Highly efficient and tunable miktoarm stars for HIPE stabilization and polyHIPE synthesis

Abstract PolyHIPEs, macroporous polymers synthesized within the external phases of high internal phase emulsions (HIPEs), have been developed for a wide range of applications (catalyst supports, tissue engineering, drug delivery) in which the leaching of traditional surfactants can become a significant liability. HIPEs can also be stabilized with relatively small amounts of amphiphilic solid nanoparticles, as well as with miktoarm stars, poly(divinylbenzene) (PDVB) cores bearing different types of polymer arms. In this paper, two types of stars bearing both poly(ethylene oxide) and polyacrylate arms were used to stabilize HIPEs, non-reactive stars and stars bearing reactive methacrylate groups. The 0.1 wt % of stars successfully used to stabilize HIPEs containing styrene and DVB were not enough, at low DVB contents in the HIPE, to provide the crosslinking support needed to resist the capillary stresses generated during drying. However, with sufficient DVB in the HIPE, star contents as low as 0.05 wt % were able to successfully stabilize a HIPE with 90% internal phase and produce a polyHIPE with a density of 0.06 g/cm3. As little as 0.07 wt % stars were enough to stabilize HIPEs containing long side-chain (meth)acrylates and ~0.7 wt % of a crosslinking polyhedral silsesquioxane (POSS) and yield polyHIPEs with densities of around 0.2 g/cm3. These polyHIPEs exhibited rapid shape recovery and recovery ratios of 100% when a temporary shape (a 70% compressive strain) was imposed above the melting point of the crystalline phase. Star stabilization combined with POSS crosslinking enable the generation of tunable shape memory polymer foams.