Viscosity of polyisoprene

The effects were studied of molecular weight, shear rate, and temperature on the viscous behavior of various linear, monodisperse polyisoprenes of about 90% cis ‐1,4 structure. Viscosities of from 10 10 ‐10 5 poise were measured on a double cone and plate viscometer while viscosities of 10 4 ‐10 −2 poise were measured on rotating cylinder viscometers. For such polyisoprenes the variation of Newtonian (zero shear) viscosity η with the weight‐average molecular weight in the molecular weight range of 2 × 10 4 ‐1 × 10 6 may be represented as\documentclass{article}\pagestyle{empty}\begin{document}$\eta = A\bar M_w^{3.9_5}$\end{document} where A is a temperature‐dependent parameter given by\documentclass{article}\pagestyle{empty}\begin{document}$\log A = - 101.14 + \frac{{8.999 \times 10^4}}{T} - \frac{{3.19222 \times 10^7}}{{T^2}} + \frac{{3.816 \times 10^9}}{{T^3}}$\end{document} The variation of the apparent viscosity η a with shear rate is also determined and a combined equation may be formulated as\documentclass{article}\pagestyle{empty}\begin{document}$\eta _{\rm a} = A\bar M_w^{3.9_5} /[1 + 1.22(A\dot \gamma /T)^{0.58} \bar M_w^{2.87} \times 10^{- 5}]$\end{document} This equation is compared with other expressions for the variation of viscosity with molecular weight, temperature, and shear rate.