pH-sensitive multilayers based on maleic acid terpolymers with weak and strong acid moieties

Multilayer films were assembled from a maleic acid terpolymer, poly[(maleic acid-alt-styrene)-co-2-acrylamido-2-methyl-1-propansulfonic acid], deposited in alternation with weak polycations: poly(allylamine hydrochloride) or chitosan. The strong acid groups of the terpolymer assured the films stability by electrostatic linkages, and the weak carboxylic groups from the maleic acid assured the pH-responsiveness to external pH changes. In order to study the influence of the ratio between the weak and the strong acid groups of the polyanion on the multilayer properties, two maleic acid terpolymers were synthesized and characterized by potentiometric titration, FTIR and 1H NMR spectroscopy. The influence of the assembling pH and of the nature of the polycation on the multilayer properties was investigated. The pH-sensitivity of the obtained films was demonstrated by loading and release studies of a model cationic dye: Rhodamine 6G. The amount of the cationic dye incorporated into the films increased with the increase of the pH of the post-treatment solution, but was also very much influenced by the assembling conditions. A high ratio between the weak and the strong acid groups of the maleic terpolymer and an acidic pH deposition were needed to assure a high loading capacity of the multilayers. The dye release profiles were also pH-dependent due to the variation of the anionic charges of the maleic acid terpolymer from the films.