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1H NMR Study of Hindered Internal Rotation and Hydrogen Exchange of Amide Side Chain of Poly(acrylamide) in Aqueous Solution

Structure and dynamics properties of poly(acrylamide)(PAAm) side-chains are investigated by 1H NMR methods. The multiplicity of 1H spectra of NH2 protons of PAAm side-chains is attributed to the tacticity splitting at the triad level. The proton exchange and the hindered internal rotation of the NH2 group are studied by examining pH and temperature dependences of the 1H spectra. It is found that the proton exchange rates of the two NH2 protons with solvent water are almost the same. The activation energy of hindered internal rotation is found to be about 58±9 kJ mol−1. The present results indicate that there is no hydrogen bonding between amide groups of neighboring units.