1. 15 15-1 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Introduction to Organic Chemistry 2 ed William H. Brown

2. 15 15-2 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Organic Polymer Chemistry Chapter 15

3. 15 15-3 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Organic Polymer Chem.  Polymer: from the Greek, poly + meros, many parts. Any long-chain molecule synthesized by linking together single parts called monomers  Monomer: from the Greek, mono + meros, single part. The simplest nonredundant unit from which a polymer is synthesized  Plastic: a polymer that can be molded when hot and retains its shape when cooled

4. 15 15-4 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Organic Polymer Chem  Thermoplastic: a polymer that can be melted and molded into a shape that is retained when it is cooled  Thermoset plastic: a polymer that can be molded when it is first prepared, but once it is cooled, hardens irreversibly and cannot be remelted

5. 15 15-5 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Notation & Nomenclature  Show the structure by placing parens around the repeat unit  n = average degree of polymerization

6. 15 15-6 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Notation & Nomenclature  To name a polymer, prefix poly to the name of the monomer from which the polymer is derived if the name of the monomer is one word, no parens are necessary for more complex monomers or where the name of the monomer is two words, enclose the name of the monomer is parens, as for example poly(vinyl chloride) poly(ethylene terephthalate)

7. 15 15-7 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Morphology  Polymers tend to crystallize as they precipitate or are cooled from a melt  Acting to inhibit crystallization are their very large molecules, often with complicated and irregular shapes, which prevent efficient packing into ordered structures  As a result, polymers in the solid state tend to be composed of ordered crystalline domains and disordered amorphous domains

8. 15 15-8 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Morphology  High degrees of crystallinity are found in polymers with regular, compact structures and strong intermolecular forces such as hydrogen bonds as the degree of crystallinity increases, the polymer becomes more opaque due to scattering of light by the crystalline regions  Melt transition temperature, T m : the temperature at which crystalline regions melt as the degree of crystallinity increases, T m increases

9. 15 15-9 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Morphology  Highly amorphous polymers are sometimes referred to as glassy polymers because they lack crystalline domains that scatter light, amorphous polymers are transparent in addition, they are weaker polymers, both in terms of their high flexibility and low mechanical strength on heating, amorphous polymers are transformed from a hard glass to a soft, flexible, rubbery state  Glass transition temperature, T g : the temperature at which a polymer undergoes a transition from a hard glass to a rubbery solid

10. 15 15-10 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Morphology  Example: poly(ethylene terephthalate) (PET) can be made with % crystalline domains ranging from 0% to 55%

11. 15 15-11 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Morphology  Completely amorphous PET is formed by cooling the melt quickly PET with a low degree of crystallinity is used for plastic beverage bottles  By prolonging cooling time, more molecular diffusion occurs and crystalline domains form as the chains become more ordered PET with a high degree of crystallinity can be drawn into textile fibers and tire cords

12. 15 15-12 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Step-Growth Polymers  Step-growth polymerization: a polymerization in which chain growth occurs in a stepwise manner between difunctional monomers  We discuss five types of step-growth polymers polyamides polyesters polycarbonates polyurethanes epoxy resins

13. 15 15-13 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyamides  Nylon 66 (from two six-carbon monomers) during fabrication, nylon fibers are cold-drawn to about 4 times their original length, which increases crystallinity, tensile strength, and stiffness

14. 15 15-14 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyamides  The raw material base for the production of nylon 66 is benzene, which is derived from cracking and reforming of petroleum

15. 15 15-15 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyamides  Adipic acid is in turn the starting material for the synthesis of hexamethylenediamine

16. 15 15-16 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyamides  Nylons are a family of polymers, the two most widely used of which are nylon 66 and nylon 6 nylon 6 is synthesized from a six-carbon monomer nylon 6 is fabricated into fibers, brush bristles, high- impact moldings, and tire cords

17. 15 15-17 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyamides  Kevlar is a polyaromatic amide (an aramid) cables of Kevlar are as strong as cables of steel, but only about 20% the weight. Kevlar fabric is used for bulletproof vests, jackets, and raincoats

18. 15 15-18 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyesters  Poly(ethylene terephthalate) (PET) is fabricated into Dacron fibers, Mylar films, and plastic beverage containers

19. 15 15-19 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyesters ethylene glycol is synthesized from ethylene terephthalic acid is synthesized from p-xylene, which is obtained from petroleum refining

20. 15 15-20 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polycarbonates

21. 15 15-21 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polycarbonates  Lexan is a tough transparent polymer with high impact and tensile strengths and retains its shape over a wide temperature range it is used in sporting equipment, such as bicycle, football, and snowmobile helmets as well as hockey and baseball catcher’s masks it is also used in the manufacture of safety and unbreakable windows

22. 15 15-22 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyurethanes  A urethane, or cabamate, is an ester of carbamic acid, H 2 NCH 2 CO 2 H they are most commonly prepared by treatment of an isocyanate with an alcohol  Polyurethanes consist of flexible polyester or polyether units (blocks) alternating with rigid urethane units (blocks) the rigid urethane blocks are derived from a diisocyanate

23. 15 15-23 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyurethanes the more flexible blocks are derived from low- molecular-weight polyesters or polyethers with -OH groups at the ends of each polymer chain

24. 15 15-24 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Epoxy resins  Epoxy resins are materials prepared by a polymerization in which one monomer contains at least two epoxy groups within this range, there are a large number of polymeric materials and epoxy resins are produced in forms ranging from low viscosity liquids to high melting solids the most widely used epoxide monomer is the diepoxide prepared by treating 1 mol of bisphenol A with 2 mol of epichlorihydrin

25. 15 15-25 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Epoxy Resins

26. 15 15-26 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Epoxy Resins

27. 15 15-27 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Chain-Growth Polymers  Chain-growth polymerization: a polymerization in which monomer units are joined together without loss of atoms. For example:

28. 15 15-28 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyethylenes

29. 15 15-29 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polyethylenes

30. 15 15-30 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Radical Chain-Growth  Among the initiators used for radical chain- growth polymerization are organic peroxides, which decompose as shown on mild heating

31. 15 15-31 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polymerization  Radical  Radical: a molecule or ion containing one or more unpaired electrons  Fishhook arrow  Fishhook arrow: a curved and barbed arrow used to show the repositioning of a single electron  To account for the polymerization of alkenes in the presence of peroxides, chemists propose a three-step radical chain mechanism

32. 15 15-32 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polymerization  Step 1: chain initiation Chain initiation: a step in a radical chain reaction characterized by the formation of radicals from nonradical compounds

33. 15 15-33 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polymerization  Step 2: chain propagation Chain propagation: a step in a radical chain reaction characterized by the reaction of a radical and a molecule to give a new radical Chain length, n: the number of times the cycle of chain propagation steps repeats in a chain reaction

34. 15 15-34 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polymerization  Step 3: chain termination Chain termination: a step in a radical chain mechanism that involves destruction of radicals

35. 15 15-35 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Radical Chain-Growth  The first commercial polyethylenes produced by radical polymerization were soft, tough polymers known as low density polyethylene (LDPE) LDPE chains are highly branched due to chain- transfer reactions because this branching prevents polyethylene chains from packing efficiently, LDPE is largely amorphous and transparent approx. 65% is fabricated into films for consumer items such as baked goods, vegetables and other produce, and trash bags

36. 15 15-36 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Radical Chain-Growth  Chain-transfer reaction: the reactivity of an end group is transferred from one chain to another, or from one position on a chain to another position on the same chain polyethylene formed by radical polymerization exhibits a number of butyl branches on the polymer main chain these butyl branches are generated by a “back-biting” chain transfer reaction in which a 1° radical end group abstracts a hydrogen from the fourth carbon back polymerization then continues from the 2° radical

37. 15 15-37 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Radical Chain-Growth

38. 15 15-38 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Polymerization  Propylene and other substituted ethylene monomers can also be polymerized under a variety of experimental conditions radical polymerization of propylene involves 2° radical intermediates to give polypropylene, with methyl groups repeating on every other carbon

39. 15 15-39 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Ziegler-Natta Polymers  Ziegler-Natta chain-growth polymerization is an alternative method that does not involve radicals Ziegler-Natta catalysts are heterogeneous materials composed of a MgCl 2 support, a group IVB transition metal halide such as TiCl 4, and an alkylaluminum compound

40. 15 15-40 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Ziegler-Natta Polymers Step 1: formation of a titanium-ethyl bond

41. 15 15-41 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Ziegler-Natta Polymers Step 2: insertion of ethylene into the titanium-carbon bond

42. 15 15-42 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Ziegler-Natta Polymers  Polyethylene from Ziegler-Natta systems is termed high-density polyethylene (HDPE) it has a considerably lower degree of chain branching than LDPE and, a result, has a higher degree of crystallinity, a higher density, a higher melting point, and is several times stronger than LDPE appox. 45% of all HDPE is blow-molded into containers with special fabrication techniques, HDPE chains can be made to adopt an extended zig-zag conformation. HDPE processed in this manner is stiffer than steel and has 4x the tensile strength!

43. 15 15-43 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Recycling Codes

44. 15 15-44 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. Recycling Codes

45. 15 15-45 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. End Chapter 15 Organic Polymer Chemistry