Polymer

Let's Explore

Purpose

To make a polymer.

Materials

• Masking tape
• Marker
• 2 1-pint (500-mL) jars
• 4-ounce (120-mL) bottle of white multipurpose school glue
• Tap water
• 2 mixing spoons
• 1 teaspoon (5 mL) borax powder (found near laundry detergents in the supermarket)
• 1-cup (250-mL) measuring cup
• 2 3-ounce (90-mL) paper cups
• 2-quart (2-L) bowl
• 12-inch (30-cm) -square piece of waxed paper timer

Procedure

CAUTION: As with any chemistry experiment, follow warnings on the containers of the materials used. Do not eat the glob produced.

1. Use the masking tape and marker to label the jars "Borax" and "Glue."
2. Pour the glue into the Glue jar.
3. Fill the empty glue bottle with water and pour the water into the Glue jar. Stir the glue and water to mix them together thoroughly.
4. Put the borax and 1 cup (250 mL) of water into the Borax jar. Stir, using a different spoon, until the borax dissolves.
5. Fill the paper cups, one with the glue-and-water mixture and the other with the borax-and-water mixture.
6. Pour the contents of each paper cup into the bowl, using either spoon to stir the mixture until it thickens.
7. Take the thickened substance called glob that forms out of the bowl and place it on the waxed paper for 1 to 2 minutes. Then remove the glob from the paper and knead it with your hands for about 1 minute.
8. Try these experiments with the glob and record your observations of how the glob responds in a data table:
   • Roll the glob into a ball and bounce it on a smooth surface.
   • Hold it in your hands and quickly pull the ends in opposite directions.
   • Hold it in your hands and very slowly pull the ends in opposite directions.

Results

You have made a soft, pliable (easily bent) material that spreads out when not confined, bounces slightly when dropped, breaks apart if pulled quickly, and stretches if pulled slowly.

Why?

In this experiment, a chemical reaction occurs when the reactants—borax, glue, and water—combine to form a cross-linked polymer called a glob. Cross-links are chemical bridges between two molecules. A polymer is a large, chainlike molecule made by combining many small single molecules called monomers. In this experiment, the borax forms bridges (cross-links) between the polymer chains in the glue much as the rungs of a ladder link the two sides together. The cross-linked polymer produced is much more viscous (thick; having a high resistance to flow) than the glue.

The glob has some properties of a solid—for example, it breaks when pressure is applied—and some properties of a liquid—for example, it flows. Sir Isaac Newton (1642–1727), an English scientist, described fluids (liquid or gas) as materials that flow under pressure. Since the glob flows, it is a fluid. But unlike the fluids described by Newton, the glob has some properties of a solid, so it is called a non-Newtonian fluid.

For Further Investigation

The cross-links make the glob less fluid than glue. Would more cross-links make the glob solid? A project question might be, How would the concentration of the reactants affect the fluid property of the glob?

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