Mark–Houwink equation

:[1][2] From this equation the molecular weight of a polymer can be determined from data on the intrinsic viscosity and vice versa.

For polymers with an absolute rigid rod, such as Tobacco mosaic virus,

It is named after Herman F. Mark and Roelof Houwink.

The Mark-Houwink equation is used in size-exclusion chromatography (SEC) to construct the so called universal calibration curve which can be used to determine the molecular weight of a polymer A using a calibration done with polymer B.

In SEC molecules are separated based on hydrodynamic volume, i.e. the size of the coil a given polymer forms in solution.

This means that the molecular weight associated with a given retention volume is substance specific and that in order to determine the molecular weight of a given polymer a molecular-weight size marker of the same substance must be available.

However, the product of the intrinsic viscosity and the molecular weight,

, is proportional to the hydrodynamic radius and therefore independent of substance.

For example, if narrow molar mass distribution standards are available for polystyrene, these can be used to construct a calibration curve (typically

This calibration can then be used to determine the "polystyrene equivalent" molecular weight of a polyethylene sample if the Mark-Houwink parameters for both substances are known in this solvent at this temperature.