Network defects in polyacrylamide gels

Abstract

The weight conversion at the gel point ( α G w) was determined by the gas bubble method in two sets of polyacrylamide (PAA) gels crosslinked with N, N′-methylene-bisacrylamide (BA). α G w remained practically constant when the crosslinker ratio was C = 10% (w/w) and the total concentration of comonomers in the feed ranged from C T = 5 to 10 g/100 ml. When C T was kept constant at 5 g/100 ml and C changed from 0 to 25% (w/w), α G w showed a minimum at C = 7%. By comparing the experimental values of α G w with those calculated for an ideal network, it was concluded that the crosslinking efficiency of BA is very low. The dependence on C of α G w and other properties like the elastic phantom modulus, | ƒ ph ∗ |, and the polymer volume fraction at swelling equilibrium, v 2s o , was explained in terms of the formation of network defects: the formation of BA sequences longer than unity and that of intramolecular cycles both have an increasing contribution at C > 7% but can be neglected at lower values of C.