1. © 2014 Pearson Education, Inc. Synthetic Polymers Paula Yurkanis Bruice University of California, Santa Barbara Chapter 27

2. © 2014 Pearson Education, Inc. Polymerization A polymer is a large molecule made by linking together repeating units of small molecules called monomers.

3. © 2014 Pearson Education, Inc. A Chain-Growth Polymer (polystyrene) Chain-growth polymers (also known as addition polymers), are made by chain reactions.

4. © 2014 Pearson Education, Inc. Step-Growth Polymer (Dacron) Step-growth polymers (also called condensation polymers), are made by combining two molecules while removing a small molecule.

5. © 2014 Pearson Education, Inc.

6. Chain-Growth Polymers Chain-growth polymers are formed by one of three mechanisms. Radical polymerization Cationic polymerization Anionic polymerization

7. © 2014 Pearson Education, Inc. Radical Polymerization The initiator is a radical.

8. © 2014 Pearson Education, Inc. Propagation Steps

9. © 2014 Pearson Education, Inc. Termination Steps

10. © 2014 Pearson Education, Inc. Chain Transfer The molecular weight of the polymer can be controlled by a process known as chain transfer.

11. © 2014 Pearson Education, Inc. Head-to-Tail Linkage Chain-growth polymerization of monosubstituted ethylenes exhibits a marked preference for head-to-tail addition.

12. © 2014 Pearson Education, Inc. Poly(vinyl chloride) Head-to-tail addition forms a polymer with a substituent on every other carbon.

13. © 2014 Pearson Education, Inc. Stabilization of the Propagating Site Head-to-tail addition is favored for steric reasons. Head-to-tail addition is favored by groups that stabilize radicals.

14. © 2014 Pearson Education, Inc. Alkenes Used in Radical Polymerization

15. © 2014 Pearson Education, Inc. Radical Initiators

16. © 2014 Pearson Education, Inc. Branching of the Polymer Chain

17. © 2014 Pearson Education, Inc. Branched Polymers are More Flexible

18. © 2014 Pearson Education, Inc. Recycling Symbols

19. © 2014 Pearson Education, Inc. Cationic Polymerization The initiator is an electrophile.

20. © 2014 Pearson Education, Inc. Propagating Steps

21. © 2014 Pearson Education, Inc. Three Ways to Terminate the Chain

22. © 2014 Pearson Education, Inc. A Carbocation Monomer Can Undergo Carbocation Rearrangement

23. © 2014 Pearson Education, Inc. Alkenes Used in Cationic Polymerization Monomers with electron-donating substituents undergo cationic polymerization.

24. © 2014 Pearson Education, Inc. Anionic Polymerization The initiator is a nucleophile.

25. © 2014 Pearson Education, Inc. Propagating Steps Nonterminated chains are called “living polymers” and remain active until they are “killed.”

26. © 2014 Pearson Education, Inc. Alkenes Used in Anionic Polymerization Monomers with electron-withdrawing substituents undergo anionic polymerization.

27. © 2014 Pearson Education, Inc. Super Glue (an example of anionic polymerization)

28. © 2014 Pearson Education, Inc. What Determines the Mechanism? Alkenes with substituents that can stabilize radicals undergo radical polymerization. Alkenes with electron-donating substituents that can stabilize cations undergo cationic polymerization. Alkenes with electron-withdrawing substituents that can stabilize anions undergo anionic polymerization. Some alkenes undergo polymerization by more than one mechanism.

29. © 2014 Pearson Education, Inc. Ring-Opening Polymerization (anionic)

30. © 2014 Pearson Education, Inc. Ring-Opening Polymerization (cationic)

31. © 2014 Pearson Education, Inc. Stereochemistry of Polymerization Long, unbranched polymers with either isotactic or the syndiotactic configuration can be prepared using an aluminum–titanium initiator (a Ziegler– Natta catalyst).

32. © 2014 Pearson Education, Inc. Mechanism for Ziegler–Natta-Catalyzed Polymerization

33. © 2014 Pearson Education, Inc. Polymerization of Dienes These rubbers have cis double bonds.

34. © 2014 Pearson Education, Inc. Neoprene (a synthetic rubber) Neoprene has trans double bonds.

35. © 2014 Pearson Education, Inc. Disulfide Bonds in Rubber The more sulfur used in vulcanization, the more rigid the polymer.

36. © 2014 Pearson Education, Inc. Four Types of Copolymers

37. © 2014 Pearson Education, Inc.

38. Step-Growth Polymers The monomer can have two different functional groups. The monomer can be two different bifunctional compounds.

39. © 2014 Pearson Education, Inc. Step-Growth Polymerization Requires High Yields for Long Chains

40. © 2014 Pearson Education, Inc. Nylon is a Polyamide Nylon 6 is an example of a step-growth polymer formed by a monomer with two different functional groups.

41. © 2014 Pearson Education, Inc. Commercial Synthesis of Nylon 6

42. © 2014 Pearson Education, Inc. Nylon is a Polyamide Nylon 66 is an example of a step-growth polymer formed by two different bifunctional monomers.

43. © 2014 Pearson Education, Inc. Aromatic Polyamides are Called Aramides The incorporation of aromatic rings into polymers improves the physical strength of the polymers.

44. © 2014 Pearson Education, Inc. Kevlar

45. © 2014 Pearson Education, Inc. Dacron is a Polyester Polyesters are step-growth polymers in which the monomer units are joined together by ester groups.

46. © 2014 Pearson Education, Inc. Kodel is a Polyester

47. © 2014 Pearson Education, Inc. Lexan is a Polycarbonate Polycarbonates have two ester groups bonded to the same carbon.

48. © 2014 Pearson Education, Inc. An Epoxy Resin is a Cross-Linked Polymer (it is the strongest adhesive known)

49. © 2014 Pearson Education, Inc. A Urethane A urethane has an OR and an NHR bonded to the same carbonyl carbon.

50. © 2014 Pearson Education, Inc. A Polyurethane

51. © 2014 Pearson Education, Inc. Crystallites are Highly Ordered Regions

52. © 2014 Pearson Education, Inc. The More Crystalline the Polymer is, the Denser, Harder, and More Resistant it is to Heat

53. © 2014 Pearson Education, Inc. A Thermosetting Polymer Thermosetting polymers are cross-linked. The greater the degree of cross-linking, the more rigid the polymer.

54. © 2014 Pearson Education, Inc. An Oriented Polymer These polymers are stronger than steel and can conduct electricity.

55. © 2014 Pearson Education, Inc. A Plasticizer A plasticizer is an organic compound that is added to a polymer to make it more flexible.

56. © 2014 Pearson Education, Inc. Recycling a Polymer This is the reverse of the transesterification reaction that formed the polymer.

57. © 2014 Pearson Education, Inc. Biodegradable Polymers Polylactic Acid (PLA) Biodegradable polymers can be broken into small molecules by microorganisms.

58. © 2014 Pearson Education, Inc. PLA Cannot Be Used for Hot Drinks

59. © 2014 Pearson Education, Inc. Biodegradable Polymers (polyhydroxyalkanoates) Polyhydroxyalkanoates (PHAs) are condensation polymers of 3-hydroxycarboxylic acids.