Imidization reaction in polyvinylamides

Abstract

AbstractDepending on their method of preparation, polyvinylamides can have nitrogen contents which vary from the theoretical value to considerably lower values. Cyanamer P‐250, a polyacrylamide, manufactured by American Cyanamid Corporation, had a nitrogen content of 17.67% compared to the theoretical value of 19.7%. A polyacrylamide prepared in dioxane at 60°C and initiated by benzoyl peroxide, had a nitrogen content of only 15.5%. These low values are ascribed to loss of ammonia via intramolecular imide formation. We have found that when the intramolecular imidization reaction in poly acrylamide and in polymethacrylamide is driven to completion by heating the polymers in dilute solution, very close to 33% of the amide groups remain unreacted. Thus, unlike poly(methyl vinyl ketone) and poly(vinyl chloride), the poly‐vinylamides do not obey Flory's statistical calculation for the random reaction of 1,3 groups in a head‐to‐tail polymer which predicts isolation of only 13.53% of the vinyl residues. Of the various possible explanations, the hypothesis of larger ring formation seems the most plausible, since specific interactions have been shown to exist between widely spaced amide groups in low molecular weight diamides. The infrared spectra of polyacrylimide and polymethacrylimide are presented and compared with those of the corresponding polyvinylamides. When the nitrogen content of polyacrylamide falls to the 14.9–15.4% N range due to imide formation, the polymer becomes water‐insoluble. Because imidization stiffens the polymer chain and introduces weakly acidic groups, the imide content of a polyvinylamide should affect its compatibility with other polymeric systems.