Objective: The objective of this lab is to become familiar with
spectroscopic analytic techniques used in polymer analysis specifically IR and Raman 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.
We will run IR and Raman this week.
Materials:
Polymers that are available such as Polymethylmethacrylate
(PMMA) of 3 tacticities: "atactic", predominantly isotactic,
predominantly syndiotactic. Polybutadiene of
variable cis and trans content (from golf ball and super ball),
nylon, polystyrene, PET, polycarbonate, other polymers.
Procedure:
There are several ways to make samples for IR/Raman.
Genarally solid samples can be used. In order to avoid
burnout of the samples we grind the Raman samples to a powder
and put them in NMR tubes as a dry powder.
You can bring your samples from the reverse engineering lab to
this lab for characterization.
- 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.
- The same samples will be examined using transmission IR from
cast films and in KBR pellets.
- Thin films of h-chloroform solutions will be cast on
surfaces for attenuated total reflection IR measurements.
- 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.
- Make KBr pellets from ground PMMA samples and examine using
Transmission IR.
- The PET bottle sample from the DSC experiment will be
examined as will samples of HIPS and other samples.
Analysis:
- Identify as many bands
as possible in the IR spectra using group contribution
methods.
- From the IR spectra determine the triad tacticity of the
PMMA samples.
- Compare the IR spectra obtained by ATIR, Transmission IR
from films, Transmission IR from the solutions, transmission
IR from KBr pellets (if these were run).
- Do the same for the Raman spectra.
- Compare the Raman and IR spectra for the poybutadiene
samples and determine the cis and trans content for these
samples.
Questions:
- Compare the information that was obtained from Raman with
that obtained from IR in the determination of tacticity and
chemical composition.
- Compare the cost and complexity of the two measurements and
the flexibility of the sample preparation.
- Why might you want to know the triad tacticity of a polymer?
- What is the group contribution method for IR/Raman and why
is it advantageous for polymeric systems?
- 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 in Raman? What wavelength of
electromagnetic radiation is involved in the two techniques?
How do the two types of quantized transitions differ in energy
for the two techniques?
- Why is IR data plotted against wavenumber?
- Why was PMMA chosen for this experiment?
- If your sample contained water and you want to ignore this
background would you use Raman or IR spectroscopy? Why?
- Please add the quiz questions to the text of your writeup.