Experiment 8 – Chem 276 – Fall Semester 2010 Page 1 of 5

Polymers

Introduction

A polymer is a gigantic chainlike molecule made by connecting many small molecules, known as monomers. The process by which polymers are formed is known as polymerization. Today our culture is inundated with polymers materials used in everything ranging from Ziploc baggies and cell phones to car parts and satellites. In fact, it would now be difficult to even imagine life without synthetic polymers. Polymers are so useful because scientists are able to develop and produce polymer materials with many different properties. A polymer can be rigid, flexible, transparent, opaque, hard, soft, elastic, stiff and resistant to chemicals. Scientists are able to manipulate the properties of a polymer by choosing which monomers are used and how these monomers are chemically connected.

One of the most remarkable and useful polymers known is Teflon, formed via polymerization of tetrafluoroethylene as shown below:

F F F F (NH4)2S2O8 F C CF3 High pressure 3 F F F F n Tetrafluoroethylene Teflon

Teflon is resistant to virtually all chemicals, forms a surface which is non-stick, and maintains these properties over a temperature range of -270 to 385 Celsius.

The building you are working in today, Malcolm Renfrew Hall, is named after a former UI chemistry professor who published the first paper on Teflon in 1946 and (with DuPont) introduced this useful material to the world. Prof. Renfrew still lives in Moscow and recently celebrated his 100’th birthday.

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Another example of a useful polymer is polystyrene. It is formed via polymerization of simple substituted benzene called styrene.

Tert-butyl benzoyl peroxide 2 H3C(H5C6)HC CH2 CH2CH2(C6H5) Heat n H2C Polystyrene Styrene

This type of polymerization is known as an addition reaction because two styrene monomers are added together resulting in the removal of the double bond. Both tert-butyl benzoyl peroxide and heat are needed to start this reaction. Polystyrene is a hard and transparent polymer which is ideal for food containers. Polystyrene can also be readily foamed to create packing material or thermal insulators. Styrofoam is the trade name given to foamed polystyrene.

A second type of polymerization reaction is known as a condensation reaction. In a condensation reaction two monomers react to form a polymer with the elimination of a small molecule (such as HCl). Nylon 6-6 is synthesized using a condensation polymerization reaction. The monomers adipoyl chloride and hexamethylene diamine react to form the polymer with the elimination of HCl as shown below.

O H N Cl n 2 + n Cl NH2 O hexamethylene diamine adipoyl chloride

O O O O

+ Cl C(CH2)4 C NH (CH2)6 NH C (CH2)4 C NH (CH2)6 NH2 n HCl n nylon 6-6

Your task today will be to prepare two polymers: polystyrene and Nylon 6-6. Take care to follow the procedure carefully as you will be graded on the quality of your final products.

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Procedure

Polystyrene

1. Fill a 250 mL beaker ¾ of the way full with sand and place on a hot plate in the fume hood to set up a 140 Celsius sand bath. 2. Measure 10 mL of styrene into a large test tube. 3. Add 10 drops of tert-butyl peroxybenzoate to the polystyrene and mix. 4. Place the mixture in the sand bath and heat. Does the mixture change color during reaction? 5. Once you begin noticing bubbles, remove the test tube from the sand bath. Do not over heat. When the bubbles are no longer are forming, place the test tube back into the sand bath. Again remove test tube if the solution begins to bubble. 6. Continue heating until the mixture is syrupy in consistency. 7. Pour the syrupy mixture onto a watch glass and allow it to solidify. 8. The test tube can be brought to LabServices and be exchanged for a new test tube. 9. Peel the polystyrene from the watch glass and note its physical properties.

Nylon 6-6

1. Into a 50 mL beaker add 2 mL of 20% NaOH and 10 mL of a 5% aqueous solution of hexamethylene diamine and mix. 2. Measure 10 mL of a 5% adipoyl chloride solution in cyclohexane. 3. Being careful not to mix, slowly pipet the 5% adipoyl chloride solution on top of the aqueous solution in the 50 mL beaker. 4. You should see two different liquid layers with nylon 6-6 being formed at the interface. 5. Using forceps grasp the nylon at the interface at its center and slowly lift the solid from the solution. Lifting up to fast will cause the nylon to break. 6. As the polymer is lifted begin to roll the nylon around a stir rod. New nylon will continue to form at the interface. (Try to get at least a three foot piece.) 7. Wash the nylon with cold water and dry with paper towels. 8. Note the physical properties of the polymer.

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Report/Questions:

1. Show your polymers to your TA. You will receive a grade for the overall quality of both of your products.

Polystyrene ______/3

Nylon 6-6 ______/3

2. Describe the characteristics of each polymer:

a) Polystyrene

b) Nylon 6-6

3. What would occur if you overheated polystyrene?

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4. Styrofoam cups are made of polystyrene. Compare the density of the polystyrene you made with the density of a Styrofoam cup. How do we account for the difference in density?

5. Show the complete arrow-pushing mechanism for the base catalyzed condensation reaction to form the amide bonds of Nylon 6-6.