Transient entanglement behaviour in a poly(propylene glycole) melt: A field gradient NMR self-diffusion study

We report measurements of the temperature dependence of the self-diffusion of a poly(propylene glycole) in the melt. Two kinds of magnetic field gradient NMR are used: pulsed field gradient NMR with large field gradients and static field gradient NMR in a specially designed cryomagnet. The emphasis is put on large field gradients. The (true) longtime self-diffusion coefficients are compared with those calculated from normal-mode relaxation times in dielectric spectroscopy using the Rouse model. They agree very well. For temperature below about 270 K, a time-dependent self-diffusion coefficient appears which is an indication of anomalous diffusion. At 253 K we observe complete transient entanglement behaviour of the PPG melt. These results are discussed in comparison with dielectric and other experimental data.