Date of Award
Program or Major
Doctor of Philosophy
W. Rudolf Seitz
An approach to single chain poly-N-isopropyl acrylamide (polyNIPAM) with a redox tag was polymerized by the reversible addition fragmentation-chain transfer (RAFT) method. Molecularly imprinted polymers (MIPs) technology is the design of an artificial receptor with high selectivity for a specific analyte. The synthesized RAFT polymers were devised to develop conformation-based electrochemical MIP sensors.The material polyNIPAM is attractive as a receptor of a chemical sensor. Due to its thermosensitive properties, polyNIPAM collapses above the lower critical solution temperature (LCST) and returns to its original state when the temperature is reduced below LCST. This reversible aggregation behavior shows that polyNIPAM has a flexible structure vital to generating a conformational change with stimulus and molecular recognition. Beyond the aggregation behaviors, the isopropyl group of these monomers can form hydrophobic interactions, which helps create non-covalent interactions, the same as the use of acidic and basic functional monomers in MIP synthesis. This non-covalent crosslinking can reduce the number of covalent crosslinkers, increasing the binding affinity of the MIPs. Another approach to minimize binding blockage and increase the binding affinity is untangling in THF, which takes approximately one day to reach an equilibrium state. The polyNIPAM size measurements by dynamic light scattering (DLS) were conducted because it confirmed that the reversible aggregation behavior of polyNIPAM was not influenced by an applied voltage. The success of synthesis and characterization of ferrocene contained polyNIPAM illustrates that modifying a redox tag on the RAFT agent is feasible. However, ferrocene was found to not be stable with vinyl-pyridine, which is the basic functional monomer used in the current MIP recipe. Due to this, exploration of other redox tags such as triphenylamine (TPA) and anthraquinone (AQ) were tested. These redox tags were found not to be adequate for our application. As a result, they were declared to no longer be candidates for the project. However, methylene blue (MB), another redox tag option, was studied. It is believed that MB has the potential to make this approach of conformational-based electrochemical MIP sensors work, but it will require more research. For this reason, future work should focus on this redox tag.
Ren, Tianyu, "Single Chain Reversible Addition-Fragmentation Chain Transfer (RAFT) Poly(N-isopropylacrylamide) for Chemical Sensing" (2022). Doctoral Dissertations. 2704.