ChemistryChapter 12: Polymers
12.1.2 Condensation Polymers
**What they are:** - Condensation polymers are formed in a condensation reaction
Explanation level
What they are:
- Condensation polymers are formed in a condensation reaction where each time a bond is formed between two monomers, a small molecule (often water) is released.
- If one monomer contains a -OH group and the other -H, then they can be joined by eliminating a molecule of water.
- This reaction is called a condensation reaction.
- This type of polymerisation process is called condensation polymerisation.
- Condensation polymers are usually polyamides or polyesters formed by the reaction of functional groups (e.g., carboxyl and amino in polyamides or carboxyl and hydroxyl group in polyesters) with the removal of a small molecule such as water.
Repeating units:
- In condensation polymers, the repeating unit usually consists of two different types of monomers, each of which forms the polymer backbone with functional groups that react to form the polymer and release small molecules.
Example: Polyesters (PET)
- Polyesters such as polyethylene terephthalate (PET) are formed from terephthalic acid (HOOC-C6H4-COOH) and ethylene glycol (HO-CH2-CH2-OH).
- Monomers: Terephthalic acid and ethylene glycol (a diol)
- Repeating unit: -OC - C6H4 - COO - CH2 - CH2 - O-
- Released molecule: Water (H2O)
Example: Polyamides (Nylon-6,6)
- Polyamides such as nylon-6,6 are formed from hexamethylenediamine (H2N - (CH2)6 - NH2) and adipic acid (HOOC - (CH2)4 - COOH).
- Monomers: Hexamethylenediamine and adipic acid
- Repeating unit: -NH - (CH2)6 - NH - CO - (CH2)4 - CO-
- Released molecule: Water (H2O)
Key point: Condensation polymers are formed in a condensation reaction where a small molecule (often water) is released. They are usually polyamides or polyesters.
Summary Table
| Feature | Addition Polymers | Condensation Polymers |
|---|---|---|
| Formation | Adding monomer units without losing small molecules | Condensation reaction with release of small molecules |
| Monomers | Usually contain double or triple bonds | Contain functional groups (e.g., -OH, -COOH, -NH₂) |
| Repeating unit | Same as monomer, but with single bonds | Consists of two different types of monomers |
| Examples | Polyethylene, Polypropylene, PVC | Polyesters (PET), Polyamides (Nylon-6,6) |
| Released molecule | None | Water (often) |
Intermediate Level
Polymers:
- Large molecules built from many smaller repeating units called monomers.
- Monomers bond covalently to form long chains.
- Polymerisation = joining up of many monomers to form a big molecule.
Types of polymers:
| Feature | Addition Polymers | Condensation Polymers |
|---|---|---|
| Formation | Adding monomer units without losing small molecules | Condensation reaction with release of small molecules |
| Monomers | Usually contain double or triple bonds | Contain functional groups |
| Repeating unit | Same as monomer, but with single bonds | Consists of two different types of monomers |
| Examples | Polyethylene, Polypropylene, PVC | Polyesters (PET), Polyamides (Nylon-6,6) |
| Released molecule | None | Water (often) |
Key point: Polymers are classified into addition and condensation polymers based on their synthesis.
Solved Example
Example: Identify the Monomer and Repeating Unit of Polyethylene
Question: Identify the monomer and repeating unit of polyethylene.
Solution:
Monomer: CH2 = CH2 (ethene)
Repeating unit: -CH2 - CH2 -
Final Answer: Monomer: CH2 = CH2; Repeating unit: -CH2 - CH2 -
Example: Identify the Monomers of Nylon-6,6
Question: Identify the monomers of nylon-6,6.
Solution:
Monomers: Hexamethylenediamine (H2N - (CH2)6 - NH2) and adipic acid (HOOC - (CH2)4 - COOH)
Released molecule: Water (H2O)
Final Answer: Monomers: Hexamethylenediamine and adipic acid.
Concept Assessment Exercise 12.1
1. What type of bond is involved in the formation of addition polymers?
Answer: Covalent bonds (the double bond opens and forms single bonds).
2. What is released during the formation of addition and condensation polymers?
Answer: Addition polymers: nothing is released; Condensation polymers: a small molecule (often water) is released.
3. Give an example of a condensation polymer.
Answer: Polyethylene terephthalate (PET) or Nylon-6,6.
4. How do these building blocks come together to form polymers?
Answer: Monomers join together through covalent bonds. In addition polymerisation, the double bond opens and monomers add together. In condensation polymerisation, functional groups react and a small molecule (like water) is eliminated.
Important Points
- - Polymers = large molecules built from many smaller repeating units called monomers.
- - Monomers = small molecules that bond together to form polymers.
- - Polymerisation = joining up of many monomers to form a big molecule.
- - Monomers bond covalently to form long chains.
- - Polymers are classified into two categories:
- 1. Addition polymers — formed by adding monomer units without losing small molecules (e.g., polyethylene, polypropylene, PVC).
- 2. Condensation polymers — formed by condensation reactions with the release of a small molecule (often water) (e.g., PET, nylon-6,6).
- - Addition polymers: Monomers usually contain double or triple bonds.
- - Condensation polymers: Monomers contain functional groups (e.g., -OH, -COOH, -NH₂).
- - Repeating unit: For addition polymers, the repeating unit is the same as the monomer but with single bonds. For condensation polymers, the repeating unit consists of two different types of monomers.
- - Examples:
- - Polyethylene: n\ CH2=CH2 → (-CH2-CH2-)n
- - Polypropylene: n\ CH2=CH-CH3 → (-CH2-CH(CH3)-)n
- - PVC: n\ CH2=CHCl → (-CH2-CHCl-)n
- - PET: Terephthalic acid + ethylene glycol → PET + water
- - Nylon-6,6: Hexamethylenediamine + adipic acid → nylon-6,6 + water
Remember
- - Polymers = large molecules from many monomers.
- - Polymerisation = joining of monomers.
- - Two types: addition and condensation.
- - Addition polymers: no small molecule released; monomers have double/triple bonds.
- - Condensation polymers: small molecule (often water) released; monomers have functional groups.
- - Examples:
- - Addition: Polyethylene, Polypropylene, PVC.
- - Condensation: PET, Nylon-6,6.
- - Repeating unit: addition = same as monomer with single bonds; condensation = two different monomers.
- - Polyesters = ester linkages.
- - Polyamides = amide linkages.
Common Mistakes
| Mistake | Correction |
|---|---|
| Thinking polymers are small molecules | Polymers are large molecules built from many monomers |
| Confusing addition and condensation polymers | Addition: no small molecule released; Condensation: small molecule (often water) released |
| Forgetting that monomers bond covalently | Monomers bond covalently to form long chains |
| Thinking all polymers are plastics | Polymers can be plastics, fibres, or other materials |
| Confusing the repeating unit with the monomer | For addition polymers, the repeating unit is similar to the monomer but with single bonds |
| Forgetting that condensation polymers release a small molecule | Condensation polymers release a small molecule (often water) |
| Thinking polyesters and polyamides are the same | Polyesters have ester linkages; polyamides have amide linkages |
Quick Revision
Polymers:
Polymers are large molecules built from many smaller repeating units called monomers. These monomers bond covalently to form long chains giving polymers their unique properties. Polymerisation is the joining up of many monomers to form a big molecule. Polymers can be classified into two categories based on their synthesis: addition polymers and condensation polymers.
12.1.1 Addition polymers:
Addition polymers are formed by adding monomer units without losing the small molecules. Monomers usually contain double or triple bonds that open and combine to form a polymer. The number of carbon atoms in these chains can vary from 4000 to 40,000. For example; Ethene is the smallest hydrocarbon containing a carbon-carbon double bond. Ethene molecules can join together to produce very long chains. Part of the double bond is broken, and the electrons in it are used to join neighbouring molecules. This process is called addition polymerisation.
At high temperatures and high pressures, the monomer ethene joins up to give a polymer called polyethylene or polyethene.
- n\ CH2 = CH2 → (-CH2 - CH2 -)n
Repeating units: For a polymer, a repeating unit is the same as a monomer, except that the double bond is replaced by a single bond after polymerization.
Repeating unit: -CH2 - CH2 -
Polyethylene (PE) consists of ethylene monomer (CH2 = CH2)
Monomer: CH2 = CH2
For example, Polypropylene (PP) consists of propylene monomer (CH2 = CH - CH3)
Monomer: CH2 = CH - CH3
Repeating unit: -CH2 - CH(CH3)-
Example: Polyvinylchloride consists of vinyl chloride monomer (CH2 = CHCl)
Chloroethene is an ethene molecule in which one of the hydrogen atoms is replaced by a chlorine atom. It is called vinyl chloride. Polymerising vinyl chloride gives polychloroethene. Its commercial name is polyvinylchloride (PVC).
- n\ CH2 = CHCl → (-CH2 - CHCl -)n
12.1.2 Condensation polymers:
Condensation polymers are formed in a condensation reaction where each time a bond is formed between two monomers, a small molecule (often water) is released. Some polymers form in a different way than addition polymers. If one monomer contains a -OH group and the other -H, then they can be joined by eliminating a molecule of water. This reaction is called a condensation reaction. This type of polymerisation process is called condensation polymerisation. Condensation polymers are usually polyamides or polyesters formed by the reaction of functional groups (e.g. carboxyl and amino in polyamides or carboxyl and hydroxyl group in polyesters) with the removal of a small molecule such as water.
Repeating units: In condensation polymers, the repeating unit usually consists of two different types of monomers, each of which forms the polymer backbone with functional groups that react to form the polymer and release small molecules.
Example: Polyesters such as polyethylene terephthalate (PET) are formed from terephthalic acid (HOOC-C6H4-COOH) and ethylene glycol (HO-CH2-CH2-OH).
- Monomers: terephthalic acid and ethylene glycol (a diol)
- Repeating unit: -OC - C6H4 - COO - CH2 - CH2 - O-
- Released molecule: water (H2O)
Example: Polyamides such as nylon-6,6 are formed from hexamethylenediamine (H2N - (CH2)6 - NH2) and adipic acid (HOOC - (CH2)4 - COOH)
- Monomers: hexamethylenediamine and adipic acid
- Repeating unit: -NH - (CH2)6 - NH - CO - (CH2)4 - CO-
- Released molecule: water (H2O)
Concept Assessment Exercise 12.1:
- What type of bond is involved in the formation of addition polymers?
- What is released during the formation of addition and condensation polymers?
- Give an example of a condensation polymer.
- How do these building blocks come together to form polymers?
60-Second Revision
- Polymers = large molecules from many monomers.
- Polymerisation = joining of monomers.
- Two types: addition and condensation.
- Addition polymers: no small molecule released; monomers have double/triple bonds.
- Condensation polymers: small molecule (often water) released; monomers have functional groups.
- Examples:
- Addition: Polyethylene, Polypropylene, PVC.
- Condensation: PET, Nylon-6,6.
- Repeating unit: addition = same as monomer with single bonds; condensation = two different monomers.
- Polyesters = ester linkages.
- Polyamides = amide linkages.
- Polyethylene: n\ CH2=CH2 → (-CH2-CH2-)n
- Polypropylene: n\ CH2=CH-CH3 → (-CH2-CH(CH3)-)n
- PVC: n\ CH2=CHCl → (-CH2-CHCl-)n
- ⚠️ Warning: addition polymers do not release any small molecule, while condensation polymers release a small molecule (often water).
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Revision Zone
Review the key facts, formulas and checks before you move on.12.1.2 Condensation Polymers
Sticky Notes · Quick Revision
Key Point 1
- Polymers = large molecules from many monomers.
Key Point 2
- Polymerisation = joining of monomers.
Key Point 3
- Two types: addition and condensation.
Key Point 4
- Addition polymers: no small molecule released; monomers have double/triple bonds.
Key Point 5
- Condensation polymers: small molecule (often water) released; monomers have functional groups.
Key Point 6
- Examples:
Key Point 7
- Addition: Polyethylene, Polypropylene, PVC.
Key Point 8
- Condensation: PET, Nylon-6,6.
Key Point 9
- Repeating unit: addition = same as monomer with single bonds; condensation = two different monomers.
Key Point 10
- Polyesters = ester linkages.
Key Point 11
- Polyamides = amide linkages.
Key Point 12
- Polyethylene: n\ CH2=CH2 → (-CH2-CH2-)n
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