Chapter 20 Synthetic Polymers

1. Chapter 20 Synthetic Polymers

2. A polymer is a large molecule made by linking together repeating units of small molecules called monomers

3. Classification of polymers 1. Addition polymers(加聚物), also called chain-growth polymers, are made by chain reactions (链反应) 2. Condensation polymers(缩聚物), also called step-growth polymers, are made by combining two molecules by removing a small molecule

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5. 20-1. Addition polymers Chain-growth polymers proceed by one of three mechanisms: • radical polymerization • cationic polymerization • anionic polymerization

6. Some important chain-growth polymers and their uses

7. (1) Radical Polymerization

8. The molecular weight of the polymer can be controlled by a process known as chain transfer

10. Chain-growth polymerization of monosubstituted ethylenes exhibits a marked preference for head-to-tail addition Head-to-tail addition is favored for steric reasons Groups that stabilize radicals also favor head-to-tail addition

11. Examples of alkenes that undergo radical polymerization

12. Some radical initiators

13. Branching of the Polymer Chain Branched polymers are more flexible

14. (2) Cationic Polymerization Chain-initiating step Chain-propagating steps

16. The carbocation intermediates formed during polymerization can undergo rearrangement

17. Monomers that are best able to undergo cationic polymerization are those with electron-donating substituents Examples of alkenes that undergo cationic polymerization

18. Chain-propagating steps (3) Anionic Polymerization Chain-initiating step

19. Examples of alkenes that undergo anionic polymerization Monomers that are best able to undergo anionic polymerization are those with electron-withdrawing substituents

21. Ring-Opening Polymerization

23. Stereochemistry of Polymerization isotactic configuration (same side) 全同立构 substituents on the same side syndiotactic configuration (both sides) 间同立构 substituents regularly alternate on both sides atactic configuration (both sides) 无规立构

24. Stereochemical control of polymerization Long, unbranched polymers can be prepared using an aluminum–titanium initiator (Ziegler–Natta catalyst)

26. Natural and synthetic rubbers Natural rubber is a terpene (萜) Vulcanization (硫化): cross-linking of rubbers

27. Copolymer (共聚物) The product resulting from polymerization of different monomers is called a copolymer Some examples of copolymers and their uses

28. 20-2 Condensation Polymers (resin 树脂) Polyamides 聚酰胺 Polyesters 聚酯 Polycarbonates 聚碳酸酯 Polyurethanes 聚氨酯 Polyamides: Nylon 6

29. The incorporation of aromatic rings into polymers improves the physical strength of the polymers

31. Polyesters 聚酯

32. Polycarbonates 聚碳酸酯 热塑聚碳酸酯

33. Epoxy resins are the strongest adhesive known

34. polyurethane 聚氨酯

35. Thermosetting 热固性Polymers Very strong and rigid materials can be obtained by cross-linking

36. Oriented Polymers These polymers are stronger than steel They can conduct electricity

37. Biodegradable Polymers These polymers can be broken into small segments by enzyme-catalyzed reactions

38. Assignments • 26-2, 3, 5, 6