|M.Sc Student||Feldman Shirel|
|Subject||Porous Interpenetrating Polymer Networks through|
Oil-in-Water Emulsion Templating
|Department||Department of Materials Science and Engineering||Supervisor||Professor Michael Silverstein|
PolyHIPEs (PHs) are highly porous, emulsion-templated, polymer monoliths polymerized within high internal phase emulsions (HIPEs), emulsions with more than 74 % internal phase. The advantages of PHs include high porosities, low densities, and the ability to absorb relatively large amounts of liquids. Hydrogel (HG) PHs are macroporous, hydrophilic polymers synthesized within oil-in-water (O/W) HIPEs. Interpenetrating polymer networks (IPNs) are formed by simultaneous or sequential synthesis of one polymer network in the presence of another and can be used to tune the macromolecular structure, and thus, achieve synergistic thermal and mechanical properties.
The objective of this research was to develop various IPN HG-PHs where one network is a poly(urethane urea) (PUU) formed through the interfacial step-growth polymerization of pectin and hexamethylene diisocyanate (HDI), and the second network is a HG synthesized using free radical polymerization. The HG monomers were non-ionic (hydroxyethyl methacrylate (HEMA) or acrylamide (AAm)), ionic (acrylic acid (AA) or 2-acrylamido-2-methylpropane sulfonic acid (AMPS)), or zwitterionic (N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethyl-ammonium betaine (SBMA)). The densities, macromolecular structures, porous structures, water uptakes, thermo-mechanical behaviors, and mechanical behaviors of the PHs were characterized. The brittle IPN PH based on SBMA could not be characterized.
Both component networks were present in the IPN PHs, which exhibited open-cell porous structures. P(UU-HEMA), P(UU-AAm), and P(UU-AMPS) seemed to have a broad spectrum of compositions and heterogeneous crosslinked networks, as reflected in their tan δ peaks which were broader than those of the component networks. P(UU-HEMA) and P(UU-AMPS) seemed to have relatively restricted macromolecular mobilities as reflected in their relatively low tan δ peaks. Among the IPNs, P(UU-AMPS) seemed to have the highest macromolecular mobility (the highest tan δ peak). The water uptakes (M) of the non-ionic IPN PHs (P(UU-HEMA) and P(UU-AAm)) did not vary significantly with pH, while the water uptakes increased with pH for the ionic IPN PHs (P(UU-AMPS) and P(UU-AA)), as expected. The water uptakes (M-P) associated with hydrogel swelling in P(UU-AAm) and P(UU-AMPS) were between those of their reference networks, whereas the water uptakes associated with hydrogel swelling in P(UU-HEMA) was less than those of its reference networks. Among the IPN PHs, The water uptakes (both M and M-P) were the highest for P(UU-AMPS) with the most hydrophilic hydrogel (PAMPS) and the lowest for P(UU-HEMA) with the least hydrophilic hydrogel (PHEMA). Among the IPN PHs, the higher the tan δ peak, the greater the decrease in the mechanical properties, E and σ70, upon hydration. Both may reflect the highly hygroscopic nature of PAMPS.
Interconnected polymer networks (ICNs), two networks with covalent connections, seemed to be formed in P(UU-AMPS) and P(UU-AA) from possible reactions between the sulfonic acid and carboxylic acid groups, respectively, with HDI, with P(UU-AMPS) exhibiting two tan δ peaks and P(UU-AA) exhibiting an unexpected, relatively homogeneous structure, as reflected in its relatively narrow tan δ peak compared to that of the PAA reference.