Experiment 5. Synthetic Polymers.
References: Solomons & Fryhle, Chapters 10, Special Topic B
INTRODUCTION:
A polymer (Greek: polys + meros = many parts) is a giant or macromolecule made up of repeating structural units. The reaction that unites small molecules called monomers (Greek: mono = one) into a polymer is called polymerization. Among the natural polymers important to life processes are starch and cellulose (monomer is glucose), proteins (monomers are amino acids), and nucleic acids (monomers are nucleotides, the phosphate ester of certain N-glycosides).
In this experiment, the preparation of several polymers in each of two main classes will be illustrated.
BACKGROUND:
Synthetic polymers can be categorized in several ways, one of which depends on their method of synthesis. Two main classes of polymers are addition polymers and condensation polymers.
PART A: Addition Polymers
Chain growth or addition polymers are formed by a reaction in which monomer units add to another with no other by-products. The most common type are vinyl polymers:
Individual units may be linked in a head-to-tail, head-to-head or random fashion. Examples of the many commercially important vinyl polymers include polyethylene (X=H), polypropylene (X=CH3), polystyrene (X = C6H5), polyvinyl chloride (X=Cl), polyvinyl alcohol (X=OH) or its acetate (X=OCCH3), as well as Teflon (the monomer is CF2 = CF2), and Lucite or Plexiglas (the monomer is CH2 = C(CH3)CO2CH3). Other functional groups, such as dienes, epoxides and aldehydes, can also self-unite to give addition polymers. Copolymers are prepared from the polymerization of a mixture of two or more monomers. Since the ratios of the monomers can be widely varied, copolymers for specific uses can be tailor-made.
PART B: Condensation Polymers
created in a separate step. This method gives long chains joined by many ester or amide links along with the elimination of some small molecule such as water, ammonia, or hydrogen chloride. Examples include Nylon (a polyamide), Dacron (a polyester), Bakelite, and polyurethane foams.
PART C: Solubility of Polymers
Different polymers tend to differ in their solubility and chemist can use this, along with physical properties, to identify certain polymers.
Using a flow chart similar to the one you will prepare (but more extensive), recycling centres can easily identify different polymers, if the recycling code is not visible.
PRE-LAB PREPARATION:
Read the experimental procedure so that you are prepared for the lab and you understand the safety and disposal information for the chemicals you are using in this experiment.
Review polymer reactions (Chapter 10 and Special Topic B), so that you have an idea of what to expect from this experiment.
1. Draw the structure of benzoyl peroxide and show how benzoyl peroxide decomposes to form two radicals (use curly arrows, etc.).
2. Two different radicals could be produced when an initiator radical adds to styrene. Show the structures of two radicals. Which one is preferred, and why?
3. Show the mechanisms (initiation, propagation and termination steps) for the formation of Polystyrene and for the formation of Poly(methyl methacrylate). The monomers are given below.
4. Show the mechanism for the formation of the polyester linkage (or bond) between phthalic anhydride and ethylene glycol, in slightly basic solution. What would occur if you use glycerol, instead of ethylene glycol (draw the product)? Starting materials are shown below.
EXPERIMENTAL PROCEDURE:
Safety and Disposal Data for Compounds used in Synthesizing Benzoic Acid.
Compound Mol. Wt.
(g/mol)
Safety and Disposal Data
Acetic Acid
10% Adipoyl Chloride (in hexane)
Benzoyl Peroxide Ethylene Glycol Formaldehyde Formic Acid Glycerol 5% 1,6- Hexanediamine Conc. (HCl) Hydrochloric Acid Methyl Methacrylate N,N-dimethylaniline Phenol Phthalic anhydride Sodium Acetate 10% Sodium Hydroxide (NaOH) Styrene Toluene 60.05 183.03 242.23 62.06 30.03 46.02 92.09 116.20 36.46 100.11 121.18 94.11 148.11 82.03 39.99 104.15 92.14
Corrosive. Flammable. Harmful if swallowed or inhaled. Dispose in ‘Inorganic Acids and Salts’.
Corrosive. Causes Burns. Lachrymator. Use gloves when handling. Dispose in Organic Waste.
Explosive. Irritating to eyes. May cause sensitization by skin contact. Use gloves when handling. If you need to dispose, contact your TA.
Harmful if swallowed. Dispose in Organic Waste.
Toxic. Flammable. Harmful by inhalation, in contact with skin and if swallowed. Lachrymator. Dispose in Organic Waste.
Corrosive. Harmful by inhalation, in contact with skin and if swallowed. Dispose in Organic Waste.
Avoid contact with skin and eyes. Dispose in Organic Waste.
Corrosive. Harmful by inhalation, in contact with skin and if swallowed. Dispose in Organic Waste.
Irritating to eyes, respiratory system and skin. Use gloves when handling. Dispose in ‘Inorganic Acids and Salts’.
Highly Flammable. Irritant. May cause sensitization by skin contact. Use gloves when handling. Dispose in Organic Waste.
Toxic. Dispose in Organic Waste.
Toxic. Causes burns. Dispose in Organic Waste.
Harmful by inhalation and if swallowed. Irritating to eyes and skin. Dispose in Organic Waste.
Avoid contact with skin and eyes. Dispose in Organic Waste.
Corrosive. Causes severe burns. Wear gloves when handling. Dispose in ‘Inorganic Bases’.
Flammable. Harmful by inhalation. Irritating to eyes and skin. Dispose in Organic Waste.
PART A: Addition Polymers
A1. Polystyrene
a) In a fume hood, add 0.1g benzoyl peroxide to 4.55g (5 mL) of styrene in a medium-sized glass test tube. Do not use the Pyrex test tubes (Pyrex test tubes have a rim on the endge of the
opening and they say Pyrex on the side). [Care: Do Not CRUSH the solid initiator]. b) Write your name on a little (9mm x 20mm) piece of paper with pencil and put it into the test tube.
c) Place the test tube in a beaker of boiling water (already boiling containing a few boiling chips) for over 1.5 hour.
d) Cool the test tube, and describe the polymer (colour, clear/opaque, stiff/flexible, brittle, solid/pellets/powder, etc.). You may have to break the test tube, but first wrap it in a paper towel (have your TA show you how this is done). Be careful with the broken glass. Use your forceps (not your fingers) to remove the pieces of glass from the polymer.
A2. Methyl Methacrylate Polymer
a) In a fume hood, add 1 drop of N,N-dimethylaniline and 0.03g of benzoyl peroxide to 5 mL of freshly distilled methyl methacrylate in a medium-sized glass test tube. Do not use the Pyrex test tubes (Pyrex has a rim and say Pyrex on the side). [Do Not CRUSH the solid initiator].
b) Write your name on a little (9mm x 20mm) piece of paper with pencil and put it into the test tube.
c) Place the test tube in a beaker of boiling water (already boiling containing a few boiling chips) for about 1.5 hour.
d) Cool the test tube, and describe the polymer (colour, clear/opaque, stiff/flexible, brittle, solid/pellets/powder, etc.). You may have to break the test tube, but first wrap it in a paper towel (have your TA show you how this is done). Be careful with the broken glass. Use your forceps (not your fingers) to remove the pieces of glass from the polymer.
PART B: Condensation Polymers
B1. Polyester
a) In a fume hood, place 2 g of phthalic anhydride, and 0.1 g of sodium acetate in each of two large-size glass test tube. Do not use the Pyrex test tubes.
b) To one test tube add 1 mL of ethylene glycol and to the other add 1mL of glycerol. Label the tubes using a grease pencil, do NOT put paper inside the test tube.
c) At the same time, place each test tube in the 2nd largest hole of an Aluminum heating block, which is being heated at ~200°C (do not need to use thermometer, make sure the tube starts boiling). Heat the test tubes for 25 minutes. This means that you will need both Al blocks (heated on the same hot plate) and will need to take turns with the other person in your fumehood. d) Cool the test tubes then describe (colour, clear/opaque, solid/pellets/powder, stiff/flexible, brittle, etc.) and compare the polyesters. You may have to break the test tube, but first wrap it in a paper towel (have your TA show you how this is done). Be careful with the broken glass. Use your forceps (not your fingers) to remove the pieces of glass from the polymer.
B2. Bakelite
a) In a fume hood, place 1.2 g of phenol, 3.5 mL of glacial acetic acid, and 1.5 mL of 37-40% aqueous formaldehyde solution in a test tube.
c) Cool the test tube in an ice bath and then place the test tube in the fume hood. Make sure your test tube has cooled to room temperature, then add 3.5 mL of conc. HCl to the test tube while still in the fume hood. Shake until you see the solid polymer starting to form and set aside to finish.
d) Cool the test tube, then dislodge and examine the polymer.
e) Describe the polymer (colour, clear/opaque, stiff/flexible, brittle, solid/pellets/powder, etc.).
B3. Nylon 6-6
NOTE: For this polymer, measure everything directly into your beaker. Don’t use your graduated cylinder, as the polymer will form in your graduated cylinder and is difficult to remove. Use the graduation on your beaker for approximate amounts.
a) Pour approx. 10 mL of 5% aqueous solution of 1,6-hexanediamine into a 100 mL beaker. Add 20 drops of 10% sodium hydroxide solution.
b) Tilt the beaker slightly, and carefully pour down the wall approx. 10 mL of a 5% solution of adipoyl chloride in hexane, trying to avoid mixing or turbulence.
c) A polymer film will form at the interface. Grasp this with a piece of hooked metal or pair of tongs. Fasten it to a large test tube or narrow beaker, and slowly rotate it, to draw out a polymer fibre.
d) Finally, rinse your fibre with water and dry it well with a piece of paper towel.
e) Describe the polymer (colour, clear/opaque, stiff/flexible, brittle, solid/pellets/powder, etc.). f) Once you have made all five different types of polymers, show them to your TA.
PART C: Solubility of Polymers
a) Place ~1 mL of toluene in one test tube and ~1 mL of formic acid in another test tube. b) Take a couple small pieces of a polymer and try to dissolve it in each of the test tubes. If you are unable to remove a piece of polymer, you can use someone else’s polymer or get your TA to smash your polymer for you.
