Gel permeation chromatography GPC , also known as size exclusion chromatography SEC , is a widely used technique to determine the molecular weight of polymers. The molecular weight of a polymer is a critical parameter that influences its properties and behavior, such as mechanical strength, viscosity, solubility, and thermal stability. Understanding the molecular weight distribution of a polymer can help in optimizing its processing conditions and tailoring its properties for specific applications.In GPC, a polymer sample is dissolved in a suitable solvent and then passed through a column packed with porous gel particles. The gel particles have a range of pore sizes that can accommodate polymer chains of different sizes. As the polymer solution flows through the column, the polymer chains are separated based on their size hydrodynamic volume . Larger polymer chains cannot enter the pores and elute faster, while smaller chains can enter the pores and take longer to elute.To determine the molecular weight of a polymer using GPC, the following steps are typically followed:1. Calibration: A set of polymer standards with known molecular weights and narrow molecular weight distributions are analyzed using the GPC system. The elution volume or retention time of each standard is recorded, and a calibration curve is constructed by plotting the logarithm of the molecular weight versus the elution volume or retention time .2. Sample analysis: The polymer sample of interest is analyzed using the same GPC system and conditions as the calibration standards. The elution volume or retention time of the sample is recorded.3. Molecular weight determination: The elution volume or retention time of the sample is compared to the calibration curve to determine the molecular weight of the polymer. The molecular weight distribution can also be obtained by analyzing the full chromatogram of the sample.It is important to note that GPC provides relative molecular weight values, as the separation is based on the hydrodynamic volume of the polymer chains, which can be influenced by factors such as the polymer's conformation and the solvent used. Nevertheless, GPC remains a valuable tool for characterizing the molecular weight and molecular weight distribution of polymers, providing essential information for understanding their properties and behavior.