Preparation and characterization of hydrogels based on homopolymeric fractions of sodium alginate and PNIPAAm.

Graft copolymers were prepared by formation of an amide bond between poly-α-L-guluronic acid (MW 24,000), isolated from sodium alginate and the free amino group of PNIPAAm-NH(2). SEM micrographs revealed the formation of a macroscopic network on the surface of the grafted hydrogels with a porosity diameter of 10-20 μm. Semi-IPN hydrogels were prepared using different proportions of sodium poly-β-D-mannuronate (MW 21,000), isolated from sodium alginate and cross-linked PNIPAAm-NH(2) polymers. SEM micrographs showed porosities of minor size (∼5 μm). Though both types of hydrogels are good water containers, the water retention capacity of graft copolymers is more than 50% higher than that of semi-IPN hydrogels. Both hydrogel types showed significant changes in swelling ratios between 20 and 45 °C: the swelling ratio decreases near the LCST of PNIPAAm. The water absorption and retention capacity of graft hydrogels increases with pH, reaching a maximum value at pH 7.0.