Supramolecular control over pH- and temperature-responsive dialkoxynaphthalene-functionalized poly(2-(dimethylamino)ethyl methacrylate) in water

Abstract

Abstract In the framework of the development of multi-responsive polymer materials, a well-defined copolymer bearing supramolecular recognition units was designed based on 2-(dimethylamino)ethyl methacrylate (DMAEMA) and a dialkoxynaphthalene-functionalized monomer (NaphtA). The supramolecular host-guest interactions of this P(DMAEMA-co-NaphtA) copolymer with the electron-deficient CBPQT4+, 4 Cl- cyclophane host were studied by 1H NMR spectroscopy, UV-Visible spectroscopy and isothermal titration calorimetry (ITC), revealing, a high association constant of 6.5×105 M-1 in water. The addition of CBPQT4+, 4 Cl- to a colorless solution of the copolymer in water resulted in a purple solution due to the formation of donor-acceptor inclusion complexes, the intensity being directly proportional to the amount of host added. Investigations on the thermoresponsive behavior of the naphthalene-functionalized copolymer highlighted that the cloud point temperature is directly proportional to the amount of CBPQT4+, 4 Cl- host added and can simply be programmed within a temperature window from 30 °C to 48 °C by playing with pH. The dethreading process was studied as function of temperature and anionic exchange of the counterions of the CBPQT4+, 4Cl-. Interestingly, a partial decomplexation was observed by heating the sample above the cloud point temperature while a complete and programmable dethreading was achieved by adding the anionic surfactant sodium dodecyl sulfate (SDS) as a competitive counterion of the host molecule.