Polymer Intrinsic Viscosity, Molecular Weight & IV Drop Calculator

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 7 inputs are read from the form on every keystroke: Solution Efflux Time, Solvent Efflux Time, Solution Concentration, Mark-Houwink K, Mark-Houwink exponent a, Repeat Unit Molar Mass and Incoming Chip IV.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Intrinsic Viscosity together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Number-Average Molecular Weight, Degree of Polymerisation, IV Drop from Chip, IV Drop, Chain Scissions per Original Molecule, Relative Viscosity, Specific Viscosity and Reduced Viscosity — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

Substituting

Four chains broken for every ten that went in. A 20% IV drop is a dryer problem, not a spinning problem - PET hydrolyses in the melt at a rate set by the moisture it carried into the extruder, and no screw profile recovers it.

How to use it

1. Work through the input groups in order — Viscometry and Polymer Constants. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read Intrinsic Viscosity in the dark results panel — that is the headline figure, expressed in dL/g.
4. Check the supporting rows underneath (Number-Average Molecular Weight, Degree of Polymerisation, IV Drop from Chip, IV Drop, Chain Scissions per Original Molecule, Relative Viscosity, Specific Viscosity and Reduced Viscosity) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing Intrinsic Viscosity before a trial is booked, so machine time and material in Polymer Rheology & Synthetic Extrusion are committed against a calculated figure rather than an estimate.
• Costing and quotation — Intrinsic Viscosity is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Solution Efflux Time) shows how much of the gap in Intrinsic Viscosity each variable explains.
• Teaching and study — the accepted ranges bracket normal Polymer Rheology & Synthetic Extrusion practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Reading the result

Typical bands and what each one is telling you.

Assumptions and limits

• 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.
• Every input is bounded to the range normal practice occupies (Solution Efflux Time 10 to 3000 s, Solvent Efflux Time 10 to 3000 s and Solution Concentration 0.05 to 2 g/dL, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Standards and further reading

• ASTM D4603 - Standard Test Method for Determining Inherent Viscosity of PET by Glass Capillary Viscometer, which specifies 60/40 phenol/1,1,2,2-tetrachloroethane at 30 C and 0.50 g/dL.
• ISO 1628-5 - Determination of the viscosity number and limiting viscosity number of thermoplastic polyester homopolymers and copolymers.
• ASTM D2857 - Standard Practice for Dilute Solution Viscosity of Polymers, the dilution-series reference this single-point method approximates.
• Billmeyer, F. W. (1949), Journal of Polymer Science 4, 83 - the origin of the single-point equation used here.

Questions people ask