Size-exclusion chromatography SEC , also known as gel permeation chromatography GPC or gel filtration chromatography, is a widely used technique for determining the molecular weight distribution of polymers. The method separates polymer chains based on their hydrodynamic volume or size in solution rather than their chemical properties. Here's a step-by-step guide on how to use SEC for determining the molecular weight distribution of polymers:1. Preparation of the sample: Dissolve the polymer sample in a suitable solvent to create a homogeneous solution. The concentration should be low enough to avoid intermolecular interactions, typically around 1-5 mg/mL.2. Selection of the column and stationary phase: Choose an appropriate SEC column and stationary phase gel based on the molecular weight range of the polymers being analyzed. The stationary phase consists of porous beads that have a specific pore size distribution, which allows for the separation of polymer chains based on their size.3. Selection of the mobile phase: Choose a suitable mobile phase solvent that is compatible with both the stationary phase and the polymer sample. The mobile phase should dissolve the polymer without causing swelling or shrinking of the stationary phase. Common solvents used for SEC include tetrahydrofuran THF , dimethylformamide DMF , and water.4. Calibration of the system: Run a series of polymer standards with known molecular weights through the SEC system to generate a calibration curve. This curve will be used to determine the molecular weight of the unknown polymer samples based on their elution volumes.5. Sample injection and analysis: Inject the prepared polymer sample into the SEC system and allow it to pass through the column. The polymer chains will separate based on their size, with larger chains eluting first and smaller chains eluting later. Monitor the elution of the polymer chains using a suitable detector, such as a refractive index RI detector or a UV-Vis detector.6. Data analysis: Analyze the resulting chromatogram to determine the elution volume of each polymer chain. Use the calibration curve generated in step 4 to convert the elution volumes to molecular weights. Calculate the molecular weight distribution by plotting the molecular weight against the relative intensity or concentration of each polymer chain.7. Interpretation of results: The molecular weight distribution obtained from the SEC analysis provides valuable information about the polymer sample, such as the number-average molecular weight Mn , weight-average molecular weight Mw , and polydispersity index PDI . These parameters can be used to assess the quality, performance, and application potential of the polymer material.By following these steps, size-exclusion chromatography can be effectively used to determine the molecular weight distribution of polymers, providing crucial information for polymer scientists and engineers.