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
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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
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4. Some Naturally Occurring Polymers
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5. Celluloid React cellulose with nitric acid
Used for first films and billiard balls
Highly flammable
Used in smokeless gunpowder
No longer in use
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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
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7. Polyethylene Cheapest and simplest synthetic polymer Has two forms
Made from CH2=CH2
Invented shortly before World War II
Has two forms
High-density polyethylene (HDPE)
Low-density polyethylene (LDPE)
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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
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9. Polypropylene Change a –H to –CH3
Harder and has higher melting point than polyethylene
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10. Polystyrene Change a –H to benzene ring Widely used Disposable cups
Insulation
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11. Vinyl Polymers Change a –H to –Cl Tough thermoplastic
Polyvinyl chloride (PVC)
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12. Teflon Change all –H to –F C–F very strong. Resists heat and chemicals
Makes very unreactive polymer
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13. Other Polymers
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14. Practice Problems
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15. Rubber Pre–World War II Made of isoprene
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
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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
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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
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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
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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
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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
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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
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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
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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?
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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
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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
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27. Recycling Collect, sort, chop, melt, and then remold plastic
Requires strong community cooperation
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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
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