Development of Smart Hydrogel Oscillators

Abstract

The palladium-catalysed oxidative carbonylation reaction, named the BT-GN reaction, after the core contributors Bruk, Temkin, Gorodsky and Novakovic has garnered attention due to its ability to produce oscillations in pH, redox potential, turbidity, and heat of the reaction. It is an organic oscillatory reaction taking place under lab conditions where complex products are formed from simple starting materials. The BT-GN reaction has attracted interest for use as a driving force for smart materials such as pH-responsive hydrogels. To achieve this oscillatory potential, the BT-GN reaction must be adapted to produce oscillations in pH within a polymeric framework. The majority of studies of BT-GN report phenylacetylene as a substrate and palladium iodide as a catalyst, which requires replacing polymeric analogues. A more recent effort by the Novakovic group offered evidence of other palladium catalysts and a polymeric alkyne-based substrate (poly(ethylene glycol) methyl ether acetylene, PEGA) also producing oscillation in pH. Furthermore, a proof-of-concept study demonstrated self-oscillating chitosan macrogel with phenylacetylene as a substrate. This thesis covers a detailed study into oscillatory BT-GN reactions between polymeric catalysts such as chitosan-2-pyridylimine palladium chloride (Chi-IM-PdCl2) and polymeric substrate (PEGA) both in solution and in hydrogels to aid in the development of a functional self-oscillating hydrogel that can swell and collapse in volume. This is possible thanks to hydrogels having the ability to swell and collapse due to pH stimulation that encourages the movement of fluids both into and outside of the gel depending on pH. Key findings of this thesis include differences in oscillatory behaviour between methanol and ethanol in Chi-IM-PdCl2 catalysed BT-GN reactions with phenylacetylene. Oscillations between PEGA and Chi-IM-PdCl2 in BT-GN reactions. The effects of KI on the BT-GN reaction and how using recycled Chi-IM-PdCl2 increased the duration of oscillations.