Bulk Polymerization of Styrene
EQUILIBRATION OF CONSTANT
Fill a 250 mL beaker
1/3 full with oil and place a magnetic stirring bar in the beaker.
Heat the oil bath to
80 degrees C on a hot plate equipped with a stirring rotor.
In the interest of time, the oil bath may be turned on and equilibrated
prior to the beginning of the laboratory period.
PREPARATION OF STYRENE:
REMOVAL OF INHIBITORS IN STYRENE
Prepare the mini-column
by placing a small glass wool plug in the bottom of a Pasteur pipette and
fill it one-half full with alumina.
Place the mini-column
in a hood and add styrene drop wise to the top of pipette. It takes about
4 minutes to elute 2 mL of styrene. If it takes much longer than 4 minutes,
the styrene may be contaminated with some polymeric material and very little
monomeric styrene will be collected in a reasonable amount of time. A new
bottle of styrene should be substituted.
PREPARATION OF POLYSTYRENE
There are several options
available in this experiment. The effect of initiator concentration on
yield and molecular weight distribution can be determined by running identical
reactions using three different initiator concentrations. Each student
can be assigned all three concentrations or only one of the three variations.
The class results are then pooled to determine the effects of initiator
concentration on yield and molecular weight distribution.
Weigh 0.250 g of freshly
eluted styrene and 1, 2 or 4 mg of the initiator, AIBN, in a 10 x 75 mm
Cover the test tube(s)
with a rubber septum.
Place the test tube(s)
in the oil bath at the same time and record time and temperature.
Remove the test tubes
from the oil bath after 45 minutes.
Pour the reaction mixture
immediately after removal from the oil bath, into a beaker containing 20
mL stirred methanol. A white precipitate should settle out.
Continue to stir in
methanol for another 10-20 minutes.
Vacuum filter the solid
polymer and wash with methanol several times.
Air dry the polymer
or dry the polymer in a vacuum oven at room temperature until constant
Weigh and save the
polymer in a vial. Yields may be calculated on dried samples.
Plot % yield of polymer
vs. mg of AIBN and note the effect of initiator concentration on the yield
If the product is difficult
to pour, add a small amount of toluene (0.5 mL) to dissolve it and then
pour as described in 7 into 40 mL of methanol.
may be characterized by Infrared spectroscopic identification of a film
cast on a NaCl or Kbr plate and the molecular weight distribution may be
determined by TLC or GPC techniques.