Microscale Bulk Polymerization of Styrene

EQUILIBRATION OF CONSTANT TEMPERATURE BATH

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 test tube.
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.

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.

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 weight.
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 of polystyrene.

The polystyrene 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.