NATURE OF THE PROTON NMR TRANSVERSE RELAXATION FUNCTION OF POLYETHYLENE MELTS .1. MONODISPERSED POLYETHYLENES

Results are presented for NMR measurements on a series of samples of linear polyethylene with low polydispersity over a range of molecular weights. In general terms, the experimental data are consistent with results of previous workers. The main thrust of the present investigation is to show that the transverse relaxation function can be accurately described by a recent theoretical model due to Brereton. This theory is based on a scale-invariant model of the dipolar interactions assumed responsible for the relaxation of transverse magnetization. It incorporates a rather general hierarchy of chain dynamics which can be used to accommodate the Rouse model at small space and time scales and a variety of other models, e.g., the reptation model, at larger space and time scales. The model is shown to account for the complex shape of the transverse relaxation function observed for high molecular weight samples of low polydispersity, showing that this has its origin in the restrictions on molecular mobility imposed by the entangled nature of the polymer melt.