Nanoporous polystyrene monoliths were prepared from polystyrene-polylactide (PS-PLA) block copolymers that form hexagonally packed nanocylinders of PLA in a PS matrix. A morphology diagram was developed to determine the range in composition and molecular weight over which this morphology existed. Macroscopic alignment of these materials gave anisotropic monoliths that were subjected to mild degradation conditions leading to the chemical etching of the PLA. The resulting nanoporous monoliths consisted of a polystyrene matrix containing hexagonally close-packed, oriented, and continuous nanoscopic channels (pore size was tunable through synthesis or blending) lined with chemically accessible hydroxyl functional groups. Both the precursors and the porous materials were analyzed moleculary (size-exclusion chromatography and proton nuclear magnetic resonance spectroscopy) and structurally (small-angle X-ray scattering, scanning electron microscopy, and differential scanning calorimetry). In addition, the surface area and pore size distribution of the nanoporous monoliths were characterized (N2 adsorption measurements). These nanoporous materials have remarkable potential as hosts for nanomaterial synthesis, size-selective catalyst supports, and advanced separations.

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Block copolymer thin films are ideal templates for a wide range of technologies where large area patterns of nanoscale features are desired. One of the main challenges in using lamellae-and cylinderforming block copolymers for this purpose is to induce the block copolymer domains to orient perpendicular to the film surface. We here show that perpendicular domain orientation can be easily achieved with polystyrene-b-polylactide (PS-PLA) thin films. Cylinder-forming PS-PLA films were prepared by spincoating on a variety of substrates followed by thermal annealing. The molecular weight, film thickness, annealing temperature, and annealing time were varied. When the film thickness was larger than the repeat spacing of the bulk morphology, the domains oriented perpendicular to the surface independent of the substrate/film interface. The films were then used to prepare nanoporous templates by a combination of hydrolytic PLA degradation and oxygen reactive ion etching (O 2-RIE). The template pattern was then transferred to the substrate using CF4-RIE to form an array of nanoscale pits.

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