Polymer Structure and Function

In this unit, students use the phenomenon of why certain materials (such as the materials that make up a baseball) are useful for a particular function to explore the relationship between matter and energy phenomena. In this lesson students manipulate the properties of a polymer bouncy ball by changing the amounts of reactants in a chemical reaction. This page highlights key parts of this lesson.

Science Background for Teachers:

Science background gives teachers more in-depth information on the phenomena students explore in this unit. Below is an excerpt from the science background on polymer structure and function.

Structure and Properties of Polymers

All polymers, including silk, Teflon, and nylon, share certain properties because they are all huge molecules, with hundreds and sometimes thousands of atoms per molecule. Their structure gives them unique properties. For example, polymers are so large that they become entangled with each other.

Because of this structure, polymers tend to be strong and resistant to breaking. In contrast, small molecules like water do not tend to get tangled with each other because each water molecule is separate from the other. Polymers also tend to be both light and strong, and also resistant to chemicals (which is why Teflon is a non-stick coating on cooking pans).

Another way of thinking about the structure of polymers is to picture a box filled with steel chains. Each chain is made up of hundreds of individual links, but the chains themselves are not connected to any other chain. In this example, each steel chain represents one polymer molecule, made up of hundreds or thousands of atoms (individual links).

If you were to reach into the box and grab a chain, you could pull out an individual chain. But now imagine that you add a lot of tiny magnets into the box. Those magnets would attract the steel chains, connecting the individual chains into one large mass of chains. If you were to reach into the box and grab a chain now, you would pull out the entire mass of chains.

Making Bouncy Ball Polymers

To understand how this applies to polymers, let’s look at a simple chemical reaction between school glue and a substance called sodium borate, which is common in detergents and cosmetics.

By itself, glue is a synthetic polymer made up of molecules of polyvinyl acetate. It is a sticky liquid. Sodium borate is a solid powder that can be dissolved in water. Remember that box of steel chains. The glue is like the steel chains, made up of long chains of molecules strung together.

When you dissolve sodium borax in water and then add it to the glue, it has the same effect as adding the magnets to the steel chains. The sodium borate molecules react with the molecules of polyvinyl acetate, bonding at random places on the polyvinyl acetate molecule chains. The result is a new substance that is made up of tangled, long, flexible, cross-linked chains that are stretchy and bouncy. The unique properties of the new polymer can be changed by using different amounts of any of the reactants.

Once a polymer bouncy ball is formed, it has properties that relate to its function. One common function is as a toy that can be bounced. The bouncier the ball is, the higher it will bounce. Scientists can manipulate the height a bouncy ball bounces by using different amounts of any of the reactants.

Bouncy Ball Energy System

When any kind of ball is dropped from the air to the ground, it forms an energy system with the ground. For example, imagine that you are holding a polymer bouncy ball above the ground. The ball has gravitational energy. The higher you hold the ball, the more gravitational energy it has. When you drop the ball, that gravitational potential energy transforms into kinetic energy. In a perfect system, the total amount of energy is conserved as it transforms from one form to another. In other words, however much gravitational energy the ball has, that same amount of energy will transform into kinetic energy as the ball falls to the ground. However, in the real world, the ball won’t bounce as high on the second bounce because some of the energy has transferred out of the system.

As the ball moves through the air, drag causes some of the gravitational energy to transfer out of the bouncy ball system. As the ball falls to the ground, it experiences drag as it moves through the air. The force of drag causes some of the ball’s energy to transfer out of the system. When the ball hits the floor, friction between the ball and the floor transfers some more energy out of the system. Finally, at the moment the ball hits the ground, some of the energy is transferred out of the ball as it transforms to sound energy, which is energy produced by sound vibrations moving through a substance in waves.

At the same time as the ball hits the ground, the ground pushes back on the ball. This is because of Newton’s third law, the action-reaction law. The force of the polymer bouncy ball hitting the ground causes the ball’s shape to change because it is made of flexible rubber. As a result, the bouncy ball’s kinetic energy transforms to elastic energy, similar to what happens to the baseball when it is hit by the bat. As the bouncy ball’s shape is restored, the elastic potential energy transforms back to kinetic energy and the ball bounces back into the air.

Supports Grade 8

Science Lesson: Exploring Polymer Structure and Function

Students explore the investigative phenomenon of why some sports balls bounce higher than others to investigate how the amount of reactants can influence the properties of the products in a chemical reaction. They connect the molecular structure of a polymer bouncy ball with its property of bounciness.

Science Big Ideas

  • Some chemical reactions produce polymers— large molecules that are made up of many smaller molecules bonded together in a repeating chainlike pattern. This structure affects the properties of the substance.
  • Polymers are so large that they become entangled with each other. The polymer molecules can slide past one another, but they are still connected together. Polymers tend to be strong and resistant to breaking because of this structure.

Sample Unit CTA-2
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Science Essential Questions

  • Why is Teflon a synthetic material?
  • Why is Teflon useful?
  • How does the structure of polymers relate to their properties?
  • How does the amount of sodium borate in a polymer bouncy ball affect its bounce height?

Common Science Misconceptions

Misconception: After a chemical reaction, the product is a mixture made up of the old substances, which still exist, and therefore is not a new substance.

Fact: Chemical reactions produce new substances because they break down the molecules that make up the reactants and rearrange them to form new substances.

Misconception: Energy can be used up.  

Fact: Just like mass, energy is always conserved. Energy transforms from one form to another, and can transfer into or out of objects or systems, but the total amount of energy is conserved.

Science Vocabulary

Element : a substance made up entirely of one kind of atom

Matter : everything that has mass and takes up space

Molecule : a combination of two or more atoms bonded together

Polymer : a large molecule made up of many smaller molecules bonded together in a repeating chainlike pattern

Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

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Discovering Teflon

One of the only surfaces that geckos can’t stick to is Teflon, the material used in cooking pans to make them non-stick. Teflon was first discovered by accident in 1938 by a scientist named Roy Plunkett.

Plunkett was trying to come up with a chemical to use in refrigerators. He decided to use a gas, which he stored in metal cans with a valve release (similar to hairspray cans today).

On the morning he tried to release the gas from the can, Plunkett realized he couldn’t get the gas out of the can. However, the can weighed the same as it had when the gas was added. Plunkett was curious as to what was going on. He cut open the metal can, and discovered that the gas had turned into a white powder that was unusually slippery.

Teflon is a Synthetic Polymer

Plunkett was intrigued. He tested the unknown white powder for its properties. He discovered that the white powder was heat resistant and had a low surface friction. This meant that most other substances wouldn’t stick to it. That white powder would later be named Teflon.

Without meaning to, Plunkett had produced a synthetic polymer. Polymers are large molecules that are made up of many smaller molecules bonded together in a repeating chainlike pattern. Polymers are all around us. DNA, spider silk, natural rubber, and protein are all examples of naturally occurring polymers. Plastics, nylon, acrylic, and Teflon are examples of synthetic polymers.

 

Polymer Structure and Function

Teflon is so slippery because of its structure. It is a molecule because it is made up of the elements carbon and fluorine. The fluoride atoms completely surround the carbon atoms so no other outside atoms can get near the carbon to react with it. It is this structure that makes geckos unable to stick to its surface.

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Properties of Polymers

All polymers, including silk, Teflon, and nylon, share certain properties because they are all huge molecules. They have hundreds and sometimes thousands of atoms per molecule. Their structure gives them unique properties.

For example, polymers are so large that they become entangled with each other. Think of one polymer molecule as a piece of cooked spaghetti. In a bowl of spaghetti, that one piece of cooked spaghetti gets tangled up with all of the other pieces of pasta. It is very difficult to separate one piece of spaghetti from the remaining pieces because the strands of spaghetti are tangled together.

Polymer molecules are arranged in a similar way. This structure gives polymers some of their distinctive properties. For example, polymers are elastic, similar to how rubber bands are elastic. They can also flow, similar to how Silly Putty can flow. These properties occur because the polymer molecules can slide past one another, but they are still connected together.

 

Hands-on Science Activity

In this lesson, students design an experiment to explore the phenomenon of how increasing the amount of sodium tetraborate in a polymer bouncy ball affects its bounce height.

Science Assessments

KnowAtom incorporates formative and summative assessments designed to make students thinking visible for deeper student-centered learning.

  • Vocabulary Check
  • Lab Checkpoints
  • Concept Check Assessment 
  • Concept Map Assessment 
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Science Standards

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Standards citation: NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.