Organic/inorganic Dual Network Hydrogels Based on Acrylic Acid and 2-aminoethyl-3-aminopropyltrimetoxysilane: Synthesis and Characterization

A novel dual network (DN) hydrogel composites based on partially neutralized polyacrylic acid (PAANa) and poly-N-(2-aminoethy1)-3-aminopropy1trimethoxysi1ane (PAPTMS) were synthesized by a combination of free radical polymerization of AANa in the presence of N,N'-methylenebis(acrylamide) cross-linker and hydrolysis of silica precursors and catalytically-induced condensation of the resulting hydroxyl groups of APTMS (from 5 to 20 wt.%) to form a network structure. The cross-linking of PAANa was verified by the absence of a C=C double bond by FTIR analysis. TGA of PAANa/PAPTMS hydrogels showed higher thermal stability compared to pure PAA hydrogel as well as the heat-resistance index (TiiRi) for PAANa/PAPTMS composites have greater values than additive ones. The hydrogels' swelling capacity in distilled water is enhanced by 316% (from 16.81 to 70.06 g/g) at the incorporation of 10 wt% of PAPTMS. The mechanism of diffusion of hydrogels (except PAANa/PAPTMS = 80/20) has non-Fickian or anomalous character. The sorption curve of PAANa/PAPTMS = 80/20 sample has sigmoid character and was interpreted as a result of a combination of first-order kinetics and the overall autocatalytic process with its two rate constants.