Thermo-, pH-, and Light-Responsive Supramolecular Complexes Based on a Thermoresponsive Hyperbranched Polymer.

Hyperbranched polyethylenimine terminated with isobutyramide groups (HPEI-IBAm) was mixed with 4-(phenylazo)benzoic acid (PABA) to form supramolecular complexes through the neutralization reaction between the amino groups of HPEI-IBAm and the carboxylic acid group of PABA, which was verified by H and 2D NOESY H NMR spectroscopy. The obtained supramolecular complexes with a molar ratio of PABA to HPEI-IBAm of ≤8 were soluble in water and exhibited thermoresponsive properties. Their cloud point temperature () was sensitive to PABA content, and PABA molecules were exchanged between HPEI-IBAm hosts. The topology of the polymer affected the change in of the complexes. At pH ∼7, increasing the PABA content decreased , whereas it caused to increase at pH ∼9. Reversible -to- photoisomerization of azobenzene units in the complexes occurred following irradiation with UV or visible light. At pH ∼7, -to- isomerization of azobenzene units increased , whereas the opposite occurred at pH ∼9.