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Initiation, propagation and termination

There are three stages in the process of addition polymerisation. Initiation refers to a chemical reaction that triggers off another reaction. In other words, initiation is the starting point of the polymerisation reaction. Chain propagation is the part where monomers are continually added to form a longer and longer polymer chain. During chain propagation, it is the reactive end groups of the polymer chain that react in each propagation step, to add a new monomer to the chain. Once a monomer has been added, the reactive part of the polymer is now in this last monomer unit so that propagation will continue. Termination refers to a chemical reaction that destroys the reactive part of the polymer chain so that propagation stops.

A polymerisation reaction takes place and the following polymer is formed:

Note: W, X, Y and Z could represent a number of different atoms or combinations of atoms e.g. H, F, Cl or CH 3 .

  1. Give the structural formula of the monomer of this polymer.
  2. To what group of organic compounds does this monomer belong?
  3. What type of polymerisation reaction has taken place to join these monomers to form the polymer?
  1. The monomer is:

  2. The monomer has a double bond between two carbon atoms. The monomer must be an alkene.

  3. In this example, unsaturated monomers combine to form a saturated polymer. No atoms are lost or gained for the bonds between monomers to form. They are simply added to each other. This is an addition reaction.

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Condensation polymerisation

In this type of reaction, two monomer molecules form a covalent bond and a small molecule such as water is lost in the bonding process. Nearly all biological reactions are of this type. Polyester and nylon are examples of polymers that form through condensation polymerisation.

  1. Polyester Polyesters are a group of polymers that contain the ester functional group in their main chain. Although there are many forms of polyesters, the term polyester usually refers to polyethylene terephthalate (PET). PET is made from ethylene glycol (an alcohol) and terephthalic acid (a carboxylic acid). In the reaction, a hydrogen atom is lost from the alcohol, and a hydroxyl group is lost from the carboxylic acid. Together these form one water molecule which is lost during condensation reactions. A new bond is formed between an oxygen and a carbon atom. This bond is called an ester linkage . The reaction is shown in [link] .
    An acid and an alcohol monomer react (a) to form a molecule of the polyester 'polyethylene terephthalate' (b).
    Polyesters have a number of characteristics which make them very useful. They are resistant to stretching and shrinking, they are easily washed and dry quickly, and they are resistant to mildew. It is for these reasons that polyesters are being used more and more in textiles . Polyesters are stretched out into fibres and can then be made into fabric and articles of clothing. In the home, polyesters are used to make clothing, carpets, curtains, sheets, pillows and upholstery.

    Interesting fact

    Polyester is not just a textile. Polyethylene terephthalate is in fact a plastic which can also be used to make plastic drink bottles. Many drink bottles are recycled by being reheated and turned into polyester fibres. This type of recycling helps to reduce disposal problems.
  2. Nylon Nylon was the first polymer to be commercially successful. Nylon replaced silk, and was used to make parachutes during World War 2. Nylon is very strong and resistant, and is used in fishing line, shoes, toothbrush bristles, guitar strings and machine parts to name just a few. Nylon is formed from the reaction of an amine (1,6-diaminohexane) and an acid monomer (adipic acid) ( [link] ). The bond that forms between the two monomers is called an amide linkage . An amide linkage forms between a nitrogen atom in the amine monomer and the carbonyl group in the carboxylic acid.
    An amine and an acid monomer (a) combine to form a section of a nylon polymer (b).

Questions & Answers

how do you see a product if it is exothermic
Entle Reply
When ∆H<0
Thuto
H<0
Dikeledi
does these circles shown show the observer ?
Amahle Reply
can you mix kc nd pressure
Khanyisile Reply
equation for dissociation
Amanda Reply
under which topic
Phila
acids and bases
Amanda
Newton's law
Anna
How does a catalyst affect the rate of chemical reaction
Rebone Reply
it speeds up the reaction without being by the reaction. in other words it increases the Reaction rate by lowering the activation energy of a reaction
Keabetsoe
hey
Siphokazi
ey
Keabetsoe
🙄
Holy
it only speed up the reaction not to affect the reaction
John
what is a compound?
Sithembiso Reply
define Doppler effect
Emihle Reply
It is the change in frequency of a wave in relation to an observer who is moving relative to the wave source.
Junior
Doppler effect is the change in frequency or pitch detected by a listener because the velocity of the sound source is different from that of a listener relative to the medium of sound propagation
John
explain how color is an unreliable clue to.the identify minerals
Camille Reply
Hi I want to know where the topic for electric circuits are?
Zahra Reply
hello.. How to deal with Reactions rate?. i dont Understand them
Simphiwe Reply
Firstly you must know how energy changes during chemical reactions...secondly the collision theory.... Rate and extent of reactions.... And factors that affect the rate of chemical reactions... If u capture all the topic then this chapter will be easy for you the is no way you can fail it...
Pearly
thank you
Petty
Heii.. I'm struggling with chemical equilibrium.
Ronny
how do I attempt chemical equilibrium?
Ronny
doppler effect question
Mabikinyane Reply
How do I differentiate from the formula of a listener who is moving away and who is moving towards the source
Njabulo
if the its away you will subtract on the numerator and add in the denominator but if its towards its the opposite
Ashley
how cn I calculate sound of a source if it's unkown
Simphiwe Reply
Use what you were given. What were you given?
Bandile
where can I find acids and bases
muravha Reply
how to calculate avarage power?
Bongani Reply
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Soluiswayi Reply
Good day Sir
noma
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Aobakwe
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clifort
How are you
Aobakwe

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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