AbstractMeasurements of the viscosities of a number of polymer‐solvent systems have shown that an exponential expression, η = η0eηc, is applicable in the Concentration range up to c = 0.13 g./lOO cc. of solvent to within the precision of the experimental measurements. This exponential equat.ion lends itself readily to the determination of the intrinsic viscosity ηfrom a single determination of η/η0 and is therefore of great use in determining molecular weights of high polymers from a Houwink‐type expression. At higher concentrations, departures from the exponential equation occur, but agreement remains reasonably good up to a con‐ centration of 1 g./l00 cc. of solvent. The experimental results are compared with those predicted by the exponential expression and with those expected from a Huggins‐type equation in which k′ = 0.5, which corresponds to the first two terms of the expanded form of
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