Hierarchical porosity in emulsion-templated triblock copolymer-like structures: Mid-block degradation and end-block hypercrosslinking

Hierarchically porous structures can enhance the applicative performance of porous polymers. Macroporous polymer monoliths (polyHIPEs) can be generated by templating within high internal phase emulsions (HIPEs) and mesoporous polymers can be generated through block copolymer (BCP) templating. Here, novel hierarchically porous polymer monoliths were generated by emulsion templating BCP-like macromolecular structures consisting of a sacrificial poly(ε-caprolactone) (PCL) mid-block and hypercrosslinkable poly(styrene-co-divinylbenzene) (P(S-co-DVB)) end-blocks synthesized from a PCL macroinitiator using activators generated by electron transfer for atom transfer radical polymerization. The macroporous structures were networks of sub-micrometer channels. Hierarchical porosities were generated by etching the PCL and/or by hypercrosslinking the P(S-co-DVB). Etching removed ∼40 % of the PCL, generating mesoporosity. Hypercrosslinking generated both microporosity and mesoporosity, with a specific surface area of ca. 800 m²/g for 50 wt % P(S-co-DVB). Unexpectedly, hypercrosslinking the etched polyHIPE yielded less microporosity and mesoporosity, indicating that the PCL was integral to the mechanism of pore generation. This work serves as the foundation of an approach to generating innovative hierarchical porosities in polyHIPEs that can be pre-designed through the synthesis of BCPs followed by post-synthesis modifications.