Synthesis, characterisation and properties of alfa,beta-poly(N-2-hydroxyethyl)-DL-aspartamide-graft-maleic anhydride precursors and their stimuli-responsive hydrogels.

A family of poly(amino acid)-maleic anhydride hydrogels were designed and synthesized. Water soluble polymeric precursors were prepared by partially substituting the hydroxyl groups of the alfa,beta-poly(N-2-hydroxyethyl)-DL-aspartamide backbone with maleic anhydride, so as to provide double bonds for crosslinkingand carboxylic acid groups for pH and electric field responsiveness. Reaction conditions (reactivemixture composition and catalysis) were systematically varied in order to obtain PHEA–MA precursorswith different and reliable graft-maleic anhydride levels. PHEA–MA precursors were characterised bytitration, Nuclear Magnetic Resonance (1H NMR), Fourier-Transformed Infrared Spectroscopy (FTIR)and Size Exclusion Chromatography (SEC) for structural and molecular determination. Aqueous solutionsof selected PHEA–MA precursors were subjected to gamma-irradiation at different irradiation doses andpolymer to water concentrations in order to induce chemical crosslinking without the addition of crosslinkingagents. The yield of crosslinking reactions was evaluated by solubility tests as well as the effect ofammonium persulphate, as assistant radical initiator for gamma crosslinking. Selected hydrogels weretested through swelling measurements to prove their pH and electric field responsiveness. Structural featuresof the different variants produced were related to the swelling behaviour.