Polymer Rheology
An IV drop of 0.16 dL/g is not a small number: it is four chains broken for every ten that entered the dryer.
— dL/g
Billmeyer single-point, from one efflux pair
The Billmeyer equation is a truncation and is at its best between about 0.4 and 1.2 dL/g at 0.50 g/dL; outside that window run a dilution series. Efflux times must come from the same viscometer at the same bath temperature, because the ratio only cancels the geometry if the geometry is identical - a different tube constant invalidates the pair even if both times look reasonable. Solution concentration should be corrected for chip moisture if the sample was not dried, since an undried chip weighs more than the polymer it contains and reports a low IV. The chain scission figure assumes random scission of a most-probable distribution and counts only main-chain breaks; it does not distinguish hydrolytic from thermal cause, and it says nothing about branching or gel, which raise viscosity while degrading the polymer.
Polymer Intrinsic Viscosity, Molecular Weight & IV Drop Calculator — free, with the formula and a worked example, at Textile School.