The hindered internal rotation of amide groups of polyacrylamide of low molecular weights.

Polyacrylamides of low molecular weights (average degrees of polymerization(‾DP) : 7.2, 18.3, 21.3, and 45.4) were prepared by radical polymerization, and their PMR spectra were observed over the temperature range of 30–90 °C. From the temperature dependence of the PMR spectra, the values of the energy barrier to the internal rotation about C–N bonds were determined by means of a total line-shape analysis. The energy barriers for the polymers above ‾DP : 18.3 were 10.6 kcal/mol, while those for the polymer of ‾DP : 7.2 were 9.2 kcal/mol. These results were interpreted in terms of the local environment around the amide groups. The intramolecular hydrogen bonding was also investigated.