Synthesis and characterisation of chemically crosslinked N-vinyl pyrrolidinone (NVP) based hydrogels

Crosslinked complexes of polyvinyl pyrrolidinone-polyacrylic acid (PVP-PAA) were prepared from a mixture of NVP, AA and ethyleneglycol dimethacrylates. The FTIR spectra of PVP-PAA copolymer complexes indicates both hydrogen bonded and non-hydrogen bonded PVP. Swelling of the PVP-PAA complex in a higher pH medium is significantly different from results in low pH solutions. Above the critical pH of the copolymer the carboxylic acid group of AA ionize. Therefore there is a reduction in the intermolecular bonding and so the hydrogels tend to swell to a greater degree yielding higher 'water content' and 'water uptake' values. The rheometry results indicated that there was a significant difference in the comparative gel strength at different pHs due to the increased water uptake. It was also found that by varying the molecular weight of the crosslinking agent an increase in comparative gel strength could be achieved.