolymer samples were of either hexagonal or lamellar morphology. The resulting nanoporous polymers were characterized by infrared spectroscopy, small-angle X-ray scattering, and scanning electron microscopy. In contact with water, all the prepared nanoporous polymers showed spontaneous water uptake close to the amounts expected from the precursor block copolymer compositions.