7/30/2019 2410 lab polystyrene

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CHEM2410

Synthesis and Properties of Polystyrene

Safety notes:

Styrene is somewhat toxic; avoid breathing vapor or contact with skin. Benzoyl peroxide is unstable to heat andfriction and must be handled with care. Avoid contact with metal (transfer with a porcelain spatula) and prolonged

exposure to paper, cloth, or wood. Clean up all spills with water and rinse the glazed weighing paper with water after using.

Procedure:

 Removal of polymerization inhibitor 

Commercial styrene contains a phenol (often 4-tert -butylcatechol) as a polymerization inhibitor, which must be

removed before use in this experiment. Add around 3 mL of styrene to a test tube and add 3 mL of 10% NaOHsolution. Shake gently to mix the layers and use a Pasteur pipette to remove the aqueous (lower) layer. Repeat by

adding 3 mL of fresh 10% NaOH to the styrene, once again removing the lower layer. Make absolutely sure all of the lower (water) layer has been removed (even if you must sacrifice some of the top layer to do so). Dry the

styrene over anhydrous Na2SO4. This means add granular sodium sulfate to the styrene. As the sodium sulfate

 binds with any water that is present, it will clump. When you run out of water, then some of the sodium sulfate will

remain unclumped and the sample is dry. It takes several minutes for the sodium sulfate to bind the water so when

you think you are done, make sure you have given it a few minutes to potentially bind and clump.

Polymerization of styrene

Weigh about 1.0 g (record precise weight) of the purified and dried styrene into a separate test tube and add 5 mL of toluene to dissolve it. Obtain approximately 50 mg (this is 0.05 g) of benzoyl peroxide, add it to the 1 g of styrene

solution, and swirl the mixture to dissolve the peroxide. Label the tube and place it in a boiling water bath in the

hood for about 1 hour. Before the hour is completed, prepare another test tube with 5 mL of methanol in it.

Cool the sample to room temperature and add it dropwise (slowly!) and with swirling to the 5 mL of methanol in a

test tube. Mix well to coagulate the precipitate, which may adhere to the walls. Decant the slightly cloudy liquid

from the polymer and pour it into a waste solvent container. Add an additional 5 mL of methanol to the test tube

containing the polystyrene, stopper the tube with a foil-covered rubber stopper, and shake it vigorously.

Collect the polystyrene in a Buchner funnel, rinsing the test tube and the polymer into the funnel with another 5 mL

of methanol. After drying, weigh the polymer. Calculate the percent conversion (grams of polystyrene ÷ grams of styrene monomer).

Solubility tests:

Test the solubility of your polymer in acetone, water, and toluene by placing a few mg of polymer on a watch glass

and treating with a few drops of solvent. Be careful to note whether each solvent fully dissolved it or merelydispersed it somewhat.

Report

Calculate your yield and summarize your solubility results. Since the molecular weight of the product is simply a

multiple of the number of monomer units, your yield is the ratio of masses of product to reactant. Suggest a

structure of the polymer by drawing a portion of it carefully. Interpret your solubility results and explain why it

 behaved as it did. Identify the part(s) of the procedure that actually led to the most significant loss of yield and/or 

 purity.Answer each of the following:

1. Based on this understanding of the solubility, predict whether polystyrene will dissolve in ethanol?

2. Based on this understanding of the solubility, predict whether polystyrene will dissolve in benzene?

3. a. What are the expected results if the inhibitor is not removed?

 b. Suggest a way to obtain good results without removing the inhibitor.4. What are the expected results of adding twice as much benzoyl peroxide? Explain.