Materials Included In Kit

Additional Materials Required

Safety Precautions

Ethylene glycol is slightly toxic by ingestion, inhalation or skin absorption. Phthalic anhydride is irritating to the skin and eyes and is a skin sensitizer, especially after contact with water. It is slightly toxic by ingestion. Use only Pyrex^® or borosilicate glass test tubes, and check for cracks or chips before using the glassware. Avoid contact of all chemicals with eyes and skin. Work with volatile organic compounds in a fume hood or in a well-ventilated lab only, and avoid breathing the vapors. Perform Activity B in a well-ventilated lab only. Avoid skin and eye contact with any of the chemical reactants and products in the three activities as they may cause skin and body tissue irritations. The solution of hexamethylenediamine contains 0.5 M sodium hydroxide. It is a toxic and corrosive liquid. Sebacoyl chloride has a suffocating acid odor. Sebacoyl chloride and hexane are flammable liquids and fire risks—keep away from all flames and sparks. Perform Activity C in a hood or in a well-ventilated lab only and avoid contact of all chemicals with eyes and skin. Rinse the nylon thoroughly with water before handling and allow polyurethane foam to cure for at least five minutes before handling. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Save all reagents for future use—use the storage codes printed on the Flinn labels to properly store flammable organic chemicals. The precipitated polyester samples may be discarded in the solid waste according to Flinn Suggested Disposal Method #26a. The disposable cups from Activity B may be thrown in the trash. Any leftover reactants (starting materials) not saved for future use should be mixed together and allowed to react—the solidified polymer may be disposed of in the trash according to Flinn Suggested Disposal Method #26a. The nylon produced during the reaction should be rinsed with water and may be disposed of in the trash according to Flinn Suggested Disposal Method #26a. Make sure all of the organic reactants have been converted to polymer before disposing of the reaction mixture. Excess sodium hydroxide solution may be neutralized according to Flinn Suggested Disposal Method #10.

Lab Hints

• Enough materials are provided in this kit for 27 students working in groups of three or for nine groups of students. For best results, and to reduce the amount of hazardous chemicals used, set up three activity stations for each synthesis, and have students rotate through the stations to complete each activity. (The activities may be completed in any order.) Three stations for each activity will probably be sufficient for a class of 27 students working in groups of three to complete the activity within a 50-minute lab period. Down-time between stations may be used for students to work Prelab Questions as well as Post-Lab Questions.
• For the synthesis of polyester,steps 14 and 15 both begin with the word “slowly.” This is very important to avoid overheating the materials and possibly spraying or splattering the contents of the test tube.
• Although the foam from the polyurethane activity station will set within 5–10 minutes, it may contain unreacted material for up to 24 hours. Some people may have allergic reactions to the unreacted monomers.
• Do not use laboratory glassware to make polyurethane foam. The foam will stick to the glass and is impossible to remove. Acetone may be used to dissolve any polymer from the polyurethane activity station that has hardened on glassware or on the lab bench.
• Wash the nylon several times before handling the material.

Teacher Tips

• Most students do not truly understand (appreciate is not always the right word) the pervasiveness of polymers and polymer products in their lives. Discuss the names, structures and uses of common addition and condensation polymers. Have students research on the Internet recent production figures for the manufacture of polymers.
• Instruct the students to observe the properties of the mixture before pulling the nylon. The two solutions are immiscible and do not mix. A film of white or pink insoluble material forms at the interface between the two solutions.
• Nylon 6,6 may be prepared by substituting adipoyl chloride for sebacoyl chloride in the second solution.
  {11995_Tips_Equation_8}

Answers to Prelab Questions

Activity A

1. Read the Safety Precautions and the entire Procedure section. What are the main hazards involved in working with phthalic anhydride in this experiment?

   Phthalic anhydride is a sensitizer—contact with the skin may cause irritation or rashes. Wear chemical-resistant gloves and do not allow the chemical to come in contact with skin. Wash hands thoroughly with soap and water before leaving the lab.

2. Why do condensation polymers generally have lower molar masses than addition polymers?

   Addition polymers are formed via chain reactions in which many thousands of monomers may add to the growing polymer chain before chain termination occurs. This leads to very long polymer molecules, and the average molar masses of the polymers are very high. Condensation polymers are formed in a stepwise fashion, and the average size of the polymer molecules does not grow as fast. Thus in a condensation reaction, monomers may first combine to form dimers (two repeating units), and then dimers may combine to forms tetramers (e.g., four repeating units) Note: The following graph illustrates the difference.

Activity B

1. Read the Safety Precautions and the entire Procedure section. What are the main hazards involved in working with polyurethane foam system (Part A and Part B) in this experiment?

   Avoid skin contact—both reagents (Part A and Part B) may contain skin and body tissue irritants.

2. What reaction causes the foam to expand to 30 times its original volume?

   Water reacts with the diisocyanate to produce carbon dioxide gas. The gas expands and creates pores in the polymer product.

Activity C

1. Read the Safety Precautions and the entire Procedure section. What are the main hazards involved in working with hexamethylenediamine–sodium hydroxide solution and sebacoyl chloride/ hexane solution in this experiment?

   The solution of hexamethylenediamine contains 0.5 M sodium hydroxide. It is a toxic and corrosive liquid. Sebacoyl chloride has a suffocating acid odor. Sebacoyl chloride and hexane are flammable liquids and fire risks—keep away from all flames and sparks.

Sample Data

Activity A

Activity B

Answers to Questions

Activity A

1. Polymer solutions or polymer “melts” are generally viscous—thick and slow to pour. Why do polymers have higher viscosities than monomers or smaller molecules?

   The properties of the mixture changed. The hot liquid was very “thick” and the cooled product was a transparent solid. The physical properties indicate that a new compound was formed with a different composition than the starting material.

2. Glycerol reacts with phthalic anhydride to form a cross-linked polyester—several polymer “chains” are tied together into a three-dimensional network. Draw a diagram that shows why using glycerol instead of ethylene glycol produces a cross-linked polyester.

Glycerol has three reactive –OH groups, not just two, as in ethylene glycol. This means that glycerol can form ester groups with three phthalic anhydride molecules. The result is a “network” of connected monomer units, not just a long chain of repeating units. The lines or “arms” represent reactive functional groups in the following diagram.

Activity C

1. Describe what happened in this experiment. Include all observations you made about the substance produced.

   Student answers will vary.

2. Why does the nylon form only at the interface of the two solutions?

   The solvents hexane and 0.5 M aqueous NaOH are immiscible. The only place the reactants come into contact is at the interface of the solvents.

References

This experiment has been adapted from Flinn ChemTopic™ Labs, Volume 21, Polymers; Cesa, I. Ed., FlinnScientific: Batavia, IL, 2006.

Introduction

The list of polymers that we use every day is so long, and polymer products are so pervasive, that it is difficult to identify items that do not contain polymers. Polymers are used to make sandwich bags and milk bottles, disposable diapers and thermal insulation, nylon panty hose and acrylic sweaters, carpeting and vinyl floor tiles, bicycle helmets and basketballs, etc. Despite the tremendous variety of polymers and their properties, all polymers are basically made by either addition or condensation reactions. Use this set of three “mini-lab” activities to synthesize and study three of the most common and useful polymers—nylon, polyurethane and polyester.

Concepts

• Polymerization
• Condensation polymers
• Physical and chemical changes
• Catalysts

Background

Polymers are long, chain-like molecules composed of multiple repeating units of smaller molecules, called monomers, which have been joined together by a chemical reaction. All polymers can be classified into two main categories based on the nature of the chemical reaction by which they are made. Addition polymers are formed when organic compounds containing one or more C=C double bonds add to each other. Addition reactions typically require a catalyst to initiate the reaction, but once a reaction starts, it will continue as a chain reaction until thousands of monomer units have been added together. Condensation polymers are formed when monomers with different functional groups combine to form a new functional group. Condensation reactions usually generate a simple by-product, such as H₂O or HCl, which is split off when two functional groups combine. Condensation polymers are formed in a stepwise process and are usually smaller than addition polymers.

Activity A. Synthesis of Polyester

Polyesters are condensation polymers containing the ester functional group. The most common polyester is polyethylene terephthalate (PETE or PET), which is used to make beverage and other food containers, as well as synthetic fibers (Dacron^®) and films (Mylar^®). The ester functional group is obtained by condensation of an organic acid (RCO₂H) with an alcohol (R′OH), with water as a by-product (Equation 1). The structure of PETE and the monomers from which it is made are shown in Equation 2. Notice that both monomers contain two functional groups, one at each end. Without two functional groups in each monomer, a polymer chain would not form.

In this activity, a similar polyester will be formed by reaction of a carboxylic acid derivative called phthalic anhydride with ethylene glycol (Equation 3). Activity B. Polyurethane

There are many types of polyurethane, including fibers, coatings, elastomers, flexible foams and rigid foams. In this activity, a rigid polyurethane foam is produced by mixing equal parts of two liquids, referred to as Part A and Part B. The lightweight foam expands to about thirty times the original volume and hardens in about five minutes. Polyurethane foam is used in upholstery cushions, insulation, packaging and flotation devices. Part A is a viscous, cream-colored liquid containing a polyol, a surfactant and a catalyst. The polyol is polypropylene glycol [HO(C₃H₆O)_nH]. The hydroxyl (–OH) ends are the reactive sites in this material. A silicone surfactant reduces the surface tension between the liquids and the catalyst speeds up the reaction. Part B is a viscous, dark brown liquid containing diphenylmethane diisocyanate [(C₆H₅)₂C(NCO)₂] and oligomers (dimers, trimers or tetramers). When the polyol (Part A) is mixed with the diisocyanate (Part B), an exothermic polymerization reaction occurs, producing a polyurethane (Equation 4). In a secondary reaction, water reacts with the diisocyanate to produce carbon dioxide gas (Equation 5). The gas expands and creates pores in the polymer product. The multifunctionality of both reactants leads to a high degree of crosslinking in the product, causing it to become rigid within minutes. Activity C. Synthesis of Nylon 6,10

In 1939, the DuPont Company exhibited nylon, the world’s first synthetic polymer fiber, at the “World of Tomorrow” World’s Fair in New York City. Female models played tug-of-war with nylon stockings to demonstrate the unique properties of nylon—“as strong as steel, as fine as a spider’s web, yet more elastic than any of the common natural fibers!” What is nylon and how can nylon be prepared?

Nylon is a generic name for a family of polyamide polymers. Polyamides are condensation polymers obtained in the reaction of an organic acid with an amine. During a condensation reaction, a molecule of water is also formed as a byproduct (Equation 6). In order to obtain a polymer, the organic compounds must be difunctional, that is, they must contain a reactive functional group at each end of the molecule. Nylon is a very durable, water-resistant, strong and lightweight fiber. Sixty-five years after its discovery, nylon is still one of the most widely used synthetic fibers. Nylon is essential for camping and is used for tents, sleeping bags, climbing ropes and backpacks. It is also used in sails, parachutes, fishing nets and fishing line. Exercise clothing, windbreakers, socks and shorts, and of course “nylon” hose are all made from nylon. In the home, nylon is used for carpeting, luggage and most toothbrushes and hairbrushes. It is hard not to come in contact with this wonder fiber sometime during the day!

The various nylons are named by a numbering system that indicates the number of carbon atoms in the reacting units. The first number represents the number of carbons in the diamine and the second number represents the number of carbons in the diacid. Note that the diacid is usually replaced by a diacyl chloride (COCl) to make it more reactive. Nylon 6,10 is made from sebacoyl chloride and hexamethylene diamine (Equation 7).

Experiment Overview

The purpose of this “activity stations lab” is to investigate the condensation reactions needed to produce three common and useful polymers. There are three mini-lab stations set up around the classroom. Each activity focuses on a particular polymer and is a self-contained unit, with prelab questions, discussion, procedure and analysis. The activities may be completed in an order.

1. Polyester
2. Polyurethane
3. Nylon 6,10

Materials

Prelab Questions

Activity A. Synthesis of Polyester

1. Read the Safety Precautions and the entire Procedure section. What are the main hazards involved in working with phthalic anhydride in this experiment?
2. Why do condensation polymers generally have lower molar masses than addition polymers?

Activity B. Polyurethane

1. Read the Safety Precautions and the entire Procedure section. What are the main hazards involved in working with poly-urethane foam system (Part A and Part B)?
2. What reaction causes the foam to expand to 30 times its original volume?

Activity C. Synthesis of Nylon 6,10

1. Read the Safety Precautions and the entire Procedure section. What are the main hazards involved in working with hexamethylenediamine–sodium hydroxide solution and sebacoyl chloride/hexane solution in this experiment?

Safety Precautions

Ethylene glycol is toxic by ingestion, inhalation or skin absorption. Phthalic anhydride is irritating to the skin and eyes and is a skin sensitizer, especially after contact with water. It is slightly toxic by ingestion. Use only Pyrex or borosilicate glass test tubes, and check for cracks or chips before using the glassware. Avoid contact of all chemicals with eyes and skin. Work with volatile organic compounds in a fume hood or in a well-ventilated lab only, avoid breathing the vapors, and avoid skin contact—both reagents (Part A and Part B) may act as skin and body tissue irritants. Perform Activity B in a well-ventilated lab only. Avoid breathing any vapors Do not touch the foam until it has completely hardened (about 5–10 minutes). The solution of hexamethylenediamine contains 0.5 M sodium hydroxide. It is a toxic and corrosive liquid. Sebacoyl chloride has a suffocating acid odor. Sebacoyl chloride and hexane are flammable liquids and fire risks—keep away from all flames and sparks. Perform Activity C in a hood or in a well-ventilated lab only and avoid contact of all chemicals with eyes and skin. Rinse the nylon thoroughly with water before handling, and have students wash hands with soap and water after performing this activity. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.

Procedure

Activity A. Synthesis of Polyester

1. Obtain about 1 g of phthalic anhydride in a small weighing dish. Caution: Do not allow phthalic anhydride to come in contact with skin.
2. Tare (rezero) the balance with the weighing dish and phthalic anhydride and weigh about 0.05 g of sodium acetate into the mixture.
3. Carefully transfer the mixture of solids to a medium Pyrex test tube.
4. Using a glass Pasteur pipet, add about 0.5 mL of ethylene glycol to the test tube.
5. Using a plain-jaw (uncoated) buret clamp, attach the test tube to a ring stand at a 60° angle (see Figure 1). Make sure the mouth of the test tube is not facing you or your fellow students.
   {11995_Procedure_Figure_1_Preparation of a polyester}
6. Light a Bunsen burner and adjust the gas supply and air inlet to obtain a small flame (no more than 5 cm high). Caution: Make sure there are no open bottles of chemicals in the area of the Bunsen burner.
7. Slowly brush the burner flame across the bottom of the test tube to gently heat the contents. The mixture will melt and then begin to bubble as the ester forms. Do not place the test tube directly in the burner flame. Immediately remove the flame if the liquid boils too vigorously or if it starts to foam.
8. Slowly heat the test tube in this manner until the liquid turns pale yellow. Remove the burner flame and allow the test tube to cool for 2–3 minutes. Remove the clamp from the ring stand and pour the product into a paper cup or onto a piece of cardboard.
9. Allow the polymer to cool and harden, and record observations in the data table.
10. Dispose of the polymer products as directed by the instructor.

Activity B. Polyurethane

1. Pour approximately 20 mL of liquid Part A into a disposable plastic cup. Note: The exact volume is not critical. Add a few drops of food coloring, if desired, and stir thoroughly to mix.
2. Pour approximately 20 mL of liquid Part B into a second disposable cup.
3. Spread paper towels or newspaper on the table and place one of the cups in the center.
4. Pour the contents from the second cup into the cup on the paper towels and stir thoroughly until bubbles form and the mixture begins to expand. Remove the stirring rod and place it on the paper towels.
5. Carefully feel the sides of the cup and observe the signs of chemical change as the reaction proceeds and any physical changes that result.
6. Record detailed observations in the data table and identify any changes as physical or chemical. Be specific—there should be at least five or six “signs” of chemical and physical change.
7. Do not touch the foam until it is completely hardened.
8. Dispose of the polymer products as directed by the instructor.

Activity C. Synthesis of Nylon 6,10

1. Add 10 mL of the hexamethylenediamine–sodium hydroxide solution to a small beaker.
2. Add 1–2 drops of diluted red food coloring to the hexamethylenediamine solution until it is a pale pink color. (The pink color will make the nylon strands more visible.)
3. Using a disposable glass (Pasteur) pipet, slowly add 10 mL of the sebacoyl chloride (hexane) solution down the side of the beaker. Try not to mix the two solutions, and do not stir.
4. The two immiscible liquids will form separate layers in the beaker. The sebacoyl chloride/hexane solution will be the upper layer and the hexamethylenediamine aqueous solution will be the lower layer. Observe the formation of an insoluble white or pink film at the interface between the two solutions.
5. Open a large paper clip to form a hook, and insert the hooked end into the nylon film at the interface between the two liquids. Slowly pull the nylon out of the beaker—it should come out in the form of long, thin, wet-looking strands.
6. Wrap the nylon strand around a stirring rod. Slowly turn the stirring rod to remove the nylon from the beaker. Continue pulling until no more nylon is left in the beaker. (Reinsert the paper clip hook as needed to start new strands.)
7. Wash the nylon strands by rinsing with water several times, and lay the nylon strands on a paper towel to dry.
8. Test the properties of the nylon fiber. How strong is it? What solvents does it dissolve in?

Student Worksheet PDF

11995_Student1.pdf