To determine the molecular weights of polymer samples A, B, and C, the following methods can be used:
1. Gel Permeation Chromatography (GPC) or Size Exclusion Chromatography (SEC): This method separates the polymer samples based on their molecular size. The samples are passed through a column filled with porous beads, and smaller molecules elute later than larger molecules. By comparing the elution times of the samples with known standards of known molecular weights, the molecular weight of each sample can be determined.
2. Viscometry: This method measures the viscosity of the polymer samples at different concentrations. The viscosity is related to the molecular weight of the polymer. By plotting the viscosity versus concentration and extrapolating to zero concentration, the intrinsic viscosity can be determined. The molecular weight can then be calculated using the Mark-Houwink equation.
3. Light Scattering (Static or Dynamic): This method measures the scattering of light by polymer molecules in solution. Based on the scattering pattern, the molecular weight and size distribution of the polymer samples can be determined. Static light scattering measures the intensity of scattered light at a fixed angle, while dynamic light scattering measures the fluctuations in scattered light over time.
4. Mass Spectrometry: This method involves ionizing the polymer samples and measuring the mass-to-charge ratio of the resulting ions. By comparing the mass spectra with known standards, the molecular weight of each sample can be determined.
Step-by-step solutions:
1. GPC/SEC:
- Prepare a GPC/SEC column and set up the instrument.
- Inject the polymer samples A, B, and C into the column.
- Run the samples through the column and collect the eluted fractions.
- Measure the elution times of the samples.
- Compare the elution times with those of known molecular weight standards to determine the molecular weight of each sample.
2. Viscometry:
- Prepare different concentrations of the polymer samples.
- Measure the viscosity of each sample at different concentrations.
- Plot the viscosity versus concentration.
- Extrapolate the plot to zero concentration to obtain the intrinsic viscosity.
- Use the Mark-Houwink equation to calculate the molecular weight using the intrinsic viscosity.
3. Light Scattering:
- Prepare a solution of the polymer samples.
- Set up a light scattering instrument (static or dynamic).
- Measure the scattered light intensity or fluctuations.
- Analyze the scattering pattern to determine the molecular weight and size distribution of each sample.
4. Mass Spectrometry:
- Ionize the polymer samples using a suitable ionization technique (e.g., electrospray ionization).
- Measure the mass-to-charge ratio (m/z) of the resulting ions using a mass spectrometer.
- Compare the mass spectra with known standards to determine the molecular weight of each sample.