1. Major Concepts Activity 19 Plastics are a part of a group of chemicals known as polymers, which are made of repeating molecules (called monomers) linked together. The chemical structure of a polymer affects their physical properties Substances react chemically in characteristic ways with other substances to produce substances with different chemical properties

2. Title: Modeling Polymers Activity 20

3. Models help scientists investigate the characteristics of systems. When might it be helpful to work with a model? –Architectural models: how a building will look –Computer models of processes that are not easily observed (digestion). –The model may not look like the object. –It must function like the process. –A model can use physical objects, a simple diagram, or a mathematical equation.

4. Vinyl Alcohol Molecular Model What represents the: –Atom –Molecule –Nucleus –Protons –Neutrons –Electrons –Bonds We need to use a simpler model: –To represent the structure of even a small polymer would require thousands of units linked together. –This large number necessitates the use of a model.

5. Read pg. B-42 Problem: How can you use models to represent changes that occur during a chemical reaction? Hypothesis/Initial Thoughts:

6. Paper Clip Model Each individual paper clip represents a monomer (one molecule). You will compare the behavior of the model monomer to that of a model polymer and a model cross-linked polymer. Compare what you observe in this activity with your observations in the last activity.

7. In this activity you will: Pour, Stir, and Pull –Monomers (Single Paper Clips) –Polymers (A Chain of Paper Clips) –Cross-Linked Polymers (Diagram in Book) Paper Clip Chain: Polymerization Model –Chemical bonds formed between monomers. –Polyvinyl Alcohol Model from last class

8. Procedure: Follow the procedure on pages B-43 to B-45 Data/Observation: MonomerPolymerCross-linked polymer Vinyl alcoholPolyvinyl alcohol (PVA)Cross-linked PVA Pouring Stirring Pulling Comparing Model Monomers and Polymers E

9. What did you notice? Pouring and Stirring become increasingly difficult because the cross- linked polymer bunches together and moves as a single unit. When the polymers are Pulled out of the cup, they tend to lift out as a chain or as a bunch.

10. How do you think you could make your model polymer even more solid? Create more bonds. We will now create another kind of model of polymers. A pair of students holding both hands will represent a double-bonded vinyl alcohol monomer. Put your backpacks under the table.

11. With the person next to you… Hold both hands and then start to walk around the room. You are a monomer. Now, form a bond with two more monomers (you should be a chain of 6 people) and walk around the room. You are a polymer. Cross-link the polymers chains. Walk around the room.

12. What effect did going from monomers to polymers have on your ability to move? Traveling in a monomer pair was much easier than as a polymer. The polymer chain is still fairly flexible. Cross-linked: the longer and more complex the chain, the slower the progress. –Cross-linked PVA.

13. Analysis Question #3 Transparency 20.1 Cross-Linking a Polymer What is the difference? Student Sheet 20.2, Polymers in Daily Life. –Circle the polymers you have seen or used in the past week.

14. Other models Monomer How could you show a polymer with this model? How could you model a cross-linked polymer?