ISO DIS 16014-2

Description / Abstract: This document specifies a method for determining the average molecular weight and the molecular weight distribution of polymers using size-exclusion chromatography (SEC). The average molecular weight and the molecular weight distribution are calculated using a universal calibration curve instead of the conventional calibration curve.

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NOTE The concept of the universal calibration method is based on a relationship by which the retention time in SEC depends on the size of the polymer molecule (the hydrodynamic volume) or on the product of the intrinsic viscosity [η] and the molecular weight M. Many polymers classified as random-coil polymers (regardless of their chemical structure, degree of branching, composition or tacticity) have been experimentally confirmed as following this relationship. The universal calibration curve is prepared by plotting the logarithm of [η]M against the elution time t or elution volume V using polymer standards such as polystyrene with narrow molecular weight distributions. The molecular weight Mi of an unknown polymer sample can then be calculated from the value of [η]M at each retention time using the universal calibration curve and [η] or K and a in the Mark- Houwink-Sakurada equation ([η] = KMa → [η]M = KM^a+1), where K is a constant and a is an exponent depending on the experimental conditions. Therefore this test method is classified as a relative method as described in ISO 16014-1, but the average molecular weights and molecular weight distributions calculated by the method are equal to, or nearly equal to, the absolute values.