DIFFUSION OF OLIGOMERIC SPECIES IN POLYMER-SOLUTIONS

Self-diffusion coefficients (D(s)) for analogs of polystyrene (PS) oligomers were measured using pulsed field gradient (PFG) H-1 NMR as a function of the weight fraction (w(p)) of high molecular weight PS (125000-250000) in solution over the range 0 less-than-or-equal-to w(p) less-than-or-equal-to 0.6. The studies were performed at 25-degrees-C using benzene as solvent. Model compounds used were benzene, 1,3-diphenyl-1-butanol, and a commercially-available, monodisperse sample of PS (so-called M5) of a peak-average molecular weight of M(p) = 580 as determined by gel permeation chromatography (GPC). GPC data and PFG NMR data were used to determine a new average molecular weight for M5 of 500. The scaling law dependence of the D(s) values on the molecular weight of the model compounds was determined and a simple scaling dependence was observed with the scaling law changing linearly with w(p) over the range studied. This is discussed in light of current models. D(s) data are also presented for the diffusion of toluene in toluene/PS solutions over the range 0 less-than-or-equal-to w(p) less-than-or-equal-to 0.7 and are 20%-30% smaller than identical experiments reported by Pickup and Blum (see ref 13).