Objective: The objective of this lab is to become familiar with spectroscopic analytic techniques used in polymer analysis specifically IR and Raman spectroscopy and NMR spectroscopy. A background in electromagnetic radiation and Beer-Lambert's Law may prove helpful. The most common techniques are IR spectroscopy from solutions and films and proton NMR from polymer solutions. Since the department does not own an NMR spectrometer we will need to make special arrangements for the entire class to observe a sample being run in the chemistry department. Data from this measurement will be analyzed by the class.

Materials:
Polymethylmethacrylate (PMMA) of 3 tacticities: "atactic", predominantly isotactic, predominantly syndiotactic. Tetramethylsiloxane (TMS). Benzene.

Procedure:

1. 5% solutions of the PMMA samples with a trace amount of TMS (0.1%) in d-chloroform will be used to obtain proton NMR spectra.
2. The same samples will be examined using transmission IR from cast films and in KBR pellets.
3. Thin films of h-chloroform solutions will be cast on surfaces for attenuated total reflection IR measurements.
4. Thin solid sheets of the PMMA samples will be made by hot pressing small amounts of the samples in a Carver Press. These will be examined using transmission IR.
5. Make KBr pellets from ground PMMA samples and examine using Transmission IR.
6. The PET bottle sample from the DSC experiment will be examined as will samples of HIPS and other samples.

Analysis:

1. Identify all NMR bands, especially those associated with tacticity in the PMMA samples.
2. Identify as many bands as possible in the IR spectra using group contribution methods.
3. From the NMR spectra determine the triad tacticity of the PMMA samples.
4. From the IR spectra determine the triad tacticity of the PMMA samples.
5. Compare the IR spectra obtained by ATRIR, Transmission IR from films, Transmission IR from the solutions, transmission IR from KBr pellets.

Questions:

1. Compare the information that was obtained from NMR with that obtained from IR in the determination of tacticity and chemical composition.
2. Compare the cost and complexity of the two measurements and the flexibility of the sample preparation.
3. Why might you want to know the triad tacticity of a polymer?
4. What is the group contribution method for IR and why is it advantageous for polymeric systems?
5. Spectroscopic techniques generally rely on the presence of a quantized transition which leads to a narrow band of absorption of electromagnetic radiation. What quantized transition exists in IR and NMR. What wavelength of electromagnetic radiation is involved in the two techniques? How do the two types of quantized transition differ in energy for the two techniques?
6. Why is IR data plotted against wavenumber while NMR is plotted against a parameter called the chemical shift? What is the difference between these two parameters and why aren't both of the spectra plotted against wavelength or frequency?
7. Why was PMMA chosen for this experiment?
8. What is the purpose of a strong magnetic field in the NMR instrument? Why is a strong magnetic field not necessary in the IR instrument?