A colourimetric method for the determination of the degree of chemical cross-linking in aspartic acid-based polymer gels

A 2,4,6-trinitrobenzenesulphonic acid (TNBS)-based assay is developed to determine the degree of chemical cross-linking in aspartic acid-based polymer gels. The conventional colourimetric method for the quantitative determination of amine groups is difficult to use in polymer networks; thus, an improved method is developed to analyse polymer gels swollen in dimethyl sulfoxide (DMSO). Reaction products of the derivatizing reaction are examined by NMR. The chemical stability of the reagent is increased in DMSO, and the method shows satisfactory linearity and accuracy. The degree of chemical cross-linking in the investigated gels is close to its theoretical maximum, but the conversion of the pendant amine groups to cross-linking points is strongly dependent on the feed composition of the gels.