Polymer Chemistry 2011
Bulk polymerization of styrene with AIBN Step one: Preparation of the monomer. Remove inhibitors from styrene by passing it through a mini-column packed with basic alumina: place 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.
Step two. Polymerization of the monomer. 1. Weigh 2.5 g of freshly eluted styrene and 40 mg of the initiator, AIBN, in a 10 x 75 mm test tube 2. Cover the test tube with a rubber septum. 3. Place the test tube in a oil bath (60 ºC) and record time. 4. Remove the test tube from the oil bath after 45 minutes. 5. Pour the reaction mixture immediately after removal from the oil bath, into beakers containing 50 mL stirred methanol. A white precipitate should settle out. If the product is difficult to pour, add a small amount of toluene (2 mL) to dissolve it and then pour into methanol. 6. Continue to stir in methanol for another 10-20 minutes. 7. Vacuum filter the solid polymer and wash with methanol several times. 8. Air-dry the polymer or dry the polymer in a vacuum oven at room temperature until constant weight. Step three: Analysis of the polymer. Calculate the % yield of polymer. Record NMR of the sample, and run a differential scanning calorimetry to determine Tg. Questions/tasks: 1) Make a risk assessment. 2) Wright polymerization reaction scheme, identify the repeating unit 3) Wright detailed mechanism (initiation, propagation, termination) 4) Explain how the amount of initiator should affect the molecular weight of the polymer?
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