Transcript Chapter 10 Polymers: Giants Among Molecules

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
Chapter 10
2
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
3
Some Naturally Occurring
Polymers
Chapter 10
4
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
5
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
6
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
7
Polypropylene
• Change a –H to –CH3
• Harder and has higher melting point
than polyethylene
Chapter 10
8
Polystyrene
• Change a –H to benzene ring
• Widely used
– Disposable cups
– Insulation
Chapter 10
9
Vinyl Polymers
• Change a –H to –Cl
• Tough thermoplastic
– Polyvinyl chloride (PVC)
Chapter 10
10
Teflon
• Change all –H to –F
– C–F very strong. Resists heat and
chemicals
– Makes very unreactive polymer
Chapter 10
11
Other Polymers
Chapter 10
12
Practice Problems
Chapter 10
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
CH2
HC
C
CH3
H2C
Chapter 10
14
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
15
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
16
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
17
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
18
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
19
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
20
Chapter 10
21
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
22
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
23
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
Chapter 10
24
Recycling
• Collect, sort, chop, melt, and then
remold plastic
• Requires strong community cooperation
Chapter 10
25
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
Chapter 10
26
End of Chapter 10
Chapter 10
27