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Chapter 10 Polymers: Giants Among Molecules

Chapter 10 Polymers: Giants Among Molecules. Macromolecules. Compared to other molecules, they are enormous Molar mass: 10,000–1,000,000+ g/mol Not visible to naked eye Polymers: made from smaller pieces Monomer: small chemical building block

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Chapter 10 Polymers: Giants Among Molecules

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  1. Chapter 10 Polymers: Giants Among Molecules

  2. Macromolecules • Compared to other molecules, they are enormous • Molar mass: 10,000–1,000,000+ g/mol • Not visible to naked eye • Polymers: made from smaller pieces • Monomer: small chemical building block • Polymerization: process in which monomers are converted to polymers Chapter 10

  3. Natural Polymers • Found extensively in nature • Life could not exist without polymers • Come in various shapes and sizes • Made of sugars, amino acids, nucleic acids • Examples: wool, silk, cotton, wood, paper Chapter 10

  4. Some Naturally Occurring Polymers Chapter 10

  5. Celluloid • React cellulose with nitric acid • Used for first films and billiard balls • Highly flammable • Used in smokeless gunpowder • No longer in use Chapter 10

  6. Synthetic Polymers • Made from monomer synthesized from fossil fuels • First manufactured shortly before World War II • Synthesized using addition reactions • Add monomer to end of polymer chain • Build very large polymers Chapter 10

  7. Polyethylene • Cheapest and simplest synthetic polymer • Made from CH2=CH2 • Invented shortly before World War II • Has two forms • High-density polyethylene (HDPE) • Low-density polyethylene (LDPE) Chapter 10

  8. Thermoplastic and Thermosetting Polymers • Thermoplastic polymer: softened by heat or pressure and reshaped • Polyethylene • Thermosetting: harden permanently when formed • Once formed, cannot be reshaped Chapter 10

  9. Polypropylene • Change a –H to –CH3 • Harder and has higher melting point than polyethylene Chapter 10

  10. Polystyrene • Change a –H to benzene ring • Widely used • Disposable cups • Insulation Chapter 10

  11. Vinyl Polymers • Change a –H to –Cl • Tough thermoplastic • Polyvinyl chloride (PVC) Chapter 10

  12. Teflon • Change all –H to –F • C–F very strong. Resists heat and chemicals • Makes very unreactive polymer Chapter 10

  13. Other Polymers Chapter 10

  14. Practice Problems Chapter 10

  15. Rubber • Pre–World War II • Came from natural sources in S.E. Asia • Japan cut off supply during World War II • Made of isoprene • Chemists learned to make it during World War II Chapter 10

  16. Vulcanization • Link individual polymer strands with S atoms • Makes rubber stronger • Can be used on natural or synthetic rubber • Elastomers: materials that stretch and snap back • Key property of rubber Chapter 10

  17. Synthetic Rubber • Use butadiene • CH2=CH-CH=CH2 • Polychloroprene: substitute –Cl for a –H • Change the properties for other uses • Tend to be resistant to chemicals Chapter 10

  18. Copolymerization • Add two or more different monomers • Uses addition reaction • Allows for modification of polymer’s properties • Styrene–butadiene rubber (SBR) • 75% butadiene/25% styrene mix • Used mainly for tires Chapter 10

  19. Condensation Polymers • Part of the monomer will not be incorporated into the final material • Typically a small molecule like water • Formula of the repeating unit not same as monomer • Used to produce nylon and polyesters Chapter 10

  20. Composite Materials • Use high-strength polymers • Could include glass, graphite, or ceramics • Hold everything together with polymers • Typically thermosetting, condensation polymer • Result is a very strong, lightweight material • Used in cars, sports gear, boats Chapter 10

  21. Silicone Polymers • Based on alternating Si and O atoms • Heat stable and resistant to most chemicals • Properties depend on length of polymer • Many uses • Shoe polish, coatings on raincoats, Silly Putty Chapter 10

  22. Chapter 10

  23. Properties of Polymers • Crystalline: polymers line up • High tensile strength • Make good synthetic fibers • Amorphous: polymers randomly oriented • Make good elastomers • Some material has both types of polymers mixed together • Flexibility and rigidity Chapter 10

  24. Glass transition temperature, Tg • Above Tg, polymer is rubbery and tough • Below Tg, polymer hard, stiff, and brittle • Determine where polymer will be used • What type of Tg do you want your plastic coffee cup to be? Chapter 10

  25. Fiber-Forming Properties • Majority of fabrics made of synthetic polymers • Tend to last longer, easier to care for • Nylon vs. silk • Also may make mixtures • Cotton/polyester blends Chapter 10

  26. Disposal of Plastics • Do not degrade readily • Designed to be durable • Last a long time • Make up 8% by mass of landfills • But make up 21% by volume • Tend to fill up landfills • Incinerate plastics • Produce lots of heat when burned • May give off unwanted by-products • Degradable plastics • Photodegradable: need light to break down • Biodegradable: break down in presence of light • Do not want to degrade too soon Chapter 10

  27. Recycling • Collect, sort, chop, melt, and then remold plastic • Requires strong community cooperation Chapter 10

  28. Plasticizers • Make plastic more flexible and less brittle • Lower Tg • Tend to be lost as plastic ages • Most common plasticizers today based on phthalic acid Chapter 10

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