Semi-IPNs based on polyacrylamide (PAAm) and poly(itaconic acid) (PIA) were prepared by two different techniques, polymerizing itaconic acid in the presence of polyacrylamide gel (Samples I) and by makiug the polyacrylamide gel in the presence of poly(itaconic acid) (Samples 11), with different PAAm/PIA ratios. The swelling behavior of the semi-IPNs reveals that gels with low PIA content swell more, while those with high PIA content swell less than a pure PAAm gel, probably due to the formation of intermacromolecular gel-polymer complexes on the basis of hydrogen bonds. The results of thermal analysis indicate an improved therinal stability of the hydrogels and complexes compared with PIA and PAAm.