Nanochannel Array Plastics with Tailored Surface Chemistry

Abstract

The utilization of nanoporous substrates in applications such as selective ion transport, biomolecule separation, seeded templating, and catalysis necessitates the ability to efficiently control pore surface properties. We approached this task by preparing nanoporous polymer monoliths from ABC triblock copolymer precursors that assemble into a cylindrical morphology, where the A block constitutes matrix, C is the removable minor component, and B provides the functionality on the surface of the pores. Polystyrene-polydimethylacrylamide-polylactide (PS-PDMA-PLA) triblock copolymers were prepared by a combination of controlled ring-opening and free-radical polymerization techniques. After selective etching of the PLA cylinders from shear-aligned monoliths, a nanoporous polystyrene matrix containing a hexagonally packed array of hydrophilic, PDMA-coated channels was obtained. Extremely high degrees of alignment and order could be attained, and nanoporous substrates with second-order orientation factors of as high as 0.96 were prepared. PDMA brushes inside the pores were then hydrolyzed in a controlled fashion to introduce a desired number of carboxylic acid groups to the internal pore surface. Carbodiimide mediated couplings with amines were then used to confirm the accessibility of the interior acidic groups and to render materials with different functional content. This modular approach allows for the convenient preparation of functionalized nanoporous materials from a single block copolymer precursor.