Preparation And Characterization Of Multistimuli-responsive Supra-molecular Complexes

In this article, a kind of thermoresponsive polymer with a certain degree ofsubstitution was prepared from HPEI after amidation of butyl anhydride (IBAm).Hyperbranched polyethylenimine terminated with isobutyramide groups(HPEI-IBAm) was mixed with4-(phenylazo) benzoic acid (PABA) to formsupramolecular complexes through the neutralization reaction between the aminogroups of HPEI-IBAm and the carboxylic acid group of PABA, which was verifiedby1H and2D NOESY1HNMR spectroscopy. Also, some facts about temperature,pH, and light have been made detailed studies. The obtained supramolecularcomplexes with a molar ratio of PABA to HPEI-IBAm of≤8were soluble in waterand exhibited thermoresponsive properties. Their cloud point temperature (Tcp) wassensitive to PABA content, and PABA molecules were exchanged betweenHPEI-IBAm hosts. The comparison between supramolecular complexes which wasprepared by linear polymers and hyperbranched supramolecular complexes provedthat the topology of the polymer affected the change in Tcpof the complexes. Theresponsiveness of hyperbranched supramolecular complexes to pH: At pH～7,increasing the PABA content decreased Tcp, whereas it caused Tcpto increase atpH～9.The responsiveness of hyperbranched supramolecular complexes to light:Reversible trans-to-cis photoisomerization of azobenzene units in the complexesoccurred following irradiation with UV or visible light. At pH～7, trans-to-cisisomerization of azobenzene units increased Tcp, whereas the opposite occurred atpH～9.