Polymers Are Cool: 3 Recipes for Middle School - Eva Varga

Chemistry is great for making many useful products. It’s also good for making stuff that’s just fun to play with. One of my favorite chemistry units is on polymers.

A polymer is a large molecule, or macromolecule, composed of many repeated subunits. In other words, they are made up of many, many molecules all strung together to form really long chains.

In Greek, Poly- means “many” and -mer means “part” or “segment”.  Mono means “one”. So, monomers are the individual molecules that can join together to make a long polymer chain.

A single polymer molecule is made out of hundreds of thousands (or even millions!) of monomers. Not all molecules can link up in this way to form polymers, however.

The atoms that make up a polymer chain essentially line up and repeat all along the length of the polymer chain. For example, look at polypropylene:

Polypropylene is made up of just two carbon atoms repeated over and over again. One carbon atom has two hydrogen atoms attached to it, and the other carbon atom has one hydrogen atom and one pendant methyl group (CH₃).

In this example, the pendant group hangs from the carbon atom in the chain backbone. As you can see from the example, pendant groups usually repeat along the length of the chain as well.

But enough of the mumbo jumbo. Let’s get to the fun stuff. What is better than reading about chemistry? Doing the labs, of course!  Here are three tried and true recipes for polymers you can use in the classroom.

Polymer Recipes ~ Get Messy!

Basic Polymer Putty

This is a fun and easy polymer to make (and the one featured in the photographs).

Materials

• Elmer’s white glue
• Borax (find in the laundry detergent aisle of the store)
• Water
• Two bowls
• Food coloring (just for fun)

Procedure

1. In one bowl mix 1/2 cup (4 oz) glue and 1/2 cup water. Add food coloring if you want colored slime.
2. In the other bowl, slowly mix borax into 1 cup of water until the borax will no longer dissolve (this is a saturated solution).
3. Add the glue mixture to the borax solution, stirring slowly.
4. The slime will begin to form immediately; stir as much as you can, then dig in and knead it with your hands until it gets less sticky.  Don’t worry about any leftover water in the bowl; just pour it out.

The glue has an ingredient called polyvinyl acetate, which is a liquid polymer. The borax links the polyvinyl acetate molecules to each other, creating one large, flexible polymer. It will get stiffer and more like putty the more you play with it.

Store it in a plastic bag in the fridge, to keep it from growing mold.

A Firmer Polymer

This recipe makes a firmer, dryer slime that will even bounce if it is kneaded enough.

1. Mix 4 tsp. (20 ml) water with 5 tsp. (25 ml) Elmer’s or other white glue in a small bowl.
2. Add 1 tsp. (5 ml) talcum powder and stir until thoroughly mixed.
3. Add 1 or 2 tsp. (5 or 10 ml) saturated borax and water solution. Stir four a few minutes.
4. Remove the glob from the bowl and stirrer. Knead it for a while and it will become drier.

You will probably need to wipe off some of the excess moisture from your hands with a paper towel from time to time. Don’t be tempted to wipe the glob with a paper towel as it will only stick. You can add a little talcum to the surface if you are having trouble getting it dry enough. Store in a zip lock in the fridge.

Take a closer look at plastics & polymers

Super Slime

This slime is similar to the one above, but creates a less rubbery and more transparent slime. This is the real gooey deal! (This slime is non-toxic, but still keep these chemicals away from unsupervised children and wash your hands after playing with the slime.)

Materials

• Polyvinyl Alcohol (PVA)
• Borax
• Water
• Graduated cylinder or measuring cups and spoons
• Food coloring (just for fun)

Procedure

1. Make a 4% solution of polyvinyl alcohol: Stir 1.5 teaspoons (approx. 4g) of PVA into 1/2 C (approx 100 ml) of water in a large microwave-safe bowl. Cover the bowl and microwave for 1 minute, then stir. Microwave another 30 seconds and stir. Continue until all the PVA is dissolved. A slight film may have formed on top; you can remove that with a spoon. You can add food coloring if you want colored slime. Allow the solution to cool.
2. Make a 4% borax solution by stirring a little less than 2 teaspoons (approx. 4g) of Borax into 1/2 cup of water.
3. Pour the cooled PVA solution into a ziplock bag and add 2 teaspoons (10ml) of the borax solution.
4. Zip the bag and knead it until the chemicals are mixed into slime. Then scoop it out and play with it.

While water is a liquid made up of individual H2O molecules, polyvinyl alcohol is formed of long chains of connected molecules, making it a liquid polymer. The borax acts as a “cross-linker,” linking the individual PVA chains to each other. The borax molecules form hydrogen bonds with molecules present in the PVA chains. The partial positive charge of hydrogen atoms attracts the partial negative charge of oxygen atoms. Since hydrogen bonds are weak, they can break and reform as you play with the slime or let it ooze on a flat surface.

Your slime will last for a while if you seal it in a plastic bag and keep it in the fridge.

Learn how to dispel children’s Misconceptions in Chemistry & Physics.

Helpful Hints for Success with Polymers

Gel type glues

Over the past few years several brands of gel type glues have been introduced. Most of these make excellent slimes which are very elastic and have a nice color and consistency. I have personally experimented with Elmer’s School Glue Gel, but there are several similar products available from other manufacturers. Try substituting a gel glue in the Basic Polymer recipe, above.

Slime overly sticky or runny?

If your white glue or gel glue based slime is too sticky or runny, first try kneading it for a while. Working it in your hands will help to mix things up better, as well as remove some of the moisture. If it is still not quite right, mix 1 part borax with 10 parts water. Dunk the slime into this solution, remove and knead.

Precautions

• Polymers can wreak havoc with plumbing, so don’t throw them down the drain.
• Always wear a mask when mixing PVA.
• Use distilled water for all solutions for best results.
• Keep polymers away from anything they could damage. They can dry into fabric and the dyes can stain surfaces, including wood.
• Supervise small children when playing with polymers so they do not ingest any.
• Some people are allergic to Borax powder. Wearing rubber gloves when mixing should help.
• Polymers using Borax solutions work best if you pour the Borax solution into the other solution, rather than the other way around. Coloring should be added before the Borax.
• Use metric measurements whenever possible. This will make it simpler to experiment with different concentrations and ratios.

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