|M.Sc Student||Cohen Samoocha Dikla|
|Subject||Bicontinuous Hydrogel-Filled Hydrophobic Polymers|
Synthesized within Polymer-Nanoparticle-Stabilized
|Department||Department of Materials Science and Engineering||Supervisor||Professor Michael Silverstein|
|Full Thesis text|
This work describes the incorporation of hydrogels (HGs) into crosslinked porous polymers, termed polyHIPEs, synthesized within polymer -nanoparticle-stabilized high internal phase emulsions (HIPEs). Relatively large amounts of expensive surfactants are usually needed for HIPE stabilization and then, following polymerization, they are difficult and costly to remove. Therefore, replacing the surfactants in HIPEs should prove highly advantageous. Pickering emulsions are stabilized through the spontaneous assembly of amphiphilic particles at the oil-water interface, rather than through the use of organic surfactants. Hydrogels are hydrophilic polymer networks which can absorb up to a thousand times their dry weight in water and are used for controlled release systems. Previous work has shown that hydrogels can be incorporated into polyHIPEs. The advantages of hydrogels include the easy loading and release of water-soluble bioactive macromolecules and the ability to manipulate the release rate through control of hydrogel swelling. Bicontinuous, hydrogel-filled, rigid, polystyrene-based polyHIPEs from surfactant-stabilized HIPEs have recently exhibited potential as release systems.
The objectives of this work were to synthesize such bicontinuous polyHIPEs within nanoparticle-stabilized HIPEs, to characterize the structures and properties of the resulting polyHIPEs, and to evaluate their behavior as release system. In this work, crosslinked amphiphilic polymer nanoparticles (PNPs) synthesized through the emulsion copolymerization of styrene (St), divinylbenzene (DVB), and maleic anhydride (MA) were used to stabilize HIPEs for polyHIPE synthesis. The hydrophobic monomers in the HIPE's external, organic phase were 2-ethylhexyl acrylate (EHA) and DVB and the hydrophilic monomers in the HIPE's internal, aqueous phase were acrylamide (AAm) and N,N ' -methylenbisacrylamide (MBAM). The type and amount of PNPs had significant effects upon the porous architecture. The porous structure and the location of the PNPs in the polyHIPEs were strongly affected by the locus of initiation (in the organic phase, at the interface, or both). PolyHIPEs were also successfully synthesized using: (i) PNPs that both stabilized the HIPE and initiated the polymerization; (ii) PNPs that both stabilized the HIPE and crosslinked the polymer (replacing the crosslinking comonomer); (iii) PNPs that preformed all three functions. While the hydrogel covered the interconnecting holes in the HG-filled PEHA-based polyHIPEs, the structure was still open and water could be removed and reabsorbed. The mechanical properties of these polyHIPEs were affected by the type of initiation, the type of crosslinking, the presence of a hydrogel, and the state of the hydrogel (hydrated or dehydrated). The glassy, dried hydrogel significantly enhanced the polyHIPE modulus while the hydrated hydrogel did not affect the modulus. The polyHIPEs with no hydrogel were hydrophobic and exhibited poor water absorption, while the hydrogel-filled polyHIPEs exhibited significant water absorption. The uptake and release from the elastomeric hydrogel-filled polyHIPEs were relatively slow, reflecting the closed-cell-like porous structures.
This work demonstrated that novel families of emulsion-templated porous polymers could synthesized using PNP-stabilized HIPEs. The PNPs’ ability to stabilize the HIPEs, to initiate polymerization, and to crosslink the polymer is an important step forward in the development of emulsion-templated polymer systems.