Self-Diffusion in Linear Dimethylsiloxanes

Abstract

The pressure and temperature dependences of the self-diffusion coefficients of the linear dimethylsiloxanes, containing from two to nine silicon atoms have been determined by the NMR spin-echo technique. Activation energies and volumes are presented as derived quantities; the constant-volume activation energy is estimated from these data. Extensive comparisons between the diffusion properties of the dimethylsiloxanes and equivalent hydrocarbons are made. From these comparisons, it is concluded that diffusion in siloxanes is controlled to a much larger extent by chain configurational effects. This concept is formalized by expressing the chain-size effects in an entropy of activation model.