Poly(acrylamide-co-styrene): A Macrosurfactant for Oil/Water Emulsion Templating toward Robust Macroporous Hydrogels

Abstract

Large amounts of relatively expensive small-molecule surfactants, between 6 and 25%, are typically required for the formulation of oil/water high or medium internal phase emulsion (H/MIPE) templates. We synthesized an amphiphilic “macrosurfactant” copolymer poly­(acrylamide-co-styrene) via micellar polymerization. As-synthesized poly­(acrylamide-co-styrene) still associated with 0.01 wt % cetyltrimethyl­ammonium bromide (CTAB) can be used to produce stable toluene or cyclohexane-in-water H/MIPEs already at concentrations of 0.1 wt %. Emulsion templates containing 2-hydroxyethyl methacrylate (HEMA) and N,N-methylene­bis­(acrylamide) (MBAm) in the aqueous continuous phase can be polymerized to produce macroporous poly­(HEMA-co-MBAm)­M/HIPEs. Our poly­(HEMA-co-MBAm)­M/HIPEs synthesized in templates stabilized with much lower emulsifier content were mechanically more robust, in dry and swollen state, as compared with poly­(HEMA-co-MBAm)­HIPEs reported in the literature.

Polydimethylsiloxane Polymerized Emulsions for Acoustic Materials Prepared Using Reactive Triblock Copolymer Surfactants

“…We hypothesize that the increase in G ′ is due to a strengthening of the pore walls due to the reactive surfactant participating in the thiol–ene reactions localized at the pore wall occurring during the CP during polymerization. Recent work by Bismarck, Jiang, and co-workers also showed that using polymeric surfactants resulted in an increase in compressive moduli compared to small molecule surfactants, and they attributed this to the polymeric surfactant strengthening the pore wall struts by becoming entangled within the polymer network, rather than cross-linked into the network as is the case in our work. Debuigne and co-workers also reported that covalently bonding CTA-terminated RAFT surfactants to the walls of a polyHIPE resulted in polyHIPEs with higher mechanical properties due to differences in the interconnectivity of the pores compared to polyHIPEs using surfactants that were physically anchored or not anchored at all.…”

“…Alternatively, open-cell pore structures can be obtained by using polymeric surfactants and by initiating the polymerization from the CP. Furthermore, tuning of the pore structure has been achieved using block copolymer surfactants with different ratios of hydrophilic to hydrophobic character. , One method to prepare amphiphilic block copolymer surfactants is reversible addition–fragmentation chain transfer (RAFT) polymerizations, , and this method has been used to prepare surfactants for HIPE stabilization. − For example, Debuigne and co-workers synthesized a library of poly­(ethylene oxide)/polystyrene (PEO/PS) block copolymers with different PS contents using RAFT polymerizations to prepare PS/DVB-based polyHIPEs with different degrees of openness. In that work, it was shown that PEO/PS surfactants with equal block ratios obtained the highest degree of openness of ∼10%, and surfactants with the highest PS content obtained the lowest degree of openness of ∼2%.…”

“…Polymeric surfactants change the properties of polyHIPEs’ pore surfaces by introducing functionality into the polyHIPE surface from the surfactant. ,− When these types of surfactants are integrated into the polymer network through physical anchoring or chemical reactions during the polymerization of the CP of the polyHIPE, they are called “reactive” surfactants. Reactive surfactants have been used to limit surfactant leaching or introduce hydrophilicity to a hydrophobic polymer surface in a one-step process, and they have recently been shown to improve the compressive mechanical properties of polyHIPEs compared to small-molecule surfactants …”

Mechanism of Interconnected Pore Formation in High Internal Phase Emulsion-Templated Polymer

“…High internal phase emulsion (HIPE), an emulsion containing internal phase of >74% dispersed as individual droplets, has been known for many years and has found applications in fields such as food, fuels, oil recovery, biphasic interfacial catalysis, and cosmetics. − In the past 20 years, a growing interest focuses on its application in materials science, i.e., as template to fabricate highly porous structure (so-called HIPE-templating technique). ,− HIPE is commonly stabilized by high content of nonionic surfactant (5–50%, relative to its continuous phase) owing to its high volume ratio of disperse phase/continuous phase. − When the HIPE contains monomers in its continuous phase, polymerization of the monomers and removal of the dispersed phase could cause a highly open-cell foam, named polyHIPE. − The HIPE-templating technique provides the advantages of generating porous materials with a diverse morphology, for example, polymer foams, membranes, beads, or rods. Since the structure of polyHIPE replicates from its precursor HIPE-template, by tuning the droplet size and the chemical nature of HIPE phases, polyHIPEs with designed performance can be fabricated. − Moreover, in situ or postpolymerization approaches can be also adapted to tune the surface area or endow polyHIPE with additional chemical properties. − PolyHIPEs could be used in a wide range of areas, including energy storage applications, , tissue engineering, chromatography, separation, , microreactors, , sound absorption, , and catalysis. − The implementation of these applications largely depends on their highly open-cellular structure, i.e., the presence of interconnected pores (also named pore throats or windows) between adjacent voids.…”