Playing with Polymers

What can glue teach you about molecules?: Stick with this activity, and you'll make your own bouncy polymers at home. Image: iStockphoto/klosfoto

Key concepts
Chemistry
Polymers
Ratios
Mixtures

Introduction
Have you ever wondered how fun toys like Silly Putty, Gak and Slime are made? It's the properties of polymers, certain kinds of large molecules, that make these products bouncy, slimy, stretchy, breakable, hard, soft, sticky, moldable?and just plain fun to play with.

Polymers are found in a variety of materials that have a broad range of properties. Materials made from polymers can be found in nature, such as amber and natural rubber, or generated synthetically, such as nylon, silicone and all plastics. The unique physical and chemical properties of polymeric materials can change depending on the amount of each different ingredient used to make them. How will changing the ratio of ingredients affect how a polymeric material feels and behaves?

Background
You can make a polymer-based material similar to Silly Putty at home by mixing together water, borax and Elmer's Glue. Elmer's is made up of polyvinyl acetate, which is a synthetic polymer. A polymer is a long molecule that is mostly made up of many similar repeating units. In the case of polyvinyl acetate, each repeating unit contains an acetate group. Borax, which is a white powder made up of sodium tetraborate, can react with this acetate group. Specifically, one molecule of borax can react with acetate groups on two different polyvinyl acetate molecules (such as those from the glue), creating a bond between the two polyvinyl acetate molecules.

Borax cross-links the polyvinyl acetate molecules together. The more cross-linked molecules, the larger the polymeric material that is made from the reaction. Additionally, as more cross-links are made, the more the polymeric material becomes less liquidlike and gains solidity.

Materials
Three zip-top bags
Water
Elmer's white school glue
Borax (also called 20-Mule Team Borax household cleaner)
Measuring cups
Measuring tablespoons and teaspoons
Two glass jars with lids
Permanent marker
Gloves, latex or similar style exam glove (optional)
Goggles or other eye protection

Preparation
??? ?Children should wear goggles or other protective eyewear, and adults should supervise and use caution when handling borax because it can irritate eyes.
??? ?In one glass jar add three tablespoons of water and three tablespoons of Elmer's Glue. Tightly secure the jar lid and shake it until the glue is fully diluted and no gooey clumps remain. Label this jar "Solution #1: 50 Percent Glue."
??? ?In the second glass jar, add one half cup of warm water and one teaspoon of borax. Again, tightly secure the lid and shake it until no particles of borax remain and the solution is clear. Label this jar "Solution #2: 4 Percent Borax."
??? ?The polymer material made in this activity can be sticky, so it should be kept off of clothing, wood and other rough surfaces that can be hard to clean. Also, the 50 percent glue solution and the glue?borax mixtures should not be poured down a drain because they can form clogs. Dispose of them in plastic bags.

Procedure
??? ?Take the three zip-top bags and label one "A," the next "B" and the third "C."
??? ?From the jar containing Solution #1 (50 percent glue) add one tablespoon to bag A, two tablespoons to bag B and three tablespoons and one teaspoon to bag C. After adding Solution #1 to each bag, carefully set the bags so they will not spill over.
??? ?From the Solution #2 (4 percent borax) jar add three tablespoons to bag A, two tablespoons to bag B and two teaspoons to bag C. Seal the bags closed.
??? ?What are the ratios of the two solutions that were added to each bag? Which bag contains the most glue, and which contains the least?
??? ?With the bags sealed closed, use your fingers to squish the mixtures around in each bag, mixing together the ingredients within the bag. Some bags may require more mixing than others. What do you observe happening within each bag? How are the resultant polymeric materials in each bag different from each other?
??? ?After a mixture has formed a sticky glob, you can take it out of the bag. What physical properties can you describe for each material you've made? Are some materials runny, slimy, sticky, hard, soft, bouncy, etcetera?
??? ?After investigating them, if you want to save your polymer products for later, put them back in their zip-top bags, seal them and store them in the refrigerator.
??? ?Extra: Are there other ways to change the recipe in order to change the physical properties of the polymeric product? Try changing the percentages of glue in Solution #1 or of the borax in Solution #2 to see how that changes your product. Can you optimize the recipe in a new and different way to obtain different types of products?
??? ?Extra: The protein gelatin found in Jell-O is also a polymer. What experiments could you conduct to explore the physical properties of other polymers, such as gelatin?

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