Chapter 10

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 CH War II 2 =CH 2 – Invented shortly before World • Has two forms – High-density polyethylene (HDPE) – Low-density polyethylene (LDPE) Chapter 10 7

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 8

Polypropylene

• Change a –H to –CH 3 • Harder and has higher melting point than polyethylene Chapter 10 9

Polystyrene

• Change a –H to benzene ring • Widely used – Disposable cups – Insulation Chapter 10 10

Vinyl Polymers

• Change a –H to –Cl • Tough thermoplastic – Polyvinyl chloride (PVC) Chapter 10 11

Teflon

• Change all –H to –F – C–F very strong. Resists heat and chemicals – Makes very unreactive polymer Chapter 10 12

Other Polymers

Chapter 10 13

Practice Problems

Chapter 10 14

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 H 2 C Chapter 10 CH 3 15

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 16

Synthetic Rubber

• Use butadiene – CH 2 =CH-CH=CH 2 • Polychloroprene: substitute –Cl for a –H • Change the properties for other uses – Tend to be resistant to chemicals Chapter 10 17

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 18

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 19

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 20

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 21

Chapter 10 22

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 23

• Glass transition temperature,

T

g – Above

T

g , polymer is rubbery and tough – Below

T

g , polymer hard, stiff, and brittle • Determine where polymer will be used • What type of

T

g do you want your plastic coffee cup to be?

Chapter 10 24

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 25

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 26

Recycling

• Collect, sort, chop, melt, and then remold plastic • Requires strong community cooperation Chapter 10 27

Plasticizers

• Make plastic more flexible and less brittle – Lower

T

g – Tend to be lost as plastic ages • Most common plasticizers today based on phthalic acid O C OH OH C O Chapter 10 28