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From plastic bags and proteins to clothing and cellulose, our world is full of polymers. They are formed through polymerisation.
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Sign up for freeHow many products are formed in addition polymerisation?
How many different types of functional groups are required for addition polymerisation?
How many products are formed in condensation polymerisation?
How many different types of functional groups are required for condensation polymerisation?
What sort of polymerisation does propene undergo?
How many products are formed in addition polymerisation?
How many different types of functional groups are required for addition polymerisation?
How many products are formed in condensation polymerisation?
How many different types of functional groups are required for condensation polymerisation?
What sort of polymerisation does propene undergo?
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Team Polymerisation Reactions Teachers
A polymer is a large molecule made up of repeating units called monomers.
Examples of polymers include proteins, DNA, and plastics such as polyvinyl chloride (PVC) and polystyrene. We will focus here on these plastics, including polyamides, polyesters, and polymers made from alkenes, and the reactions that form them. These reactions are collectively known as polymerisation reactions.
Check out Proteins Biochemistry and DNA structure for a look at protein and DNA polymers. If you want a more biology-focused view of these structures, you can find out more in the articles Proteins and DNA.
Polymers are formed in two different types of reactions. These depend on the functional groups of the monomer or monomers used:
Let's explore these types more closely.
Addition polymerisation is the joining together of monomers with the C=C double bond to form a large molecule known as a polymer. This process doesn't produce any other by-products.
Alkenes can undergo addition polymerisation to form long hydrocarbon chain polymers known as polyalkenes. The monomers used can all be the same alkene, or of multiple different types. The C=C double bond in each monomer opens up and binds to the adjacent monomer to form a C-C backbone. This is shown below with the example of ethene:
Addition polymerisation with ethene. StudySmarter Originals
Addition polymerisation can be represented by the following equation. We use -R to represent any varying alkyl or aryl group. The letter 'n' represents the number of alkene monomers used, which tends to be very large:
Ethene polymerises to form poly(ethene), also known as polythene. StudySmarter Originals
This is called a polymerisation equation.
Addition polymers are named using the prefix poly- and the name of their alkene monomer, in brackets. For example, chloroethene polymerises to form poly(chloroethene). However, many of these polymers have different trade names, and poly(chloroethene) is also known as polyvinyl chloride, or PVC.
When asked to find the repeating unit of a given addition polymer, you should remember that each monomer is based around a C=C double bond. Therefore, every pair of carbons in the C-C backbone of the polymer will belong to a different monomer. The monomers can also be worked by identifying the polymer’s repeating pattern, such as in the example below:
From polymer to monomer. StudySmarter Originals
The table below shows some examples of monomers and their polymers.
A table showing different monomers and their polymers. StudySmarter Originals
Free radical polymerisation is a type of addition polymerisation in which a free radical joins non-radical monomers in a chain, forming a polymer.
A free radical is a species with an unpaired outer shell electron. Non radicals are therefore species without an unpaired outer shell electron.
The radical is initiated by heating or radiation. This destroys a bond homolytically, meaning one electron goes to each of the two new molecules, creating two free radicals. The radical then adds to a monomer, forming a larger radical. This is shown by the equation below, where R is a free radical and M is a monomer:
The larger radical then adds to another monomer:
The process continues until termination. Termination involves two radicals reacting together to form a stable compound:
Free-radical polymerisation can be represented by the following general equation:
Condensation polymerisation is a type of condensation reaction in which monomers join together to form a large polymer, releasing a small molecule in the process. This small molecule is often called the condensate.
Condensation polymers are based around two different functional groups. These could be from two unique monomers, or from one monomer containing two different functional groups. In order for the monomers to form a continuous chain, there must be two functional groups on each monomer.
Examples of condensation polymers include:
Polyamides are formed in the reaction between an amine and a carboxylic acid. As each monomer must have two functional groups in order to form a polymer, the monomers are often diaminoalkanes and dicarboxylic acids.
A dicarboxylic acid, left, and a diamine, right. StudySmarter Originals
The condensate released is water, resulting in the amide functional group -NCO- repeated throughout the molecule. This can be represented by the following equation, in which the molecules lost are shown in red.
A condensation reaction between a diamine and a dicarboxylic acid forms a polyamide. StudySmarter Originals
For example, Nylon-6,6 is made from 1,6-diaminohexane and hexane-1,6-dicarboxylic acid:
Nylon-6,6. StudySmarter Originals
Polyesters are formed from alcohols and carboxylic acids. Often the monomers are diols and dicarboxylic acids.
A diol, left, and a dicarboxylic acid, right. StudySmarter Originals
Again, the condensate is water, resulting in the ester functional group -COO- repeated throughout the molecule. The general equation is shown below:
A condensation reaction between a diol and a dicarboxylic acid forms a polyester. StudySmarter Originals
For more information on alcohols, amines, or carboxylic acids, see Alcohols, Amines, and Carboxylic Acids and Esters respectively.
To identify the monomers used from a polymer chain, it can help to locate the repeating -COO- or -NCO- functional group. You can then divide the molecule into its repeating units. For example, this polymer is made up of 1,2-ethanediol and butane-1,4-dioic acid:
From polymer to monomer. Can you spot the repeating -COO- group? StudySmarter Originals
Sometimes, only one monomer is required for a condensation reaction. This occurs if the molecule contains two different suitable functional groups. For example, 2-hydroxyethanoic acid can form a polymer with the following repeated unit:
Sometimes, only one monomer is required for a condensation reaction. This occurs if the molecule contains two different suitable functional groups. For example, 2-hydroxyethanoic acid can form a polymer with the following repeated unit:
Because this species contains both the -OH and -COOH functional groups, it doesn't require another type of molecule in order to form a polymer. StudySmarter Originals
The following table shows the similarities and differences between addition and condensation polymerisation.
A table comparing addition and condensation polymerisation. StudySmarter Originals
If you want to learn more about polymers, visit the article with the same name (Polymers) for further reading. You can also check out Condensation Polymers to find out more about condensation polymers in particular.
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What is polymerisation?
Polymerisation is a chemical reaction in which small molecules called monomers join together to make a large chain molecule called a polymer.
Why is polymerisation a type of addition reaction?
Not all types of polymerisation are addition reactions. However, polymerisation reactions involving alkenes are addition reactions, because they combine two smaller molecules to make a larger one.
What are the two types of polymerisation reaction?
The two types of polymerisation reaction are addition polymerisation and condensation polymerisation.
What happens in a polymerisation reaction?
In a polymerisation reaction, small molecules called monomers join together to form a polymer. In addition polymerisation, they do this by adding across a C=C double bond. In condensation polymerisation, they do this by reacting together and releasing a small molecule known as a condensate. Often this molecule is water.
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