Developers:

Stockton T. DuPont
C. E. Pickett Middle School
Philadelphia, PA

Noel G. Harvey
Plastic Research Department
Rohm and Haas Company
Bristol, PA

Topic Area:

"Glyptal Resin Plastic (Thermoset Polymer)"

Phthalic anhydride and glycerol are heated in a beaker. The clear plastic that is formed is poured into an aluminum cupcake tin. A penny (or some other object ) is placed in the cupcake tin and permanently embedded in the plastic. This experiment may be extended over several classroom periods.

Grade
Level:

7 and 8

Discipline:

Atomic Structure (molecular motion)

Goals:

1. To enhance the basic understandings for making "observations".
2. To gain a better understanding for collecting data.

Objectives:

1. Upon completion of this activity the students will demonstrate a knowledge of laboratory skills by:

   a. being able to identify a thermoset polymer and use laboratory equipment.
   b. using metric terms applicable to the apparatus being used.
   c. applying recognized safety rules to all laboratory work.
   d. being able to use observation skills previously taught.
   e. being able to chart and tabulate the data learned from the observation process.

    

2. Emphasis is on making accurate observations and measurements to qualify the various and varied observations.

Definitions:

Thermoset. A high polymer that solidifies or "sets" irreversibly when heated. This property is usually associated with a crosslinking reaction of the molecular constituents induced by heat or radiation, as with proteins, and in the baking of doughs. In many cases, it is necessary to add "curing" agents such as organic peroxides or (in the case of rubber) sulfur . For example, linear polyethylene can be crosslinked to a thermosetting material either by radiation or by chemical reaction. Phenolics, alkyds, amino resins, polyesters, epoxides and silicones are usually considered to be thermosetting but the term also applies to materials where additive-induced crosslinking is possible, e.g., natural rubber.

Background:

The reaction between glycerol and phthalic acid is basically an esterification. Water is produced during esterification and is removed by boiling the mixture. This plastic, glyptal resin, is a thermoset polymer; phthalic anhydride acts as a cross linker to hold strands of glycerol molecules together in a polymer.

Materials:

The teacher will procure the following items - a beaker, heat (hot plate, alcohol lamp, Bunsen burner) glycerol, phthalic anhydride, sodium acetate, goggles (safety glasses), and disposable gloves.

Procedure I:

Do this demonstration in a hood (proper ventilation); wear safety goggles and disposable gloves.

1.  
2. Place 20 grams of phthalic anhydride, 1.0 gram of sodium acetate, and 8.0 ml of glycerol into a small beaker.
3. Heat the beaker slowly (while stirring) to dissolve all remaining solids. Continue heating until the mixture boils for five minutes.
4. Prepare an aluminum cupcake tin by cleaning and drying.
5. Pour approximately half of the hot liquid into the aluminum cupcake tin.
6. Carefully place a penny (or some other coin) into the liquid in the aluminum cupcake tin. Then add the remaining liquid on top of the penny.
7. Let the plastic cool about 10 minutes at room temperature. Then place it on top of a container of crushed ice (or in a refrigerator) for further cooling.
8. Using scissors, strip away the aluminum to free the plastic with its embedded penny.

Noticeable
Observations:

1. The phthalic anhydride, in the mixture, when boiling will gather at the rim and sides of the beaker. This solid phthalic anhydride will be in a pure state.
2. The solid materials (phthalic anhydride and sodium acetate) become liquefied when heated with glycerol.
3. At room temperature, the mixture will not solidify if all of the water molecules are not evaporated.
4. When you place a container of the polymer in a freezer (for approximately 2 hours), the mixture will crack and become very brittle - easily cracked into many pieces or fragments.
5. During the esterification reaction, you will see bubbles produced by the formation of water.

Procedure II:

Follow the procedure in I but vary the heating time - 2, 4, 6, 8 minutes. Observe and record differences in the polymer.

Vocabulary:

Plastic Embedded Glyptal Thermoplastic

Polymer Molecule Glycerol Gram

Aluminum Mixture Phthalic Acid Milliliter

Thermoset Resin Ester Sodium Acetate

References:

1. Hawley's Condensed Chemical Dictionary, 11th Edition, 1987, Van Nostrand Reinhold, New York, page 1146.
2. This experiment was adapted from an experiment entitled" The Embedded Penny: Making Glyptal Resin Plastic" from the following book: Chemical Demonstrations, Vol I, by Lee R.Summerlin and James L. Ealy, Jr. (American Chemical Society, Washington, D.C. 1988.
3. The Everyday Science Sourcebook; Lawrence F.Lowery, Dale Seymor Publications, Palo Alto, CA 1985.

Questions
for Students:

1. When the reaction appears to boil, what substance is actually boiling off?
2. What is the function of the sodium acetate?
3. How does the structure of the phthalic anhydride molecule change in the esterification process?
4. How does the structure of glycerol change?

Extended
Activities:

The following experiment may be used to further enhance the student's understanding of making accurate observation and charting data observed.

A. Change the cooling time frame.

B. Change the method (crushed ice, refrigerator, freezer, room temperature only, etc.) of cooling.

Teacher Hints:

1. Perform activities yourself before assigning them to students to determine where students may have trouble.
2. Arrange the laboratory in such a way so that equipment and supplies are easily accessible to students. Avoid confusion where solutions and reagents are dispensed.
3. Have available only equipment and supplies needed to complete the assigned activity. This practice helps eliminate the problem of students doing unauthorized experiments.
4. Review the procedures with students and emphasize cautions found within the procedure. Give the students copies of the Material Safety Data Sheets on Phthalic anhydride, glycerol, and sodium acetate (readily obtainable from the supplier) and discuss safety.
5. Be sure all students know proper procedures to follow if an accident should occur.

The Glyptal Resin is a cross-linked thermoset, like connected spaghetti.

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