Polymers and group interaction. IV. Hofmann reaction on polyvinylamides

Abstract

AbstractThe Hofmann degradation reaction has been applied to polyvinylamides in order to obtain aminocarboxylic polyampholytes. When the reaction is effected in aqueous solution, interactions occur between isocyanate and neighboring chloroimide ions, with the formation of butyrolactam ring units incorporated in the polymeric chain. The structural composition of the polymers has been determined on the basis of the following analytical results: total and volatile nitrogen, total and ionic chlorine, and conductometric and potentiometric titrations. In the case of polymethacrylamide the end product consists of about 57% lactam rings, 28% free amine chlorohydrate, and 8% methacrylic acid units, while about 5 to 6% amide groups remain unreacted. In the case of polyacrylamide the degree of conversion is usually lower; this difference in behavior has been interpreted as being due to the high substitution in the methacrylic derivative. When the reaction is effected in water‐methanol (50/50) solution, any ring formation is absent; contrariwise, the isocyanate functions are transformed into carbamate units. In alcoholic medium it is possible to obtain polymers containing about 50% carbamic functions, as well as small amounts of free amines (3%); the residual percentages are acid or unreacted amide groups. On alkaline hydrolysis of these carbamic functions, free amine functions are produced; however, the rate of hydrolysis is very low if compared to that of usual amides. This effect has been attributed to the nitrogen substitution in the carbamate units magnified image and to the electrostatic repulsion effect of the carboxylate functions toward the hydroxyl ion. For verification, the alkaline hydrolysis rate constants of N‐isopropyl methylcarbamate have been compared with those of methylcarbamate; they were found to be about ten times slower. Moreover, the corresponding activation energy of alkaline hydrolysis was 18.7 kcal./mole instead of 14.1 in the case of the unsubstituted methylcarbamate. The products obtained by Hofmann degradation on polymethacrylamide have been compared to those obtained by Lossen rearrangement reaction on polymethacroyl chloride; the structural units were found to be identical in both cases.