RAFT‐Synthesized Dual Thermo‐Responsive Diblock Copolymer Consisting of Ionic Liquid Polymer: Unveiling Hysteresis and Self‐Aggregation Behavior in Aqueous Solution

This study utilizes the homopolymer, poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate) (PAMPSNa 90 ) to synthesize the thermo‐responsive ionic liquid polymer P[AMPS][P 4448 ] 90 by exchanging the counter cation, sodium (Na + ) of 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) with tributyl(octyl)phosphonium bromide ([P 4448 + ]Br). Furthermore, a two‐step synthesis approach was employed to create a dual thermo‐responsive water‐soluble diblock copolymer PAMPSNa 90 ‐ b ‐PNIPAM 279 composed of PAMPSNa 90 and poly( N ‐isopropylacrylamide) (PNIPAM) via reversible addition‐fragmentation chain transfer polymerization. Later a modification was carried out to exchange the counter cation Na + in PAMPSNa 90 ‐ b ‐PNIPAM 279 with [P 4448 + ], resulting in the P[AMPS][P 4448 ] 90 ‐ b ‐PNIPAM 279 . The individual synthesized polymers were extensively characterized using proton nuclear magnetic resonance spectroscopy and gel permeation chromatography to infer their correct synthesis composition and molecular weight. Turbidity, measured by the percentage transmittance, revealed the thermo‐responsive behavior of these synthesized blocks. The hysteresis phenomenon of heating/cooling for each synthesized polymer was identified as single or dual cloud point temperature, depending on the applied stimuli such as polymer concentration, temperature rate, and sonication. Scattering techniques, such as dynamic light scattering and small‐angle neutron scattering, were employed to obtain insight into the size/shape of the self‐aggregates formed in an aqueous solution environment, which is supported using transmission electron microscopy.