RAFT polymerization within high internal phase emulsions: Porous structures, mechanical behaviors, and uptakes

PolyHIPEs are porous, emulsion-templated polymers synthesized within high internal phase emulsions (HIPEs), concentrated emulsions usually containing over 74% of a dispersed internal phase. PolyHIPEs are usually hydrophobic, crosslinked polymers synthesized within water-in-oil (w/o) HIPEs through free radical polymerization (FRP). There have only been a few attempts to use controlled radical polymerizations such as reversible addition–fragmentation chain transfer (RAFT) polymerization for polyHIPE synthesis. Here, the effects of polymerization mechanism, initiator solubility, RAFT agent to initiator ratio, and crosslinking comonomer content upon the porous structure, the static and dynamic mechanical properties, and the swelling of poly(styrene-co-divinylbenzene) polyHIPEs were investigated. The surface-active RAFT agent produced a significant reduction in void size and a significant enhancement in void connectivity. The locus of initiation affected the mechanical behavior, with the moduli from interfacial initiation being significantly higher than those from organic-phase initiation. In addition, using RAFT instead of FRP produced significant changes in the thermal, mechanical, and uptake behaviors that seem to reflect the enhancements in macromolecular mobility and uniformity often associated with controlled polymerization.