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

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

Some Naturally Occurring Polymers Chapter 10

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

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

Polyethylene Cheapest and simplest synthetic polymer Has two forms Made from CH2=CH2 Invented shortly before World War II Has two forms High-density polyethylene (HDPE) Low-density polyethylene (LDPE) Chapter 10

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

Polypropylene Change a –H to –CH3 Harder and has higher melting point than polyethylene Chapter 10

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

Vinyl Polymers Change a –H to –Cl Tough thermoplastic Polyvinyl chloride (PVC) Chapter 10

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

Other Polymers Chapter 10

Practice Problems Chapter 10

Rubber Pre–World War II Made of isoprene 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 Chapter 10

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

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

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

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

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

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

Chapter 10

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

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

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

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

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

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 Chapter 10