Raman spectroscopic characterization of association and thermoreversible gelation in aqueous systems of poly(N-acetamidoacrylamide)

Polymer self-association and thermoreversible gelation in aqueous solutions of poly(N-acetamidoacrylamide) (PAAA) have been investigated by Raman spec troscopy. We found that aqueous solutions of PAAA, even at low concentratio ns, revealed the presence of polymer-polymer coordination, suggesting forma tion of polymer clusters. The effect of denaturant (sodium thiocyanate) on the inter- and intramolecular interactions in the system has been also stud ied. It is shown that the SCN ions destroy the macroscopic hydrogen-bond ne twork of water, as well as reduce the polymer's ability for self-associatio n by occupying the NH groups. The changes observed in the Raman spectra upo n the gel transition show that in the gel state the equilibrium of the syst em is shifted toward polymer-polymer coordination, whereas in the solution it is mostly polymer-water coordination. The influence of the different fac tors such as polymer concentration, level of denaturant addition, and type of solvent on the gel formation is discussed.