|M.Sc Student||Kulygin Olga|
|Subject||Porous Hydrophilic Polymers Synthesized within High|
Internal Phase Emulsion
|Department||Department of Materials Science and Engineering||Supervisor||PROF. Michael Silverstein|
|Full Thesis text|
A high internal phase emulsion (HIPE) is defined as an emulsion in which the dispersed phase occupies more than 74% of the volume. PolyHIPE are crosslinked porous polymers synthesized by polymerizing monomer in the continuous phase of a HIPE. PolyHIPE have unusual porous structures, low bulk densities and the ability to rapidly absorb large quantities of liquid through capillary forces. These unique qualities seem especially suitable for the development of novel polyHIPE hydrogels. A hydrogel is a polymer network formed by hydrophilic chains which is able to absorb a significant amount of water. A swollen hydrogel contains considerable polymer-free volume that can be used for the nucleation and growth of the nanoparticles.
The objective of this research was to synthesize novel hydrogel polyHIPE and to describe their synthesis-structure-property relationships. One route to hydrogel synthesis was the hydrolysis of polyHIPE copolymers containing vinyl acetate (VAc), divinylbenzene (DVB) and either styrene (S) or 2-ethylhexyl acrylate (EHA). Another route was the synthesis of polyHIPE based on 2hydroxyethyl methacrylate (HEMA) and N,N'-methylenebisacrylamide (MBAM). The molecular structures, morphologies, thermal properties, and mechanical properties of the polyHIPE were characterized. In addition, an attempt was made to modify the polyHIPE through insitu inorganic particle growth.
The porous structures, densities, thermal and mechanical properties and water absorption of the polyHIPE hydrogels were strongly dependant upon the composition and the synthesis process. PolyHIPE copolymers with vinyl acetate were hydrophobic before hydrolysis. After hydrolysis, they absorbed up to 400% of their weight in water and exhibited an increase in compressive Young's modulus and in the tan δ temperature peak. These changes reflect the transformation of acetate to alcohol groups on hydrolysis. The P(HEMA/MBAM) polyHIPE absorbed up to 800% of their weight in water. The tan δ relaxation peak became broader and moved to higher temperatures as the degree of crosslinking increased, reflecting the decrease in segmental mobility. Surprisingly, water absorption is more significant for the polyHIPE with a relatively high degree of crosslinking, reflecting the increase in the surface area and the presence of hydrophilic MBAM units.
The generation of inorganic particles within polyHIPE was also investigated. Several routes were used to generate in-situ inorganic particle growth. The incorporation of metallic salts tended to destabilize the HIPE. Cobalt-based particles were successfully grown within P(S/DVB) polyHIPE.
In summary, in this research porous hydrophilic polymers were successfully synthesized within high internal phase emulsions, and inorganic particles were generated in-situ within the polyHIPE.