THERMODYNAMICS OF MULTIPLE STIMULI-RESPONSIVE POLYELECTROLYTES WITH COMPLEXING ABILITY TOWARDS THE COPPER(II) ION

The thermodynamics of protonation of carboxylate groups in polymers co ntaining amido and isopropyl moieties was studied in 0.1 M NaCl at dif ferent temperatures. Compared with polymers with the L-leucine moiety, poly(N-acryloyl-L-valine) showed a wider decreasing linearity of the basicity constant (log K) in relation to the degree of protonation (al pha), with a minimum at alpha = 0.65. Under these conditions, a sharp endothermic peak revealed the presence of hydrophobic interactions as the macromolecule assumed a compact coil conformation and water molecu les were released with an increase in entropy. The graft polymers on t he surface of a polyurethane film displayed larger potentiometric hyst eresis loops with respect to the cellulose support, as the nature of t he polymer was similar to that of the hydrophobic substrate. The rever sible configuration of the graft polymer chains instantly responded to changes in pH and temperature, modifying the rate of water filtration through the membrane pores. As the temperature approached 31 degrees C an abrupt increase in water permeation was observed even though the graft polymer was in the uncharged and coiled state. The polyelectroly te formed a hydroxo-complex species, involving two monomer units (L(-) ) of the polymer, with the Cu(II) ion. Electron paramagnetic resonance (EPR) spectra, supported by conductometric data, revealed Cu(OH)(2)L( 2)(2-) stoichiometry in solution. The potentiometric data showed a goo d fit when processed by the Superfit program and a decreasing pattern of log beta in relation to pH.