Material properties imaging of cross-linked polymers by NMR

Spatially resolved investigations of molecular properties in polymer materials are shown to be possible by means of parameter-selective NMR imaging. The transformation of NMR parameters into material properties can be performed using a suitable theoretical description of the molecular mobility in the polymer under investigation. Rubber samples consisting of three pieces of rubber with different crosslink densities have been investigated in a first experiment. A series of images which were progressively weighted by transverse relaxation have been acquired by application of a spin-echo back-projection technique. The relaxation was analyzed pixel by pixel using a single chain model for the molecular dynamics of the polymer network. Parameters directly related to material parameters, such as cross-link density and correlation times, could be derived from the theory and were displayed in the form of a Material Property image (MAP image). In contrast to conventional spin density images, wher e the different pieces of rubber could not be distinguished properly, the MAP image clearly reflects the different cross-link densities. Moreover, histogram analysis of the image can be used for the characterization of cross-link density inhomogeneities.