THE EFFECT OF FIELD INHOMOGENEITIES AND MOLECULAR-DIFFUSION ON THE NMR TRANSVERSE RELAXATION BEHAVIOR OF POLYMER MELTS

The formation of spin-echoes in the Carr-Purcell-Meiboom-Gill (CPMG) NMR experiment on rubbery polybutadiene (PBD) has been studied as a function of temperature and CPMG inter-pulse spacing. The influence of internal field gradients, and of diffusional motion of the polymer segments during the inter-pulse periods is demonstrated. The CPMG decays are well described by diffusion equations for the case of diffusion of particles through connecting cylinders. Microscopic voids of diameter of similar to 0.5 nm adjacent to the reptating chain segments are suggested to be responsible for the magnetic field gradients