Chapter 10 Polymers: Giants Among Molecules
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Transcript of Chapter 10 Polymers: Giants Among Molecules
Chapter 10
Polymers: Giants Among Molecules
Chapter 10 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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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
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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
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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)
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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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Polypropylene
• Change a –H to –CH3
• Harder and has higher melting point than polyethylene
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Polystyrene
• Change a –H to benzene ring• Widely used
– Disposable cups– Insulation
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Vinyl Polymers
• Change a –H to –Cl• Tough thermoplastic
– Polyvinyl chloride (PVC)
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Teflon
• Change all –H to –F– C–F very strong. Resists heat and
chemicals– Makes very unreactive polymer
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Other Polymers
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Practice Problems
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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
CH2
CHC
H2C CH3
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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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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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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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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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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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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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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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• 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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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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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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Recycling• Collect, sort, chop, melt, and then
remold plastic• Requires strong community cooperation
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Plasticizers• Make plastic more flexible and less
brittle– Lower Tg
– Tend to be lost as plastic ages• Most common plasticizers today based
on phthalic acidC
OH
O
OHC
O