Chapter 26 : Macromolecules

1. Chapter 26 : Macromolecules • What are macromolecules? • How are macromolecules formed? • Types of macromolecules • Synthetic and Natural Polymers • Uses of Polymers

2. Macromolecules What are they? A very large (giant) covalent molecule made up of large number of small identical molecules. Have veryhigh relative molecular mass, Mr e.g. haemoglobin, DNA, fat, diamond Compared to CCl4, H2O – small molecules with finite number of atoms in each molecule

3. Haemoglobin molecule – iron protein compound found in red blood cells A natural macromolecule made up of 9000 atoms. Mr ~ 68 000

4. Macromolecules When large number of small molecules link together to form a macromolecule, the process is called polymerisation. Macromolecule formed is called a polymer; small molecules are called monomers

5. Macromolecules polymerisation General condition for polymerisation: High temperature and high pressure and use of a catalyst/an initiator

6. Polymers Synthetic Polymers Natural Polymers fats proteins Carbo- hydrate Condensation Polymers Addition Polymers Egs poly(ethene) PVC Polyester Eg Terylene Polyamide Eg nylon

7. Synthetic Polymer Natural polymer Synthetic / Natural Polymers Made from petroleum products Human hair magnified 400 times Comes mainly from plants/animals e.g. wool, cotton, silk

8. Addition Polymerisation Addition Polymerisation Linkage of many small unsaturated molecules of the same kind, without losing any molecules or atoms.

9. Example 1 : Addition Polymer • Poly(ethene) or commonly called polythene • Monomer : ethene (C2H4) • Structure of monomer

10. Animation - Formation of poly(ethene)

11. Addition Polymerisation Monomer with a C=C bond ..+ +++ +.. Poly(ethene)

12. Poly(ethene) or polythene Repeat unit Formula of polymer n is a very large number (n ~ 500 to 20,000)

13. Polymer Uses Properties Alkene • Plastic film for • wrapping • plastic bags, • plastic bottles, • buckets • Resistant to • attackby acids • in food • strong and • flexible Examples of Addition Polymers view

14. Examples of Addition Polymers Polymer Uses Properties Alkene • Bottles for oils • and chemicals • For ropes, • carpets, • car bumpers, • furniture, • artificial turf • Not attacked • by chemical • solvents • tough and • hard, can be • moulded

15. Examples of Addition Polymers Polymer Uses Properties Alkene • water pipes • waterproof • plastic • sheeting • insulation • for electric • cables and • wires • strong and • flexible • waterproof, • weather • resistant • does not • conduct • electricity view

16. Examples of Addition Polymers Polymer Uses Properties Alkene • coat non-stick • pots and pans • containers for • chemical in • factories • heat resistant • repels water, • few substance • can stick to its • surface • acid resistant view

17. Examples of Addition Polymers Polymer Uses Properties Alkene • for disposable • cups and food • containers • Packaging • fragile goods • e.g. cameras • hard but • brittle • low density, • excellent • thermal • insulator view

18. Examples of Addition Polymers Polymer Uses Properties Alkene • make contact • lenes, • sunglasses, • vehicle • windshields, • “perspex” • windows panes • transparent, • less easily • shattered than • glass

19. Copolymerisation • obtained when 2 or more different monomers polymerize together. • The polymer structure can be • random or alternating. • Random polymer: -[A-B-B-A-A-A-A-B-] • Alternating polymer: -[A-B-A-B-A-B-]

20. where and contains carbon and hydrogen atoms (see examples) Example 1 : Nylon – a condensation polymer • Made by condensation polymerisation involving two types of monomers • Simplified structure of monomers dicarboxylic acid diamine

21. Animation (Formation of Nylon)

22. + n H-O-H Condensation Polymerisation + + + + +

23. Example 1 : Nylon Simplified structure Small molecules of water are eliminated during the process The units of nylon are joined together by amide (or peptide) linkages Nylon is also known as a polyamide Repeating unit

24. where and contains carbon and hydrogen atoms (see examples) Example 2 : Terylene – a condensation polymer • Made by condensation polymerisation involving two types of monomers • Simplified structure of monomers dicarboxylic acid diol

25. Example 2 : Terylene Simplified structure Small molecules of water are eliminated during the process The units of terylene are joined together by ester linkages Terylene is also known as a polyester Repeating unit

26. Uses of condensation polymers Nylon - view

27. Uses of condensation polymers Terylene - view

28. Pollution caused by using non-biodegradable plastics A plastic is a polymerised organic substance, a solid of high molar mass, which at some time in its manufacture can be shaped by flow. All man-made polymers are plastics. The uses of plastic have grown enormously due to their special characteristics: • Tough, waterproof and have low density • Resistant to decay, rusting and chemical attack • Relatively cheap and can easily be moulded into various shapes. • Do not conduct electricity • Can be made very strong • Can be coloured by adding pigments

29. Disadvantages of Using Plastics • Problems: • (1) Pose a serious fire hazard (Some plastics catch fire very easily. Molten plastic can inflict severe burns) and • When plastic burn, they can produce toxic gases such as • carbon monoxide (due to incomplete combustion). • Plastics such as PVC produce hydrogen chloride gas (air pollutant and may cause acid rain.) when burnt. • (3) Plastics are non-biodegradable. They cannot be broken down into simple substances by bacteria in the soil. Thus, discarded plastic objects accumulate, pollute the environment and cause long-term land pollution. (see picture)