Gel permeation chromatography GPC , also known as size exclusion chromatography SEC , is a widely used technique to determine the molecular weight distribution of a polymer. The method separates polymer chains based on their hydrodynamic volume in solution, which is related to their molecular weight. Here are the steps to determine the molecular weight distribution of a polymer using GPC:1. Prepare the polymer sample: Dissolve the polymer in an appropriate solvent to obtain a homogeneous solution. The concentration should be within the recommended range for the GPC system being used.2. Choose the appropriate columns: Select a suitable GPC column or a series of columns with the appropriate pore size and particle size to cover the molecular weight range of the polymer being analyzed.3. Calibration: Run a series of narrow molecular weight distribution polymer standards with known molecular weights through the GPC system. These standards should cover the molecular weight range of the polymer sample being analyzed. Record the retention times or elution volumes for each standard.4. Generate a calibration curve: Plot the logarithm of the molecular weight of the standards against their retention times or elution volumes. Fit a curve to the data points, which will be used to convert the retention times of the polymer sample to molecular weights.5. Run the polymer sample: Inject the prepared polymer solution into the GPC system and record the chromatogram, which shows the detector response as a function of retention time or elution volume.6. Data analysis: Convert the retention times or elution volumes of the polymer sample to molecular weights using the calibration curve generated in step 4. This will give you the molecular weight distribution of the polymer sample.7. Calculate molecular weight averages: From the molecular weight distribution, calculate the number-average molecular weight Mn , weight-average molecular weight Mw , and polydispersity index PDI = Mw/Mn to characterize the polymer sample.By following these steps, you can determine the molecular weight distribution of a polymer using gel permeation chromatography.