Effect of varying crosslinking density on polyacrylamide gels

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Abstract
The copolymerization of acrylamide and N, N′-methylene bisacrylamide has been investigated over a wide range of total monomer concentration (T) and with the proportion of the crosslinking monomer (C) varying from 0 to 100%. The threshold value of the total monomer concentration above which gel formation becomes possible decreases as C increases. Gels with high C (>4%) become turbid and eventually opaque. An analogous phase separation is observed in the sol phase, where actual precipitation of a branched polymer takes place. The gelation curve continues into the phase separated region. Raman spectroscopy of gels with different values of C indicates that the opacity is related to the formation of cluster of varying sizes, with varying amounts of the monomers. The spectral data also shows that the BIS molecules may aggregate and that some unreacted vinyl groups of the BIS molecules are incorporated into the polymer network.

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