Just for fun!
Why was nylon developed?
Nylon was originally developed for use in women's stockings. However, during World War II, virtually all nylon produced was used to make parachutes and tire cords. When nylon stockings returned to the market in 1945, there were "nylon riots" due to the limited supply. For more information, check out
Nylon: A Revolution in Textiles

Polymer Synthesis Lab¹

Goals

• Investigate the ability to synthesize and obtain sufficient yields of the polymer nylon 6.6
• Identify unknown recyclable plastics using the bonding characteristics of the polymers and infrared spectroscopy.

Background

I. Polymers

Organic chemistry is heavily involved in the production of many everyday items, such as, plastics, petroleum, and pharmaceuticals.  Polymers are any compounds with repetitive structural units, known as monomers, joined together like links in a chain.  Figure 1 shows some sample polymers with examples.

Figure 1: Examples of natural and synthetic polymers

II. Nylon 6.6

Nylon is another synthetic polymer that has yet to be profitable enough to recycle.  Therefore, it doesn’t fit into any of the recycle codes given in Table 1.  However, its synthesis is similar to the synthesis of several of the polymers listed in Table 2.  It’s obtained by joining lots of monomer units together of two distinct molecules: hexamethylenediamine and adipoyl chloride, as can be seen in Figure 2 below:

Figure 2: Synthesis of nylon 6.6

Nylon’s most important application is in the production of fibers for clothing, rope, and carpets.  Nylon behaves as a thermoplastic and can be melted and molded to fit any desired shape.  It’s used to make pipes, zippers, and wire insulation.  In this lab, you will be synthesizing nylon 6.6 in the form of a nylon rope.  Your synthesis would be the first step in many for a factory producing nylon commercially.  The factory would continue to heat and stretch your nylon rope until they obtained a very fine thread of nylon that could be used to produce a multitude of different clothes. 

In the synthesis of nylon 6.6, your two starting materials, hexamethylenediamine and adipoyl chloride, experience changes to specific bonds as they combine to create nylon 6.6.  These reaction sites are commonly referred to as functional groups.  Each functional group exhibits unique chemical properties.  Hexamethylenediamine is composed of two primary amines (RNH₂) (R indicates a carbon-containing group) and six alkane groups (-CH₂-).  When hexamethylenediamine reacts with adipoyl chloride (composed of two acid chlorides (RCOCl) and a similar 6 carbon alkane chain), the formation of a new functional group, an amide (R-NH-CO-), helps link these two molecules together.  This new dimer can continue to react with other amines and acid chlorides to produce a longer and longer chain of amide linked molecules until the one or both reactants are completely used up.  The amide linkage in nylon is exactly the same type of functional group created when amino acids link together to produce proteins.

Not only is the synthesis of nylon 6.6 a great demonstration of our ability to alter functional groups and obtain a new compound with new physical and chemical properties, but the molecules involved exhibit some unique chemical bonds that can be observed using infrared (IR) spectroscopy.  Every functional group exhibits very distinctive IR absorptions.  The IR absorptions can help us distinguish one type of bond from another.  Experimentally, you will be obtaining an infrared spectrum for your product (nylon 6.6) to help confirm that you synthesized nylon 6.6 and as mentioned earlier you will be able to identify an unknown plastic with infrared spectroscopy.  

Throughout this lab and the Computational Chemistry lab that follows, we hope to investigate the bonding characteristics of our molecules in the synthesis of nylon 6.6 and other plastics used in the world around us.  We will do this using hand-held molecular model kits and a computational molecular modeling software program known as Gaussian.  We will use IR spectroscopy to analyze our product and compare the various models we use to represent the bonding taking place in these molecules.

III. Identifying Polymers with Infrared (IR) Spectroscopy

Today, most synthetic polymers are able to be recycled, yet the wide range of possible polymers makes it more and more difficult to easily sort and recycle them.  The synthetic plastics have varied chemical and physical properties.  To help recyclers easily identify and sort the various plastics a coding system has been implemented as can be seen in Table 1. The chemical formulas for these polymers can be found in Table 2.

Table 1: Polymer recycle codes

Table 2: Structures of various polymers (http://en.wikipedia.org/wiki/International_Universal_Recycling_Codes)

If recyclers are unable to find the code on a specific piece of plastic, they can perform a variety of tests to determine the type of polymer present in the plastic.  One of these tests looks at the various types of covalent bonds present in the plastic using infrared spectroscopy.  From the monomer structures of the polymers given in Table 2, you can see the variety of different bonds that allow recyclers to distinguish one plastic from another.  Recyclers can also use the various densities and melting points of the plastics to help them determine their composition.  In this lab, we will identify an unknown plastic using infrared spectroscopy to help us identify the unique covalent bonds present in your unknown plastic.

IV. Infrared (IR) Spectroscopy

Infrared light is absorbed by most chemical matter. Whereas absorption of visible light usually results in the excitation of electrons, absorption of infrared light usually results in vibrations of bonds. Infrared Spectroscopy is a chemical identification technique in which infrared (IR) light is passed through a sample and a spectrometer identifies which frequencies of light have been absorbed by the sample. Different types of bonds absorb different frequencies of IR light, so analysis of an IR spectrum can tell you what types of bonds are present in your sample.

Table 3 gives the absorption values for certain bonds in the functional groups that you will be seeing in this lab.  Although a spectrum may contain extra peaks, a spectrum will always contain at least one peak for each type of IR-absorbing vibration present in a sample (IR is absorbed when a vibration results in a change of the dipole moment of the molecule). NOTE: A range of absorption values is given for each bond because the environment surrounding each bond can influence the exact infrared absorption value in the IR spectrum. 

Table 3: Characteristic IR absorptions of various polymers
Click to open a printable version of this table

V. Percent Yield

Reactions do not typically produce the predicted amount of product. Sometimes there are competing reactions. Sometimes the reaction is slow enough that the reaction does not complete within the timeframe of an experiment. Don't be surprised if you don't get 100% yield!

Synopsis of the Experiment

In Part 1 of the lab, you will synthesize nylon 6.6 and analyze your product by mass and by Infrared Spectroscopy. In Part 2 of the lab, you will identify unknown polymers using Infrared Spectroscopy.

Preparation

Reading Assignment:

• Description of experiment—see next page.
• Review Bonding—Zumdahl, Chapter 13 & 14.
• Review Stoichiometry & Percent Yield—Zumdahl, sec. 3.8, pp. 68-77.

Questions:

Fill out the prelab worksheet that can be found at the end of the Experiment section.

Experiment

To print instructions, select the portion that you with to print, choose File/Print, and choose "selection" to prevent printing the entire document.

Safety

• Wear safety glasses!
• Pour all waste solutions into the containers provided.
• Return unknown polymers to your instructor.

Materials and Equipment

ATR-FTIR Spectrum One Spectrometer

For Part 1: Synthesis of Nylon 6.6

• 2% (w/v) aqueous solution of hexamethylenediamine [C₆H₁₆N₂] containing 4% (w/v) sodium carbonate (Na₂CO₃) (2% w/v means 2g in a total of 100 mL)
• 2% (v/v) solution of adipoyl chloride [C₆H₈Cl₂O₂] in methylene chloride [CH₂Cl₂] (2% v/v means 2mL in a total of 100 mL)
• 50% (v/v) ethanol in water solution

For Part 2: Identification of Unknown Polymers

• Unknown polymers

Instructions

Students will work individually unless otherwise specified by your instructor.

Wear gloves when working with chemicals.

Part 1: Synthesis of Nylon 6.6 Rope

1. Put on gloves.
2. Pour 20 mL of a 2% (v/v) solution of adipoyl chloride in methylene chloride (CH₂Cl₂) into a 150 mL beaker. 
3. Using a different graduated cylinder, measure 10 mL of a 2% (w/v) aqueous solution of hexamethylenediamine. Slowly pour it on top of the adipoyl chloride solution.  (This solution will also have 4% (w/v) sodium carbonate to help increase the speed of the reaction.)
4. With the aid of tweezers pull the film that forms at the interface between the aqueous and organic layers and coil it around a glass rod held horizontally about 5 inches above the beaker. You may have a lump of nylon to start with. That's ok. If the lump is large, you may want to transfer it to a new beaker that will then become your collection beaker. If you get liquid bubbles, do not squeeze them, as they may spray liquid. 
5. With your fingers spin the glass rod to collect the nylon that keeps continuously forming at the interface as can be seen in Figure 3 below.

Figure 3: Setup for creating nylon 6.6 rope

5. Slide the nylon rope off your glass rod and into your collection beaker. In the beaker, wash the nylon rope with ~25mL water. Use your glass stirrring rod to break any bubbles in your rope. Lift your nylon and drain the water into a waste beaker. Wash the nylon rope again, this time with ~25mL of a 50% solution of ethanol in water. (Why do we use ethanol here?) Drain. You may now remove your gloves.
6. Dry your polymer with ~4 paper towels. Press the nylon firmly between the paper towels until there are no remaining bubbles. Continue pressing until the paper comes away completely dry. Leave your nylon to dry on a test tube rack in a hood for at least an hour.  
7. Before you clean up, look back at your reaction beaker and note observations. Has more nylon formed?
8. Before you leave lab, weigh your nylon 6.6 and obtain an FTIR spectrum of it.

Part 2: Identification of Unknown Polymer using Infrared Spectroscopy

1. Obtain an unknown polymer from your instructor.  Record the unknown number.
2. Obtain the unknown polymer’s infrared spectrum on the ATR-FTIR spectrometer. To save time, please print only one copy of the spectrum. You can make copies using the scanner in the back of lab. You will need copies for your lab notebooks as well as for your results.
3. Try to identify your unknown based on Table 3, above. To get some ideas as to what you polymer might be, start by looking for significant features in your spectrum, perhaps a strong peak (dips very low) around 1700 cm^-1 or double peaks around 1450 cm^-1. Then start eliminating polymers whose expected peaks are not present. Once you've identified your polymer, create and complete a table similar to Table 4 below, listing the expected absorbance ranges from Table 3 in column 2, and the corresponding peaks you observed in column 1.

Prelab & Results

Click here for Prelab worksheet: pdf or Word format

Click here for Results worksheet: pdf or Word format

References

¹Modified from Experimental Organic Chemistry; D.R. Palleros; 2000.

Intro Chem Lab Manual Home

Created By: Adilia James '07 and Sarah Coutlee '07
Maintained By: Nick Doe
Date Created: July 3, 2006
Last Modified: June 15, 2009
Expiration Date: July 3, 2009