Calculations of diffusion coefficients of cyclic poly(dimethylsiloxanes)

Abstract

The Kirkwood equation and a Monte‐Carlo technique which employs Metropolis sampling have been used to calculate diffusion coefficients (D) for low molar mass cyclic poly(dimethylsiloxanes). Correlations between calculated and experimental values of D show that the effective segment size is larger for cyclic than for linear PDMS. Thus, free‐draining flow is reduced for the cyclic species consistent with its greater segment density. The cyclic molecules also show enhanced diffusion coefficients at very low molar masses which may be associated with the rigid toroidal shapes of these molecules.