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