1. LESSON PLAN CROSSLINKING: THE KEY TO MAKING FAMLIAR AND SOME NOT SO FAMILIAR POLYMERS Father Judge High School Grade 9 Physical Science Mr. A. Gutzler

2. RATIONALE This lesson will be presented to first year high school students studying physical science At the time this lesson is presented they will have studied the structure of atoms, the periodic table and chemical bonding The RET experience will be connected through a lesson in the formation of polymers by a process called cross linking

3. PA STATE STANDARDS The following Pennsylvania State Standards apply to this lesson – 3.1.10.B: Unifying Themes: Concepts of Models as a Way to Predict and Understand Science – 3.1.10.E: Unifying Themes: describe Changes to Matter Caused By Heat or Chemicals – 3.2.10.C: Inquiry and Design: Apply the Elements of Scientific Inquiry to Solve Problems – 3.4.10.A: Explain the Formation of Compounds

4. OBJECTIVES Students will be able to construct models of monomers and polymers that show the relationship between these two classifications of molecules Students will understand how complex materials can be made by a process called cross linking

5. MATERIALS Jello powder PNIPAAm powder Jello gelatin Hydrogel 37 o C water bath Model kits Plastic bag

6. PROCEDURE 1. ACTIVATE PRIOR KNOWLEDGE Recall of previous material on states if matter, specifically gel. 2. ACTIVITY Students will build models of a monomer and a polymer using the model kits 3. DEMONSTRATE I can wrinkle the plastic bag and it returns to its shape. A bowl of Jello shakes but retains its shape This watery substance doesn’t look anything like the other two 4. SHOW Jello powder PNIPAAm powder 5. DEMONSTRATE Jello placed in a water bath liquefies BUT The other substance placed in the same bath becomes like Jello 6. QUESTION What might be the reason for this? What do students know about Jello? COLLECT RESPONSES Introduce the term hydrogel

7. PROCEDURE 7. POWERPOINT Through the slide on hydrogels 8. QUESTION – What are the similarities between Jello and the hydrogel? – Jello is also a cross linked polymer. Heat causes the cross linking – PNIPAAm is also a cross linked polymer but a chemical called PEG is the crosslinking agent. It establishes crosslinked chains of the monomer NIPAAm – KEY IDEA: BUT why does the PNIPAAm become a gel when heated while the Jello needs to be cooled to become a gel? – RECALL WHAT WAS SAID ABOUT HOT WATER AND JELLO – IS THERE A RELATIONSHIP BETWEEN WATER AND PNIPAAm?

8. ACTIVITY Let’s start with a monomer, ethylene – Build a model of ethylene using the molecular kit Here’s what they should make

9. ACTIVITY NOW MAKE POLYETHYLENE

10. CROSSLINKING Polymer chains such as polyethylene can move close to one another, form chemical bonds and result in materials with different properties It depends on the action of a material called a CROSS LINKING AGENT What kind of substance might result from the cross linking of polyethylene?

11. CROSSLINKING WHAT HAPPENS TO A POLYMER SUCH AS POLYETHYLENE DURING CROSS LINKING ?

12. OTHER EXAMPLES Jello is formed when polymer chains of collagen cross link by the action of HOT WATER Hydrogels can be formed by the cross linking action of OTHER MORE COMPLEX CHEMICALS

13. ASSESSMENT Using the model kits, can they make a monomer? Can they make a polymer? Can they build a cross linked polymer? Class develop and discuss a Concept Map showing monomer, polymer, gel and hydrogel

14. CROSS LINKED POLYMERS Three up close views of polymers What materials might these be?

15. FOLLOW ON ACTIVITIES The following links will be investigated in the computer room as a follow on activity Cross Linking – animation cross linking polymers - Google Search animation cross linking polymers - Google Search – O=CHem Polymers O=CHem Polymers The Science of Jello – http://infohost.nmt.edu/~mruth/posters/Jello%20revised.pdf http://infohost.nmt.edu/~mruth/posters/Jello%20revised.pdf Polymer Experiments – kids science information on polymers and states of matter kids science information on polymers and states of matter Experiment in Jello – http://engr.oregonstate.edu/momentum/k12/feb05/M!_GelBeads_fi nal021405.pdf http://engr.oregonstate.edu/momentum/k12/feb05/M!_GelBeads_fi nal021405.pdf