|M.Sc Student||Horowitz Rotem|
|Subject||Porous Shape-Memory Polymers Synthesized Through Emulsion|
|Department||Department of Materials Science and Engineering||Supervisor||PROF. Michael Silverstein|
|Full Thesis text|
PolyHIPEs, porous polymers with open-cell, highly interconnected pore structures are synthesized through templating within high internal phase emulsions (HIPEs), emulsions in which the internal phase occupies more than 74% of the volume. The porous structure and properties can be tailored by adjusting the HIPE composition and by modifying various synthesis parameters. PolyHIPEs synthesized within Pickering HIPEs are stabilized using nanoparticles (NPs) that can also function as centers of crosslinking and initiation. Previously, shape memory polyHIPEs (SMPHs) were synthesized using acrylate or methacrylate monomers bearing long, crystallizable, aliphatic side-chains. A temporary shape, imparted above the crystalline melt transition (Tm), was “locked in” upon quenching below the Tm. Shape memory behavior was produced by the crosslinked network returning to the original shape upon “unlocking” above the Tm. The use of HIPE-stabilizing, polymer crosslinking, surface-modified silica NPs was critical to achieving SMPHs. Instead of using silica NPs, recent work has shown another way for stabilizing Pickering emulsions, and HIPEs in particular, is using Miktoarm stars. Miktoarm stars, amphiphilic block copolymers that contain a water-soluble hydrophilic block and water-insoluble hydrophobic block, have been used to stabilize emulsions. Star polymers are highly efficient stabilizer and only a relatively low concentration is needed to stabilize HIPEs.
The objectives of this research were to develop novel families of SMPHs and to enhance the shape memory effect by varying the crystallizable monomer, the emulsification strategy (NPs, surfactant, Miktoarm stars) and the crosslinking strategy (NP type, NP location). These variations were expected to affect the macromolecular structure, the porous morphology, the crosslinked network, the mechanical and thermal properties, and the shape memory behavior. The influence of a polyhedral oligomeric silsesquioxane (POSS) as a comonomer for enhancing the shape memory behavior and as a crosslinker was investigated.
PolyHIPEs were successfully synthesized from acrylates and methacrylates with aliphatic side-chain lengths of 18 and 22. Three different systems were synthesized successfully by using three different stabilizing strategies: NPs, a surfactant, and stars. The porous structures were, for the most part, similar to those of typical SMPHs and the densities ranged from 0.13 to 0.20 g/cc. Shape memory behavior was enhanced using POSS as an additional crosslinker in NP-stabilized HIPEs. Novel families of SMPHs were achieved by using POSS as a crosslinker in a star-stabilized HIPEs. Shape recovery ratios of 100% were achieved, which are higher than those achieved in previous work.