Designing an Emulsion-Templated Pentablock Copolymer for Hierarchical Porosity

Hierarchically porous polymers integrate macro-, meso-, and micropores to enhance mass transport, diffusion, and specific surface area, making them attractive for applications in filtration, separation, and storage. Here, an innovative pentablock copolymer (PBC), synthesized using sequential atom transfer radical polymerizations (ATRPs), was designed so that each block would contribute a distinct level of porosity to a hierarchically porous monolith. First, a triblock copolymer with hyper-cross-linkable polystyrene (PS) end-blocks was synthesized from a macroinitiator based on a degradable polycaprolactone (PCL) diol. The PBC was then synthesized by adding cross-linkable poly(glycidyl methacrylate) (PGMA) end-blocks to the PS-b-PCL-b-PS. The PBC was used to form the external phase of an oil-in-oil medium internal phase emulsion and then cross-linked via the PGMA's epoxide groups to generate a macroporous monolith. Selectively etching the sacrificial PCL midblocks in the emulsion-templated monolith generated mesopores. Hyper-cross-linking the PS blocks generated micropores and etched some of the PCL, generating mesopores. This multiblock pore-generation strategy enabled control over the hierarchical nature of the porous structure, providing a rational approach to designing robust, tunable porous monoliths for advanced applications.