Multi‐Length Scale Porous Polymers

Abstract

Thin films with porosities spanning from the nanoscopic to the macroscopic are obtained by combining breath figures (BFs), micrometer‐sized surface cavities arising from the condensation of water on the surface of a film as solvent evaporates rapidly, with the nanoscopic morphology inherent to block copolymers. Using chloroform as a solvent for polystyrene‐b‐poly methyl methacrylate (PS‐b‐PMMA) block copolymers (BCPs), micrometer‐sized pores arise from the formation of the BFs, while nanoscopic pores are generated by the removal of the PMMA by deep UV‐irradiation, which also crosslinks the PS. Solvent retention, though, limits its utility. This is overcome using PS‐b‐poly(n‐butyl methacrylate) dissolved in dichloromethane where, again, multi‐length scales of porosity are achieved by a selective removal of one component of BCPs. Arrays of nanopores on the surface of a film can also be obtained by swelling the hydrophilic component block of PS‐b‐poly(ethyleneoxide) (PEO) with water vapor, under controlled humidity. Simultaneously, large pores can be obtained by macrophase separation between BCPs and water, which leads to multi‐length scale porous films.