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
• 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
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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
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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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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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13
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
CH 2
HC
C
CH 3
H2C
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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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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
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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
O
on phthalic acid
C
OH
OH
C
O
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End of Chapter 10
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