Characterization of Low-Molecular-Weight Polymers: Failure of Universal Calibration in Size Exclusion Chromatography

Abstract Accurate measurement of molecular weights for polymers in the 500–5000 molecular weight range requires considerable care. Absolute methods such as membrane osmometry or light scattering are generally imprecise because of membrane permeation or low scattering intensity. Many polymers are too fragile to be studied by mass spectrometry. Other techniques, such as vapor phase osmometry, cryoscopy, and ebulliometry require calibration and data replication if accurate molecular weights are to be obtained. Size exclusion chromatography (SEC) also requires calibration but can be a very rapid and accurate method if proper calibration can be achieved. SEC calibration is now often achieved via “universal calibration” (UC). which is based on the premise that polymers with the same hydrodynamic volume will have the same SEC retention time, At very low molecular weights, the UC approach is clearly invalid since intrinsic viscosities can become negative for certain polymers. We demonstrate here that the invalidi...