Chemistry: Macromolecules

Chemistry: Macromolecules

1. 1. Introduction

   • Very big molecules, containing thousands of atoms
     • eg. haemoglobin -> each molecule abt 9000 atoms & relative molecular mass abt 64,000
     • Polymers: made up of many small molecules called monomers (50 to 50,000) joined together
       • Polymerisation: process of joining these small molecules tgt though colvalent bonds to form macromolcules
     • No sharp melting point, soften over range of temperature
     • Naturally occurring: starch, cellulose, latex, fats, proteins
     • Synthetic (plastics): polyethene, polystyrene & polyvinylchloride (PVC)

2. 2. Synthetic Macromolecules (Polymers)

   • 2.1 Addition Polymerisation
     • Linking together of unsaturated monomers to form polymers
     • a. formation of ethene
     • b. properties of polyethene
       • Resistant to chemicals & does no dissolve in water at room temp
     • c. uses
       • Typical plastics used for packaging food, electronics etcs
   • 2.2 Condensation Polymerisation
     • Linking together of monomers with the elimination of a simple molecule like water or hydrogen chloride
     • 2.2.1 Terylene
       • A synthetic fiber made from reaction b/n a dicarboxylic acid (contains 2 -COOH groups) & a diol (contains 2 -OH groups)
       • form ester linkage w/ the elimination of a water molecule
         • hence, Terylene is a type of polyester bcuz many ester linkages in each molecule
       • a. formation of Terylene
       • b. properties of Terylene
         • Resistant to attacks by chemicals or fungus & does not crumple easily
       • c. uses of Terylene
         • To make fabrics for manufacture of clothing
         • Not as absorbent as cotton, thus cool to wear
           • Often combined w/ cotton to produce polyester - cotton fabrics
     • 2.2.2 Nylon
       • A synthetic fiber (first made in New York & London) made from reaction b/n a diamine (contain 2 -NH2 groups) & a dicarboxylic acid (contains 2 -COOH groups)
       • form amide linkage w/ the elimination of water molecule
         • Hence, nylon is a type of polyamide bcuz many amide linkages in each molecules
       • a. formation of nylon
       • b. properties of nylon
         • Strong & resistant to attack by fungus + bacteria
       • c. uses of nylon
         • To make fabrics & garments e.g. socks & stockings
         • To make strong ropes & lightweight machine parts

3. 3. Pollution problems caused by the disposal of non-biodegradable plastics

   • Plastics used to replace natural materials bcuz:
     • Relatively cheaper & could be molded easily into diff shapes
     • Lighter, tougher & waterproof
     • Durable -> resistant to decay, rusting & chemical attacks
   • However, most common plastics non-biodegradable -> cannot be decomposed by bacteria in soil
     • bury plastic waster in landfill but cannot decompose -> land pollution
     • Most plastics gotten rid of by burning (incineration) -> produce poisonous gases -> air pollution
       • eg. PVC produces hydrogen chloride gas on burning

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