OBSERVATION OF CROSS-LINK DENSITY DISPERSION IN SULFUR-DONOR VULCANIZED POLYBUTADIENE USING NMR IMAGING

Proton NMR imaging techniques have been applied to the investigation of two-dimensional structure in TMTD-vulcanized cis-polybutadiene. Unfilled PB samples of different cross-link densities were swollen with deuterated solvent and directly imaged, using single and multiple spin-echo NMR imaging (NMRI) pulse sequences. The resulting T2-weighted and T2-resolved images display a variety of structural detail. Major structural voids, compression- and reaction-induced gradients of chain segment mobility, and general spatial inhomogeneity in the cross-link density of these samples have been observed. A simple analytical model has been applied to interpret changes in the distribution of T2 values with increasing cure time. The results of this work form the basis for quantitative assessment of spatial variations in the cross-link density of PB from T2-resolved images of the material.