Measurement of Crosslinking Density of Rubbers by Analyzing Gaussian-Weighted 1H CPMG Relaxation Curves

CPMG sequence is widely used to measure crosslink density of rubber. However, the crosslink density obtained by this technique has a strong dependence on the interval times between the pulses in CPMG sequence, and the results measured have only a weak correlation with rubber hardness. To overcome this shortcoming, we proposed in this work to construct a 1H T2 relaxation curve by summing Gaussian-weighted CPMG relaxation curves acquired at by varying the interval time between the pulses in CPMG sequence. Using the multi-echo Gaussian-weighted relaxation curve to calculate the crosslink density gave results that had greatly improved correlation with the rubber hardness. The new method was also fast and efficient, as it took only one-tenth of the experimental time required for the conventional 1H double quantum NMR (1H DQ NMR) experiment.