Temperature and oxidation-responsive nanomicelle based on polyethyleneimine and (phenylthio)acrylic acid

Polyethyleneimine (PEI), a cationic hydrophilic polymer, and (phenylthio)acrylic acid (PTAA), a hydrophobic counter ion, were used to prepare ion pair self-assembly (IPSAM), which is sensitive to temperature and oxidation. The IPSAM was spontaneously formed when the amino group to carboxylic group molar ratio was 5/5 to 7/3. On the TEM micrograph, PEI/PTAA IPSAM was discovered as sphere-shaped nanoparticles with a diameter of tens of nanometers. The upper critical solution temperature (UCST) of the ion pair increased as the PTAA content increased and decreased when H₂O₂ oxidized the PTAA of the ion pair. The ion pair was interface active due to its amphiphilic property and the interface activity was decreased upon the PTAA oxidation. FT-IR and ¹H NMR spectroscopy were used to verify the ionic interaction among PEI and PTAA, and X-ray photoelectron microscopy was used to confirm the oxidation of PTAA. The release of a payload (i.e. Nile red) in IPSAM was limited when the medium temperature was lower than the UCST but it was triggered above the phase transition temperature possibly due to the disintegration of the IPSAM. Upon oxidation, the UCST would decrease below the release medium temperature due to the PTAA oxidation causing promoted release and the release degree could occur readily in proportion to the H₂O₂ concentration.

Schematic diagram of temperature and oxidation-responsive of PEI/PTAA self-assembly ion pairs (IPSAM)