Viscosity of polydimethylsiloxane–pentamer systems

Viscosities of polydimethylsiloxane–pentamer systems were measured over the whole range of concentration. Twelve samples having molecular weights from about 1000 to 5 × 10 5 were studied. The empirical reduction scheme, plots of log η versus log c M 0.68 , suggested by Ferry and co‐workers is applicable to samples of M̄ v ≥ 22,000 over the entire concentration. Such satisfying superposition of data may be attributed to the systems being the homologous mixtures in which glass temperatures of polymers are very low. On the basis of the treatment of Fox and Allen, the effects of the number and weight‐average molecular weight on viscosity were examined, and the friction coefficient ζ per chain atom at constant M̄ n was calculated over a wide range of M̄ n . The value ζ is almost constant (ζ = 7.4 × 10 −9 dyne‐sec./cm.) in the region of M̄ n ≥ M c , and where otherwise it decreases rapidly with decreasing M̄ n . The length of the chainend segment was tentatively calculated.