Meaning
Liquid chromatography systems operating at elevated temperatures allow for the molecular weight characterisation of semi-crystalline polymers like polyethylene and polypropylene. High temperature GPC is required because these resins are insoluble in common solvents at room temperature. The technique uses heated columns and detectors to keep the polymer in solution while it is separated based on hydrodynamic volume.
Solvent System
Chemical compatibility at high heat is a requirement for the mobile phase used in this analysis. High temperature GPC typically employs chlorinated solvents like trichlorobenzene at temperatures between 140 and 160 degrees Celsius. These conditions require specialized seals and pumps that can withstand the corrosive nature of the solvent and the thermal expansion of the system components.
Resolution Factor
Separation efficiency depends on the choice of column packing and the flow rate of the heated solvent. In high temperature GPC, the pore size of the stationary phase must be matched to the expected molecular weight range of the polyolefin. This ensures that the largest chains are excluded from the pores while the smaller chains are delayed, creating a clear distribution curve.
Calibration Curve
Standards of known molecular weight provide the reference points needed to convert elution time into a mass measurement. Because high temperature GPC is a relative method, the use of narrow distribution polystyrene standards is common, followed by a mathematical correction for the specific polymer being tested. This process enables a moulder to compare different resin lots and predict how they will behave in a high shear injection moulding environment where molecular weight dictates the final part strength.
Accurate molecular data is the primary way to avoid batch-to-batch variation in structural automotive parts.
