Nanoporous Polymer Films via the Self-Assembly of Triblock Copolymers

Diblock copolymer films of polystyrene-$b$-poly(ethylene oxide) (PS-PEO) exhibiting cylindrical microdomains, where PS is the major component, demonstrate a high degree of long range lateral order by solvent casting or solvent annealing. However, to generate nanoporous films of these materials we have incorporated a third, center block that is photodegradable by ultra violet radiation. This provides for a robust route to generating highly ordered, nanoporous arrays polymer films. Triblock copolymers of polystyrene-$b$-poly(methyl methacrylate)-$b$-poly(ethylene oxide) (PS-PMMA-PEO) were synthesized by ATRP. Three different molecular weights and compositions were used, where PS is the major component, and PMMA and PEO are the minor components. After casting and solvent annealing, all three copolymers exhibit similar cylindrical microdomains. Subsequently, PMMA block can be UV degraded and by rinsing in acetic acid and water, only the PS block remains in the nanoporous films.