Comparison of Three NMR Methods for Measuring Crosslink Density of Rubbers

NMR is a frequently used technique for measuring crosslink density of rubbers. In this work, three commonly used proton NMR methods for measuring crosslink density of rubbers[i.e., 1H double-quantum (DQ) NMR, 1H Hahn echo and 1H CPMG echo] were compared. Different approaches showed different results, and the origin of such discrepancy was discussed. The echo time dependence of the crosslink density measured with the CPMG echo method was studied. The ways to improve theCPMG echo-based measurements are discussed.