New superabsorbent hydrogels synthesized by copolymerization of acrylamide and N-2-hydroxyethyl acrylamide with itaconic acid or itaconates containing ethylene oxide units in the side chain

A series of acrylamide/itaconic acid (AAm/IA), acrylamide/monomethoxyethyl itaconate (AAm/MEI), and acrylamide/dimethoxyethyl itaconate (AAm/DEI) hydrogels were synthesized in AAm/comonomer molar ratios of 100/0, 90/10, 80/20, and 70/30. In all cases, almost quantitative yields were obtained, and the swelling ability increased when comonomer proportion increased. AAm/MEI and AAm/IA reach swelling values more than 40,000, and both systems swelled more than AAm/DEI. This fact pointed out that the carboxylic acid groups present in IA and MEI are mainly responsible for the swelling. All of these hydrogels are stable up to 150 degrees C as indicated by the TGA measurements. For comparison, the synthesis of a series of N-2-hydroxyethyl acrylamide/itaconic acid (HEAAm/IA), N-2-hydroxyethyl acrylamide /monomethoxyethyl itaconate (HEAAm/MEI), and N-2-hydroxyethyl acrylamide /dimethoxyethyl itaconate (HEAAm/DEI) hydrogels were also carried out. The swelling behavior of HEAAm/IA and HEAAm/MEI was opposite to the former; in these cases the presence of the itaconate comonomer diminish the swelling ability. A diffusion mechanism study was carried out for all the series.