ExpandedPolystyrene: An Experiment for UndergraduateStudents The preparation of polystyrene as a laboratory experiment has been described many times. However, students always obtain an oily or a solid compound; they do not identify this material as the well-known polystyrene, which is one of the most eammonly usedpolymers, especially in its expanded form. We indicate here twoverv. simde procedures - ex~erimental . that allow easy preparation of expanded~polystyr&e. Mix 25 mL toluene and 20 mL styrene inaone-necked flask,fitted withacondenser. Add0.7 g of benzoylperoxide and Separation is achieved by pouring the heat the solution t o reflux far 40 min, as has been described in detail previou~ly.~ cooled crude reaction mixture into 75 mL methanol; polystyrene then separates either as a white solid or as an oil.
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Emanslon ot the Ollv Polvstvrene
Zlext, decant the solvent and transfer the oil to s tall. 250-mL beaker. h a v e this beaker in a vacuum dessieator I ' m approximately 1.5 h, under a water-pump vacuum. After 40-60 min most of the solvent is removed and the polymer will start to foam and swell it; i t may even fill the beaker. When this stage is reached, allow the polystyrene t o dry and to harden for an additional 0.5 h under vacuum. This will provide a nice expanded polymer, which may occupy 10 times its initial volume. The melting point is consistent with literature data.'
Expansion ot Solld Polystyrene Put approximately 1g of the dried solid (or of any commercial polystyrene) in a thick-wded test tube. Add drop by drop exactly the minimum amount of tetrahydrofuran (THFI2necessary to dissolve the powder. The polymer solution looks like a colorless varnish on the walls of the test tube. Connect the tube t o a water pump by means of a rubber cork and tubine. eets hiehlvviseous. After -. and brine the inside of the tube under vacuum. As the THF slowlv , evaoorates the varnish ., 2-3 min heat the vnrnishstrongly with anarrgun for an additronal2-3 min. When the last trauesof aolvenr are removed, the polymer suddenly expands, b~rornessolid, and fills the test tuhe. It can be removed from the tuhe elther with help id n spatula of by dissolving i t in acetone. ~
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' Armstrong, D.; Man. J. N.: Kyle, D.; Alak. A. J. Chem. Educ. 1985, 62 705, Hszardeous solvent: ll may contain peroxides!
Alexandre Felgenbaurn Denlse Scholler Univmsit6 de Reims F 51062 Reims Cedex. France
810
Journal of Chemical Education
