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S1.1 - Introduction to the particulate nature of matter S1.2 - The nuclear atom S1.3 - Electron configurations S1.4 - Counting particles by mass - The mole S1.5 - Ideal gases S2.1 - The ionic model S2.2 - The covalent model S2.3 - The metallic model S2.4 - From models to materials S3.1 - The periodic table - Classification of elements S3.2 - Functional groups - Classification of organic compounds R1.1 - Measuring enthalpy changes R1.2 - Energy cycles in reactions R1.3 - Energy from fuels R1.4 - Entropy and spontaneity AHL R2.1 - How much? The amount of chemical change R2.2 - How fast? The rate of chemical change R2.3 - How far? The extent of chemical change R3.1 - Proton transfer reactions R3.2 - Electron transfer reactions R3.3 - Electron sharing reactions R3.4 - Electron-pair sharing reactions

S2.4 - From models to materials

2.4.1 The Bonding Continuum 2.4.2 Using the Bonding Triangle 2.4.3 Alloys 2.4.4 Polymer and Plastic Properties 2.4.5 Addition Polymerization 2.4.6 Condensation Polymerization (AHL)

Condensation Polymers HL Only

Specification Reference S2.4.6

Quick Notes:

  • Condensation polymers form when monomers with two functional groups react, releasing a small molecule (usually water).
  • Each linkage between monomers forms through a condensation reaction.
  • Two main types:
    • Polyamides: formed from amines and carboxylic acids
    • Polyesters: formed from alcohols (diols) and carboxylic acids (dicarboxylic acids)
  • You must be able to:
    • Deduce the repeating unit of a polyester or polyamide
    • Recognize monomers from a polymer structure
  • Biological macromolecules (proteins, carbohydrates, DNA) also form by condensation and break down by hydrolysis.

Full Notes

What Is a Condensation Polymer?

A condensation polymer forms when two different functional groups on monomers react to form a link and release a small molecule, commonly water or HCl.

IB Chemistry overview diagram of condensation polymerization showing di-functional monomers linking with elimination of a small molecule such as water.

The reaction is stepwise, producing long chains with repeating functional group linkages.

Types of Condensation Polymers

Polyesters

Formed from diols (–OH) and dicarboxylic acids (–COOH).

IB Chemistry schematic showing diol and dicarboxylic acid forming an ester linkage with elimination of water to give a polyester.

Linkage: –COO– (ester bond)

Example Terylene / PET formation

Monomers: ethane-1,2-diol + benzene-1,4-dicarboxylic acid

Polymer: Terylene, PET (polyethylene terephthalate)

IB Chemistry example of PET formation from ethane-1,2-diol and benzene-1,4-dicarboxylic acid with ester links repeating along the chain.

Repeating unit: –[–O–CH2–CH2–O–CO–C6H4–CO–]–n

Polyamides

Formed from diamines (–NH2) and dicarboxylic acids (–COOH).

IB Chemistry schematic showing diamine and dicarboxylic acid condensing to form an amide linkage with loss of water to give a polyamide.

Linkage: –CONH– (amide/peptide bond)

Example Nylon-6,6 formation

Monomers: hexane-1,6-diamine + hexanedioic acid

Polymer: Nylon-6,6

IB Chemistry example of Nylon-6,6 formation from hexane-1,6-diamine and hexanedioic acid forming repeating amide links.

Repeating unit: –[–NH–(CH2)6–NH–CO–(CH2)4–CO–]–n

Drawing and Identifying Repeating Units

To draw a repeating unit:

  1. Remove –H from amine or alcohol group.
  2. Remove –OH from carboxylic acid group.
  3. Join them with either –COO– (ester) or –CONH– (amide) linkage.

To identify monomers:

  1. Locate the repeating linkage (ester or amide).
  2. “Break” the polymer at that point.
  3. Add back the appropriate –OH or –NH2 groups.

Biodegradable Condensation Polymers

Unlike poly(alkenes), polyesters and polyamides contain functional groups (–COO– and –CONH–) that are susceptible to hydrolysis.

IB Chemistry diagram showing hydrolysis of condensation polymer linkages by acid, base, or enzymes leading to chain breakdown.

These polymers can be broken down:

Polyesters (e.g. PLA – polylactic acid) and polyamides (e.g. nylon, proteins) are therefore biodegradable and suitable for eco-friendly uses.

For example Polyesters can be broken down into diocarboxylic acids and diols.

IB Chemistry schematic of polyester hydrolysis regenerating a diol and a dicarboxylic acid from the ester link.

Biological Condensation Polymers

Polymer Monomers Linkage Breakdown by…
Proteins Amino acids Amide (peptide) Hydrolysis
DNA Nucleotides Phosphodiester Hydrolysis
Starch Glucose Glycosidic Hydrolysis

Linked Course Questions

Structure 3.2 – Linked Course Question

What functional groups in molecules can enable them to act as monomers for condensation reactions?

Monomers for condensation reactions must contain two functional groups that can react with each other, such as –COOH with –OH (to form esters) or –COOH with –NH2 (to form amides). These allow the monomers to link together, forming polymers while eliminating small molecules like water.

Summary