Synthesis and Characterization of Polyacrylamide Hydrogels

Polymer hydrogels are cross-linked hydrophilic polymers which are insoluble but absorb, swell and retain large amount of water. They exhibit both liquid and solid like properties. Such polymers have wide range applications in biotechnology, biomedical, pharmaceutical, agriculture, water treatment and many other areas. We carried out a free radical polymerization of acrylamide in an aqueous solution of HNO3 where no other initiator was present. A highly crossed linked polymer gel was obtained. The dried gels were brittle and glassy in appearance. They swell in water and equilibrium swelling is obtained after several days. The water intake of the gels substantially increased when the polymer was subjected to an alkaline saponification. The water absorbency of hydrolysed polymer was found to be more than 1000 times their own mass. The polymer chains contain both an amide and a carboxylate groups. The water molecules in the solvent are attracted by dipole-dipole attraction and hydrogen bonding through nitrogen-oxygen and oxygen-oxygen bonding thereby giving a high degree of swelling. The unhydrolysed polyacrylamide is neutral and has a randomly coiled configuration having consequently low swelling. On the other hand the hydrolysed polymer has ionic character with an extended chain configuration. Such polymers display a better swelling behaviour. The degree of swelling of prepared polyacrylamide hydrogels depend on water pH. In neutral medium swelling is also reversible because the same sample of hydrogels undergoes several cycles of swellings and deswellings