|M.Sc Student||Warwar Damouny Christine|
|Subject||Hydrogel-Filled Porous Shape Memory Polymers from Long|
Side-Chain Monomers via Emulsion Templating
|Department||Department of Materials Science and Engineering||Supervisor||Professor Michael Silverstein|
|Full Thesis text|
PolyHIPEs are porous polymer systems based on high internal phase emulsions (HIPEs). Semi-crystalline polyHIPEs can exhibit shape memory behavior based upon reversible crystallization within a crosslinked polyHIPE. Such polyHIPEs were synthesized within Pickering HIPEs; HIPEs stabilized using amphiphilic silane-modified silica nanoparticles (NPs) that also acted as crosslinking centers through the reaction of the growing macromolecules with methacryloxy groups on the NP surfaces. Temporary shapes could be imposed on polyHIPE shape memory polymers (SMPs) by heating above the melting point (Tm), deforming, and cooling under imposed deformation. The original shapes could be recovered with high recovery ratios by heating above the Tm. Filling the polyHIPE SMPs with hydrogels (HGs) could be used to produce porous SMPs that would respond rapidly in aqueous environments. The objectives of this research were to synthesize hydrogel-filled water-sensitive porous SMPs based on crystallizable long side-chain monomers and to investigate their behavior. To this end, the influence of the synthesis parameters (the stabilization method, the locus of initiation, the degree of crosslinking, the nature of the hydrogel, and the length of acrylate side-chain) on the macromolecular structure, on the porous morphology, on the crosslinked network structure, on the mechanical and thermal properties, and on the shape memory behavior were investigated.
The nature of the hydrogel was found to significantly affect the porous structures of polyHIPEs based on stearyl acrylate (A18). A hydroxyethyl methacrylate-filled polyHIPE from a surfactant-stabilized HIPE exhibited a fixity ratio of 95% and a recovery ratio in air of 97%, but with a recovery rate that was significantly slower than that of the equivalent unfilled polyHIPE. Other hydrogel-filled polyHIPEs from surfactant-stabilized HIPE exhibit poor shape memory behavior. For the unfilled polyHIPEs from a Pickering HIPEs, the fixity ratio was 100%, and there was a rapid two-stage recovery of 95% in air. The presence of dehydrated hydrogels in the polyHIPEs from Pickering HIPEs increased the modulus but, in general, resulted in poor shape recovery behavior. On the other hand, the recovery of the hydrated HG-filled polyHIPEs in water was superior to that of the hydrophobic unfilled polyHIPE. Interfacial initiated polyHIPEs from Pickering HIPEs that were based on stearyl and behenyl acrylate (A22), exhibited spherical polymer protuberances with a thread-like texture that seemed to exude from the walls. A22-based polyHIPEs exhibited fixity ratios of 100% and exhibited two-stage recoveries of 90% which were influenced by the programming temperature.