polymers chapter 21. introduction o what is a polymer? o a very large molecule made up of identical...

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Polymers Chapter 21

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PolymersChapter 21

IntroductionO What is a polymer? O A very large molecule made up of

identical smaller units (minimum 50), which repeat.

O Monomer? The small identical units.O Plastic: polymers of organic

moleculesO Examples of plastics: PVC, PET,

Polythene, polyester

Addition Polymerisation

O Alkenes are able to react together and form polymers: Why?

O C=C double bonds: these can break open and bond together.

O Where do we get these alkenes from?O Cracking of large molecules in crude oil. O Heat, high pressure, and an initiator are

needed. O Initiator is not a catalyst. O The initiator is not left unchanged at the

end of the reaction, but gets bonded to the ends of the molecule.

Poly(e)theneO Polymer of etheneO Chain varies from 4000-40000 C atoms

in length

Uses of polytheneO Low-density (LDPE): ethane

compressed, 200C, with O2, molecular mass: 50,000-300,000. Thin, flexible, not strong: plastic bags.

O High density (HDPE): Zieger catalyst (titanium), molecular mass 50,000- 3 million. Stronger, more rigid: plastic milk bottles.

PolypropeneO Polymer of propene: addition

polymerisationO Stronger than polytheneO Ropes and crates

PVCO Polymer of chloroethene

(old name vinyl chloride)O Strong, rigidO Electrical insulation, drainpipes,

plastic sheets, clothing (with added chemicals to make it more flexible)

PETPolyethylene terephthalate

Condensation Polymerization

O Polymers can also be made by joining two different types of molecules together.

O They react together and a small molecule, usually water, is lost (hence the name).

O What examples do you already know?

Making nylon