pH- and Thermo-responsive Polymer Assemblies in Aqueous Solution

摘要

Responsive polymers were prepared by copoly merizing a small amount of ionizable monomers, acrylic acid or N,N-dimethylarninopropylmethacrylamide, with N-isopropylacrylamide (NIPA) and the solubility in aqueous solution of these PNIPA derivatives were quantitatively studied. From differential scanning calorimetry experiments, it was shown that the pH strongly influences the phase separation of these copolymers (temperature and enthalpy), which totally disappears when ionizable groups are fully charged. At pH 7, all PNIPA copolymers remain soluble in water at all temperatures but their mixtures show a phase separation above a critical temperature due to the formation of a reversible inter-polyelectrolyte complex. When the responsive stickers are grafted on a poly(acrylamide) back bone, pH and temperature are still able to drive the associa tion process at a local scale, giving rise to a sol/gel transition of semi-dilute solutions. The structure and the viscoelastic properties of these macromolecular assemblies are investi gated by small angle neutron scattering and rheology and their responsivity is discussed as a function of pH and temperature.