11a. More on POLYMERS - synthetic macromolecules

• Most polymers (plastics) are made from alkene compounds containing the -C=C- bond by addition polymerisation.
• The general reaction is small monomer molecule ==> long polymer molecule as the small molecules link together to form a long chain.
• Poly(chloroethene) is made from chloroethene (old name 'vinyl chloride), CH₂=CHCl but the polymer is generally called polyvinylchloride, PVC.
• The general equation and the formation of poly(ethene) and poly(propene) (^*old/wrong names: polythene, polyethylene AND polypropylene).
• The formation of PVC is shown below.

• Above is a 'picture' of a section of a very long chain poly(chloroethene) polymer molecule (PVC), essentially consisting of hundreds or thousands of -CH₂-CHCl- chloroethene units all joined together.

• The above diagram is that of a 'ball and stick' type of model and although it looks straight, in reality, the long molecule will be all twisted-jumbled up like in the diagram on the right.

• The chlorine atoms are shown as a regular arrangement, but they will be more randomly distributed down the ...-C-C-C-... chain depending on which way round the chloroethene molecule added.

• Polymers (plastics) consist of a tangled mass of very long molecules in which the atoms are joined by strong covalent bonds to form long chains, but there are much weaker intermolecular forces holding the material together.
• COMPARISON OF THERMOPLASTICS and THERMOSETS
• In thermosoftening plastics like poly(ethene), poly(propene) or poly(chloroethene) PVC, because the inter-molecular attractive forces between the chains are weak, the plastic softens when heated and hardens again when cooled. It also means the polymer molecules can slide over each other. This means they can be easily stretched or moulded into any desired shape.
  • They are examples of thermoplastics (thermosoftening plastics), because they can be heated to make them softer - more plastic, reshape it e.g. in an injection mould system, and on cooling the plastic object retains its new shape - bottle, bowl, toy etc.
  • However it is possible to manufacture and process plastics in which the polymer chains are made to line up. This greatly increases the intermolecular forces between the 'aligned' polymer molecules and strong fibre strands of the plastic can be made.
  • Examples: The addition polymer poly(propene) and the condensation polymers nylon and Terylene
• When a thermosetting plastic is first heated covalent bonds are formed between adjacent chains of the polymers. These strong covalent cross-linkages give the material a high melting point and greatly increased strength and rigidity. They also prevent thermosetting plastics from being softened with heat and therefore from being stretched or re-shaped. However it does make a much stronger material and not as flammable. On heating strongly they do NOT melt, but tend to char, gradually giving off gases.

• 

• Some plastic polymers like nylon and terylene (see below) can be drawn out into thin strong fibres.

• Melamine (used in furniture) and many glues are examples of thermosetting polymers.
• See also ....
  • Problems with using plastics are in section 7. Polymers-plastics page.
  • Some basic notes on polymers and plastics in the Section 7 Oil Products Polymer Notes e.g. the formation of poly(ethene), polypropene and poly(chloroethene) PVC.
  • Some important structure, strength and 1D, 2D 3D dimension structural concepts) in the Chemical Bonding notes.

11b. More on Other Synthetic Polymers - macromolecules

Condensation polymerisation involves linking lots of small monomer molecules together by eliminating a small molecule. This is often water from two different monomers, a H from one monomer, and an OH from the other, the 'spare bonds' then link up to form the polymer chain.

• Nylon (a polyamide) is formed by condensation polymerisation, the structure of nylon represented below where the rectangles represent the rest of the carbon chains in each unit. (more representations on the Organic Nitrogen Compounds advanced structure page.
• (3 units etc.)
• This is the same linkage (-CO-NH-) that is found in linked amino acids in naturally occurring macromolecules called proteins, where it is called the 'peptide' linkage.
  • Nylon-6,6
• Terylene (a polyester) is formed by condensation polymerisation and the structure of Terylene represented as
•    (3 units etc.)
• This is the same kind of 'ester linkage' (-COOC-) found in fats which are combination of long chain fatty carboxylic acids and glycerol (alcohol with 3  -OH groups, a 'triol').
• Terylene (polyester) and nylon are good for making 'artificial' or 'man-made' fibres used in the clothing and rope industries.
  • In the manufacturing process the polymer chains are made to line up.
  • This greatly increases the intermolecular forces between the 'aligned' polymer molecules and strong fibre strands of the plastic can be made.
• Some important structure, strength and 1D to 3D dimension concepts are in the Chemical Bonding notes.
• -

Multiple Choice Quizzes and Worksheets

KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products (easier-foundation-level)

KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products (harder-higher-level)

KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry

and 3 linked easy Oil Products gap-fill quiz worksheets

ALSO gap-fill ('word-fill') exercises originally written for ...

... AQA GCSE Science Useful products from crude oil AND Oil, Hydrocarbons & Cracking etc.

... OCR 21st C GCSE Science Worksheet gap-fill C1.1c Air pollutants etc ...

... Edexcel 360 GCSE Science Crude Oil and its Fractional distillation etc ...

... each set are interlinked, so clicking on one of the above leads to a sequence of several quizzes

Advanced Level Organic Chemistry revision notes

Revise KS4 Science GCSE/IGCSE/O level Chemistry Revision-Information Study Notes for revising for AQA GCSE Science, Edexcel 360Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science WJEC/CBAC GCSE science-chemistry CCEA/CEA GCSE science-chemistry (and courses equal to US grades 8, 9, 10)