Post on 28-Dec-2015
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
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 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 12
Teflon
• Change all –H to –F– C–F very strong. Resists heat and
chemicals– Makes very unreactive polymer
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 IICH2
CHC
H2C CH3
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 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