Hydrolysis of polyacrylamide and acrylic acid–acrylamide copolymers

Abstract

AbstractThe hydrolysis of polyamides has been studied in buffered acid solution at 110°C. at an amide concentration of 0.05 M. In the case of polyacrylamide, the reaction was carried out in acetate buffer at different values of the ratio r (acetic acid/sodium acetate). The initial velocity is low and is proportional to the concentration of acetic acid; the rate constant is equal to 2.6 × 10−6; this reaction accelerates, however, as soon as the degree of conversion exceeds 3 to 5%. In the case of copolymers of acrylamide and acrylic acid (r1 = 1.38 and r2 = 0.36, respectively), the reaction proceeds in two distinct steps, of which the first is about 50 to 100 times more rapid than the second. By carrying out the reaction with copolymers of different composition (70, 74.5, 85, and 88 mole‐% acid) and varying the degree of neutralization for each (r = 2, 10, and 49), it is shown that the rapid first step results from the interaction between an amide group and an undissociated, directly neighboring acid group, which moreover must be present in a welldetermined stereochemical position. The stereospecificity of the kinetics of this reaction was demonstrated by the difference in the behavior of two copolymers of the same over‐all composition but different internal structure. The slow second step of the hydrolysis of the copolymer corresponds sensibly to the action on polyacrylamide by external acid; the retardation is a consequence of the fact that the requirements of vicinality and stereospecificity are not satisfied for the residual for the amide groups.