High molecular weight hydrolyzed polyacrylamides. III. Effect of temperature on chemical stability

The effect of temperature (100°C) and heating time (up to 384 hr) on the physicochemical properties of high molecular weight (M̄p ≅ 4 × 106) partly hydrolyzed (τ ≅ 31%) polyacrylamide (HPAM-25) solutions with initial pH values near 4 and 7, respectively, is reported. Potentiometric and spectroscopy data indicate that upon heating the solutions for 16 days the extent of hydrolysis is increased up to around 90%. The viscosity behavior, especially in the presence of bivalent salt (CaCl2), can be explained by taking such an increase in hydrolysis into consideration. From light scattering data, it is shown that the conformational changes are not correlated with molecular weight degradation.