1. Polymers: Macromolecules
Chapter 21
Polymers: Macromolecules
The helmets protecting the
football players’ heads are
made of plastic, as are
many other parts of their
uniforms.
Introduction to General, Organic, and Biochemistry, 10e
John Wiley & Sons, Inc
Morris Hein, Scott Pattison, and Susan Arena 1

2. Course Outline 21.1 Macromolecules 21.2 Synthetic Polymers
21.3 Polymer Types
21.4 Addition Polymerization
21.5 Addition Polymers: Uses and Reuses (Recycling)
21.6 Butadiene Polymers
21.7 Geometric Isomerism in Polymers
Chapter 21 Summary 2 2

3. Macromolecules
What is a macromolecule? A macromolecule is a very large molecule consisting of repeating units called monomers.
Polymers are large molecules (sometimes referred to as macromolecules) composed of repeating units called monomers. 3 3

4. Macromolecules Polymers can be natural or synthetic.
Cotton is made of natural cellulose macromolecules
Microchips are made of synthetic macromolecules 4 4

5. Macromolecules
Other natural polymers are starch, silk, glycogen, and proteins.
The vast majority of the synthetic polymeric materials are based on petroleum (i.e. crude oil). A good example of this is polyethylene which is derived from ethylene. 5 5

6. Macromolecules
Ethylene (the monomer) can react with itself to form polyethylene or polythene (the polymer). Polyethylene is a long-chain hydrocarbon made from many ethylene units. 6 6

7. Macromolecules
A typical polyethylene molecule contains 2500 to 25,000 ethylene units joined in a continuous chain. 7 7

8. Synthetic Polymers
Chemists began to create large numbers of synthetic polymers in the late 1920s. Since then, ever-increasing numbers of synthetic macromolecular materials have transformed the modern world. Polymers are used extensively in nearly every industry.
Although there is a great variety of synthetic polymers they can be classified into the general groups based on their properties and uses shown on the next slide . . . 8 8

9. Synthetic Polymers
Although there is a great variety of synthetic polymers, based on their properties and uses, they can be classified into the following general groups.
1. Rubberlike materials or elastomers
2. Flexible films
3. Synthetic textiles and fibers
4. Resins (or plastics) for casting, molding, and extruding
5. Coating resins for dip-, spray-, or solvent-dispersed applications
6. Miscellaneous (e.g., hydraulic fluids, foamed insulation, ion-exchange resins) 9 9

10. Polymer Types
Polymers are can also be classified by how they are prepared. Although polymers often have complex structures, the underlying chemistry of polymerization is relatively simple.
There are two classes of organic reactions commonly used to prepare polymers . . . 10 10

11. Polymer Types
1. An addition polymer is a polymer that is produced by successive addition reactions. Polyethylene is an example of an addition polymer.
2. A condensation polymer is a polymer that is formed when monomers combine with the elimination of water or some other simple substance. This is a condensation reaction. Nylon is a condensation polymer. 11 11

12. Polymer Types
Polymers can also be classified based on their thermal properties. There are thermoplastic polymers and thermosetting polymers . . . 12 12

13. Polymer Types
1. Thermoplastic polymers soften when reheated. Polyethylene and polystyrene are examples.
2. Thermosetting polymers are infusible solids and do not soften when reheated. Phenolics (polymers made from phenol) are an examples. 13 13

14. Polymer Types
Thermoplastic polymers are formed when monomer molecules join end to end in a linear chain with little or no cross-linking between the chains.
Thermosetting polymers are macromolecules in which the polymeric chains are cross linked to form a network structure.
Figure 21.1 on the next slide shows the polymeric structures of thermoplastic and thermosetting polymers . . . 14 14

15. Polymer Types
Figure 21.1: Diagrams of thermoplastic and thermosetting polymer structures. 15 15 15

16. Your Turn!
What is the difference between addition polymerization and condensation polymerization? 16 16 16

17. Your Turn!
What is the difference between addition polymerization and condensation polymerization?
During condensation polymerization the polymer is formed in addition to water or other small molecule. The additional small molecules are not formed with the polymer during addition polymerization. 17 17 17

18. Addition Polymerization
In addition polymerization C=C bonds in the monomers react with other monomers until a long polymeric chain is formed as seen here.
Table 21.1 on the next slide shows polymers formed from modified ethylene monomers. 18 18

19. 19 19

20. Addition Polymerization
Many addition polymers are prepared by a free radical mechanism.
Free radicals are generated from a free radical source such as organic peroxides (general formula = ROOR). 20 20

21. Addition Polymerization
Free radical polymerization consist of three steps:
Free-radical formation
Propagation of the polymeric chain
Termination 21 21

22. Addition Polymerization
Step 1: Free-radical formation.
The organic peroxide splits into free radicals:
RO:OR  2 RO. 22 22

23. Addition Polymerization
Step 2: Propagation of Polymeric chain
A free radical adds to ethylene to form a new organic free radical. This free radical reacts with more ethylene to continue the growth of the polymeric chain.
RO. + CH2=CH2  ROCH2CH2.
ROCH2CH2. + CH2=CH2  ROCH2CH2CH2CH2.
ROCH2CH2CH2CH2. + CH2=CH2  RO(CH2CH2)n. 23 23

24. Addition Polymerization
Step 3: Termination
The chain stops growing when the organic free radicals react with each other to form stable molecules.
RO. + RO(CH2CH2)n.  RO(CH2CH2)nOR
RO(CH2CH2)n. + RO(CH2CH2)n. 
RO(CH2CH2)n (CH2CH2)nOR 24 24

25. Addition Polymerization
Ethylene can form low-density polyethylene (LDPE) molecules in the 20,000–40,000 molar mass range and high-density polyethylene (HDPE) in the 100,000s molar-mass range. 25 25

26. Your Turn! ROCH2CH2. + CH2=CH2CH2CH3 
Complete the free-radical addition equation showing propagation and termination steps starting with the following free radical and alkene.
ROCH2CH2. + CH2=CH2CH2CH3  26 26

27. Your Turn! ROCH2CH2. + CH2=CH2CH2CH3  ROCH2CH2CH2CH2CH2CH2.
Complete the free-radical addition equation showing propagation and termination steps starting with the following free radical and alkene.
Propagation
ROCH2CH2. + CH2=CH2CH2CH3 
ROCH2CH2CH2CH2CH2CH2.
ROCH2CH2CH2CH2CH2CH2. + CH2=CH2 
RO(CH2CH2)n. 27 27

28. Your Turn! RO. + RO(CH2CH2)n.  RO(CH2CH2)nOR
Complete the free-radical addition equation showing propagation and termination steps starting with the following free radical and alkene.
Termination
RO. + RO(CH2CH2)n.  RO(CH2CH2)nOR
RO(CH2CH2)n. + RO(CH2CH2)n. 
RO(CH2CH2)n (CH2CH2)nOR 28 28

29. Your Turn!
What are some common uses of polyethylene? 29 29

30. Your Turn! What are some common uses of polyethylene?
Packing materials, molded articles, plastic films, garbage bags, flexible bottles, containers and toys. 30 30

31. Your Turn!
Draw a three-unit portion of polypropylene. 31 31

32. Your Turn!
Draw a three-unit portion of polypropylene. 32 32

33. Addition Polymers: Use and Reuse (Recycling)
The addition polymers are the most common of all plastics. Over 50% of all polymers produced in the United States are made from ethylene and related compounds.
Approximately 15% of all landfill material is plastic. In the United States, about 30 million tons of plastic are thrown away each year. 33 33

34. Addition Polymers: Use and Reuse (Recycling)
Recycling is the first response to the problem posed by disposed plastics.
Successful recycling requires careful sorting of different plastics. The symbols on plastic goods are one step toward plastic identification and separation. 34 34

35. Addition Polymers: Use and Reuse (Recycling)
The identification codes for the most commonly recycled polymer are shown below. 35 35

36. Your Turn!
What does the “PP” stand for in the symbol below? 36 36

37. Your Turn! What does the “PP” stand for in the symbol below?
This is the identification code for polypropylene. “PP” stands for polypropylene. 37 37

38. Your Turn!
What does the “PS” stand for in the symbol below? 38 38

39. Your Turn! What does the “PS” stand for in the symbol below?
This is the identification code for polystyrene. “PS” stands for polystyrene. 39 39

40. Butadiene Polymers
A diene is a compound that contains two carbon–carbon double bonds. Another type of addition polymer is based on dienes like 1,3-butadiene and its derivatives. 40 40

41. Butadiene Polymers
Natural rubber is a polymer of isoprene (2-methyl-1,3-butadiene) which is also a diene. Many synthetic elastomers or rubberlike materials are polymers of isoprene and of butadiene. 41 41

42. Butadiene Polymers
Polymers of 1,3-butadiene and isoprene are shown below. Unlike saturated ethylene polymers, these polymers are unsaturated. They have double bonds in their polymeric structures. 42 42 42

43. Butadiene Polymers
One synthetic rubber (styrene–butadiene rubber, SBR) is made from the two monomers styrene and 1,3-butadiene. This polymer is a copolymer. A copolymer is made from two different monomers. 43 43 43

44. Butadiene Polymers
The presence of double bonds at intervals along the chains of rubber and rubberlike synthetic polymers makes vulcanization possible.
Vulcanization is the cross-linking of polymer chains with sulfur atoms. 44 44

45. Butadiene Polymers
The physical properties of rubber can be altered by vulcanization.
Vulcanization increases the abrasion resistance and the useful temperature range of the polymer. 45 45

46. Butadiene Polymers
In the segment of vulcanized rubber shown below, the chains of polymerized isoprene are cross-linked by sulfur–sulfur bonds, giving the polymer more strength and elasticity. 46 46 46

47. Your Turn!
Show one unit of a copolymer made from the monomers vinyl acetate and ethylene. 47 47

48. Your Turn!
Show one unit of a copolymer made from the monomers vinyl acetate and ethylene. 48 48

49. Your Turn!
Show three units of a polymer made from the following monomer by addition polymerization. 49 49

50. Your Turn!
Show three units of a polymer made from the following monomer by addition polymerization. 50 50

51. Geometric Isomerism in Polymers
The double bonds in isoprene and butadiene polymers allow for cis-trans isomers.
Recall that cis-trans isomers are molecules that differ only in the spatial orientation of their atoms.
For example an isoprene polymer can have all-cis, all-trans, or a random distribution of cis and trans configurations about the double bonds. 51 51

52. Geometric Isomerism in Polymers
Natural rubber is cis-polyisoprene with an all-cis configuration about the carbon–carbon double bonds.
The cis isomers give rubber molecules a “kinked” shape. 52 52

53. Geometric Isomerism in Polymers
Gutta-percha, also obtained from plants, is a trans-polyisoprene with an all-trans configuration.
The trans isomers give gutta-percha molecules a linear shape. 53 53

54. Geometric Isomerism in Polymers54 54

55. Geometric Isomerism in Polymers
Although these two polymers have the same composition, their properties are radically different.
The cis natural rubber is a soft, elastic material, whereas the trans-gutta-percha is a tough, nonelastic, hornlike substance. 55 55

56. Your Turn!
Draw the all-trans configuration of the polymeric fragment shown below. 56 56

57. Your Turn!
Draw the all-trans configuration of the polymeric fragment shown below. 57 57

58. Your Turn!
Draw the all-cis configuration of the polymeric fragment shown below. 58 58

59. Your Turn!
Draw the all-cis configuration of the polymeric fragment shown below. 59 59

60. Chapter 21 Summary Macromolecules commonly contain thousands of atoms.
A monomer is a small bonded group of atoms that forms polymers by reacting with other monomers. A polymer is a macromolecule made up of many monomers.
Polymerization is the chemical reaction that bonds monomers together to make a polymer.
Today many commercial products employ some synthetic polymers. 60 60

61. Chapter 21 Summary
An addition polymer uses an addition reaction to connect monomers together. A condensation polymer is formed when monomers bond together with a loss of water.
Thermoplastic polymers soften and can be remolded every time they are heated. Thermosetting plastics set to an infusible solid upon heating and do not soften upon reheating.
Addition polymerization is a free-radical chain reaction. 61 61

62. Chapter 21 Summary
Most synthetic addition polymers are not biodegradable. Recycling addition polymers seems to be the best means of decreasing plastic waste and reusing valuable organic molecules.
A butadiene polymer is an addition polymer made from 1,3-butadiene or its derivatives. Many elastomers (rubberlike polymers) are butadiene polymers.
A copolymer is made up of two different kinds of monomers. 62 62

63. Chapter 21 Summary
Polymers with double bonds commonly have geometric isomerism.
Natural rubber is an elastomer of all-cis polyisoprene, while gutta-percha is tough nonelastic material made from all-trans polyisoprene. 63 63