Polymers (Daniel Tice)

Title: Polymerization and Depolymerization

Quickwrite

Principle(s) Investigated: Polymerization, cross-linking, solvents, solubility, depolymerization

Standards :

Chemistry

10.a.Students know large molecules (polymers), such as proteins, nucleic acids, and

starch, are formed by repetitive combinations of simple subunits.

b.Students know the bonding characteristics of carbon that result in the formation of

a large variety of structures ranging from simple hydrocarbons to complex poly­mers and biological

molecules.

Materials:

Polymerization

• Guar gum powder (online or health food store)
• Borax powder (detergent aisle of Walmart)
• Water
• Containers
• Food coloring (optional)
• Ziploc bags

Depolymerization

• Styrofoam cups
• Acetone (paint aisle of hardware store)
• Container

Procedure:

Polymerization

1. Make borax solution by adding 1 tablespoon (~14 g) of borax powder to 1 cup (~237 mL) of water and mix thoroughly.
2. Make guar gum solution by adding 2 teaspoons (~10 g) of guar gum powder to 4 cups (~1 L) of warm water and stir slowly.
3. Add 1/2 cup (~119 mL) of guar gum solution to ziploc bag. Add 1 teaspoon (~5 mL) of borax solution to the same ziploc bag.
4. Seal the bag and shake vigorously.

Depolymerization

1. Fill container or bucket with about 5 - 8 cm of acetone.
2. Take any Styrofoam product and place in the solution.
3. Continue to push foam down into acetone to ensure proper depolymerization.

Student prior knowledge: Students should know about solvents and solubility. They should also know about the properties of liquids and solids.

Explanation:

Polymerization

Styrofoam is essentially a polymer that consists of interlinked chains of styrene molecules. However, the polystyrene consists of air pockets which make up about 95% of the total volume. When the styrofoam is placed in the organic solvent, acetone, the linkages that connect the polystyrene chains are degraded. As a result, the air pockets are released and the volume of the polystyrene is drastically reduced. This is why it appears as if the styrofoam is being dissolved completely, but in reality the insoluable polystyrene is left in the acetone as a dense clump of styrene chains.

Questions & Answers:

1) How is polymerization important in the cell?

While there are many instances of polymers in the cell, the most important would have to be the formation of proteins. Each amino acid is linked by a peptide bond. These bonds are added by the ribosome. Since proteins have very specific shape and function, the polymerization of these amino acids becomes very crucial to the survival of the cell.

2) How does the air get trapped in the polystyrene molecules?

While the polystyrene is molten and under immense pressure, HCFCs (Hydrochloroflourocarbons) are dissolved into the solution. When the polystyrene is cooled and extruded, the HCFCs cause it to expand and increase in volume. This is what creates the "foam" in Styrofoam.

3) What in the world is guar gum?

Guar gum is a powder made from the ground up endosperm of the guar plant (Cyamopsis tetragonoloba). It is a natural thickening agent and has 8 times the water thickening potential of cornstarch. This product is gluten free, so it is a great cooking alternative for individuals with celiac disease. It has also been found to increase calcium absorption in the colon, so less of the supplement is needed in daily consumption.

Applications to Everyday Life:

1. The depolymerization of plastics and other waste is becoming a widely studied topic. There is a process called thermal depolymerization, where rubber and plastic waste is ground up and mixed with water. This mixture is then cooked under pressure and the depolymerization proccess occurs. The result is activated carbon char, oil, and volatile gases. The gases are used to power the plant and the oil is converted into gasoline
2. Polymers are used every day, and a specific polymer actually keeps babies dry and parents sane. These polymers are better known as liquid-absorbing crystals and they are found in disposable diapers. They are super absorbent polymers made to hold several times their weight in water.
3. One of the most important polymerization reactions is transcription. This is where DNA is converted into a single strand of mRNA. RNA Polymerase, which is so appropriately named, attaches to the DNA and breaks the hydrogen bonds holding the double helix together. It then replicates the coding strand and links the new ribonucleic acid molecules with phosphodiester bonds, which creates a new polymer strand.

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

Videos:

1. First trial attempted by myself