Diffusion of Polymer Rings in Linear Polymer Matrices

Abstract

Forward recoil spectrometry has been used to determine concentration profiles and tracer diffusion coefficients D* of undeuteriated polystyrene rings of molecular weight M, ranging from 10 000 to 180 000, diffusing into deuteriated linear polystyrenes (PS) of molecular weight P, ranging from 55 000 to 915 000. Although constraint release has been proposed as the dominant diffusion mechanism for the rings, giving D* ∽ M-1P-3, this scaling is only observed at low P's. For the highest P's we find D* ∽ M-3.2P-n, where n increases from approximately 0 at M = 10 000 to 1.6 at M = 180 000. In magnitude the data fall above the constraint release prediction and below the measured D*,s for linear PS of the same M. These results indicate two additional diffusion processes for rings: (1) the restricted reptation of that fraction of rings that is unthreaded by linear P-chain constraints, a process recently proposed theoretically by Klein; (2) constrained ring diffusion, in which that fraction of rings threaded once by P-chain constraints diffuses along these linear constraints. Predictions based on these processes are in satisfactory agreement with the experimental data. © 1987, American Chemical Society. All rights reserved.