Nanoporous Materials Formed in Condensed Carbon Dioxide

We propose a strategy utilizing condensed carbon dioxide as a selective--solvent for creating nanoporous materials from block copolymer templates. Cylinder--forming polystyrene--$b$--polylactide ($f_{PLA}$ = 0.37) monoliths were annealed in carbon dioxide at constant temperature and various solvent densities. The swollen structures were then quenched at low temperature isochorically. Small-angle X-ray scattering measurements indicated the domain spacing increased with increasing CO$_{2}$ density. This result is consistent with the formation of cylindrical pores within the intact polylactide domains, a conclusion confirmed by scanning electron micrographs of the processed monoliths. This controlled, non-destructive technique allows for creating tunable pore structures from a single block copolymer.