2022 Single Chain Reversible Addition-Fragmentation Chain Transfer (RAFT) Poly(N-isopropylacrylamide) for Chemical Sensing (RAFT) Poly(N-isopropylacrylamide) for Chemical Sensing

Tianyu Ren



University of New Hampshire

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,xxiincreasing 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