Condensation Polymers

Condensation reactions of polymers

If a polymer is a compound made from several repeating units called monomers, then a condensation polymer is just a polymer that is formed using a condensation reaction. A condensation reaction is a chemical reaction that joins two molecules by removing a smaller molecule, commonly water. This small molecule is known as a condensate.

Condensation polymers are made from smaller monomers. These monomers can be exactly the same molecule or totally different. However, each monomer needs two functional groups, one at each end. If the monomer has two different functional groups, say both a hydroxyl group and a carboxyl group, then great - it can form a condensation polymer by joining up with other molecules of itself. But if it contains two of the same functional group, you'll need another type of monomer as well.

Types of condensation polymers

There are a few important types of condensation polymers.

• Polyamides
• Polyesters
• Polypeptides

These condensation polymers are created using different monomers, getting their names from the type of link formed during polymerisation. For example, polyamides have amide links, polyesters have ester links, and polypeptides have peptide links.

We'll focus on all three of these polymers here.

Polyamides

Here's a molecule. It has the amide functional group, -NHCO-. This consists of an amine group bonded to a carbonyl group - or in other words, a nitrogen atom bonded to a C=O.

Amide functional group. Anna Brewer, StudySmarter Original

Polyamides are long polymers made from lots of smaller monomers joined together by amide groups. We call these amide linkages. Like all condensation polymers, they're made in a condensation reaction; in this case, the condensate released is water.

Polyamides can be made from a variety of different reactants.

• A diamine and a dicarboxylic acid.
• A diamine and a dioyl chloride.
• Two aminocarboxylic acids.
• Two amino acids.

Here's an example of making a polyamide from a diamine and a dicarboxylic acid. A hydroxyl (-OH) group from the dicarboxylic acid reacts with a hydrogen atom from one of the diamine's amine groups, forming water. This results in an amide linkage between the diamine and the dicarboxylic acid. Because both molecules have two functional groups, one at each end, the process happens again. This creates a long polyamide polymer chain.

The polymerisation reaction between a diamine and a dicarboxylic acid creates a polyamide and water. Anna Brewer, StudySmarter Original

Polyesters

Let's look at another type of molecule. This one has an ester functional group, -COO-.

The ester functional group. Anna Brewer, StudySmarter Original

Polyesters are long polymers made from many smaller monomers in a condensation reaction, releasing water. This is very much like polyamides. But unlike polyamides, polyesters contain the ester linkage.

Polyesters can be made from a variety of different reactants:

• A diol and a dicarboxylic acid.
• A diol and a dioyl chloride.
• A hydroxycarboxylic acid.

Here's an example of making a polyester from a diol and a dicarboxylic acid. Similar to the reaction that makes a polyamide, a hydroxyl (-OH) group from the dicarboxylic acid reacts with a hydrogen atom from one of the diol's hydroxyl groups, forming water. This results in an ester linkage group between the dicarboxylic acid and the diol. Because both molecules have two functional groups, one at each end, the process happens again. This creates a long polyester polymer.

Polypeptides

Polypeptides are also a type of polyamide, containing the amide functional group. However, instead of needing two different monomers, they are made from just one type of monomer: an amino acid.

An amino acid. Anna Brewer, StudySmarter Original

Because amino acids contain both the amine functional group and the carboxyl functional group, they don't need a different type of monomer with which to react - they can react with each other. The amine group from one amino acid reacts with the carboxyl group of another, joining the two together using an amide linkage group. This is another example of a condensation reaction that releases water as a condensate. When just two amino acids join together, it forms a dipeptide, but the process repeats, forming a long polymer chain known as a polypeptide. Polypeptides are also called proteins.

The polymerisation reaction between two amino acids creates a polypeptide and water. Anna Brewer, StudySmarter Original

Condensation polymer examples

Let's move on to having a look at examples of condensation polymers. In particular, we'll focus on examples of polyamides and polyesters. These include:

• Nylon-6,6
• Kevlar
• Terylene

Nylon-6,6

Nylon-6,6 is an example of a polyamide. It is made in a condensation reaction between 1,6-diaminohexane and hexane-1,6-dicarboxylic acid. This releases water.

Producing nylon-6,6. Anna Brewer, StudySmarter Original

Nylon is used not only in various clothing and textiles, from carpets and jumpers to horse turnout rugs, but also in zip ties and hoses.

Kevlar

Kevlar is another example of a polyamide. It's made by reacting benzene-1,4-diamine with benzene-1,4-dicarboxylic acid in a condensation reaction, releasing water.

Making Kevlar. Anna Brewer, StudySmarter Original

Kevlar has an extremely high tensile strength to weight ratio, making it perfect for bulletproof vests and racing sails. It is also used in the science industry to separate vacuum-sealed containers from areas under normal atmospheric pressure.

Terylene

The final example of a polymer we'll look at today is Terylene. Terylene is a polyester, made from ethane-1,2,diol and benzene-1,4-dicarboxylic acid in a condensation reaction. Once again, this releases water as the condensate.

Making Terylene. Anna Brewer, StudySmarter Original

Terylene is commonly known as PET and is used for clothing, wet weather gear, food packaging, and microfibre towels.

Condensation polymers structure

In your exam, you need to know how to identify not only the condensation polymer made from two monomers, but also the monomers used to make a condensation polymer. Let's give this a go.

To find the condensation polymer from the monomer, we first need to identify the small molecule that is lost in the condensation reaction. Here, we are reacting a diol with a dicarboxylic acid, so the molecule released will be water. We then identify exactly which atoms are lost to make this small molecule. Here, we lose two hydrogen atoms and an oxygen atom. We then take these atoms away from monomers and join the monomers together, forming a polymer. Here, we make a polyester.

Alternatively, you could identify the parts of the monomers that form the ester linkage. When you join these together, you create the polymer.

Predicting the polymer from the monomers. Anna Brewer, StudySmarter Original

Let's now try the reverse: identifying the monomers that make up a condensation polymer.

Firstly, we can see that this polymer contains the amide functional group. It is therefore a polyamide. We know that polyamides can be made in different ways, but the question tells us that in this case, the monomers are a diamine and a dicarboxylic acid.

Remember how polyamides are formed when diamines and dicarboxylic acids react in a condensation reaction? The diamine loses a hydrogen atom and the dicarboxylic acid loses a hydroxyl group, -OH, which react together to form a water molecule. The diamine and the dicarboxylic acid then join using an amide linkage group.

To break a polyamide, we do the reverse - we add water. Adding water splits the polymer down the middle of the amide group, adding a hydrogen atom to the amine, and a hydroxyl group to the carboxylic acid. This leaves us with our monomers. In this case, we are left with 1,2-diaminoethane and benzene-1,4-dicarboxylic acid.

Predicting the monomers from the polymer. Anna Brewer, StudySmarter Original

Condensation polymers and intermolecular forces

We've learned about the bonding within long condensation polymer chains. For example, polyamides are joined using the amide linkage group, and polyesters are joined using the ester linkage group. But what about the bonding between condensation polymer chains?

Well, both the amide functional group and the ester functional group are polar. This means that both polyamides and polyesters experience permanent dipole-dipole forces between polymer chains. However, the amide functional group contains a nitrogen atom bonded to a hydrogen atom. This means that polyamides can also form hydrogen bonds. These intermolecular forces increase the strength of polyamides and polyesters.

Addition and Condensation Polymers

To finish, let's compare condensation polymers with addition polymers.

That's it!

By now, you should know what condensation polymers are, and how various examples are made. You should also be able to draw the condensation polymer formed from two given monomers, and deconstruct a polymer down into its monomers. Finally, you should have an understanding of the intermolecular forces between condensation polymer chains, and the differences between addition and condensation polymers.