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

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 4

Some Naturally Occurring Polymers

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 10

Polystyrene

• Change a –H to benzene ring

• Widely used – Disposable cups– Insulation

Chapter 10 11

Vinyl Polymers

• Change a –H to –Cl

• Tough thermoplastic– Polyvinyl chloride (PVC)

Chapter 10 12

Teflon

• Change all –H to –F– C–F very strong. Resists heat and

chemicals– Makes very unreactive polymer

Chapter 10 13

Other Polymers

Chapter 10 14

Practice Problems

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 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

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

Chapter 10 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

C

OH

O

OH

C

O