Stimuli-responsive amphoteric ion exchange polymers bearing carboxylic and amine groups grafted to a cross-linkable silica network

Stimuli-responsive hybrid organic-inorganic amphoteric ion exchange polymers were synthesizedviaa non-hydrolytic sol–gel process with carboxylic acid and amine groups in silica side chains. Structural characterizationof samples with a ratio carboxylic acid/amine 1:2 (PSU-SiCA(1:2)) and 2:2 (PSU-SiCA(2:2)) showed a degree offunctionalization of 0.5 in both cases. The ion exchange capacity, analysed by acid-base titration, elementalanalysis and thermogravimetric analysis, was 1.8 meq/g for PSU-SiCA(1:2) and 1.2 meq/g for PSU-SiCA(2:2).pH-Dependent properties for acidic, basic and zwitterionic forms were studied including hydration isotherms,ionic conductivity and selective deposition on acidic and basic substrates. The water uptake and ionic con-ductivity of the acidic and basic forms were highest for PSU-SiCA(1:2), due to the higher IEC. The zwitterionicforms, which contain a minimum of mobile ions, showed the lowest water uptake and ionic conductivity. Theacidic form deposited on basic Al2O3substrates and the basic form on acidic SiO2, whereas the zwitterionicpolymer was deposited on neither. The stimulus-dependent ionic conductivity and hydration and the selectivedeposition depending on interfacial charges are striking properties, which make these hybrid bio-friendly io-nomers compelling for applications.