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Formation and Hydrolysis of Condensation Polymers

Definition

Condensation polymers

Condensation polymers are created when monomers with two reactive functional groups join together, releasing a small molecule such as water or hydrogen chloride (HCl).

This contrasts with addition polymerization, where no by-product is formed.

How Does Condensation Polymerization Work?

In a condensation reaction, two monomers react to form a covalent bond, creating a polymer chain.
Each monomer must have at least two functional groups to allow for chain growth.
The small molecule released during this reaction is a by-product of the bond-forming process.

Analogy

Think of condensation polymerization like building a chain of paperclips: each clip represents a monomer, and the small piece of metal you snip off when linking them is the by-product.

Polyamides

Polyamides are formed through the reaction between a dicarboxylic acid and a diamine.
The functional groups involved are the carboxyl group (-COOH) and the amino group (-NH2), which form an amide linkage (-CONH-).

Example

Nylon-6,6 is made by reacting hexanedioic acid with hexane-1,6-diamine. $$\mathrm{HOOC{-}(CH_2)_4{-}COOH} + \mathrm{H_2N{-}(CH_2)_6{-}NH_2}$$ $$\rightarrow \mathrm{[-CO{-}(CH_2)_4{-}CO{-}NH{-}(CH_2)_6{-}NH-]_n} + (n-1)\,\mathrm{H_2O}$$

Polyesters

Polyesters are formed through the reaction between a dicarboxylic acid and a diol.
The functional groups involved are the carboxyl group (-COOH) and the hydroxyl group (-OH), which form an ester linkage (-COO-).

Example

PET is made by reacting terephthalic acid with ethane-1,2-diol. $$\text{HOOC-C}_6\text{H}_4\text{-COOH} + \text{HO-(CH}_2\text{)_2-OH}$$ $$\rightarrow \text{[-CO-C}_6\text{H}_4\text{-CO-O-(CH}_2\text{)_2-O-]}_n + (n-1) \text{H}_2\text{O}$$

Tip

Condensation polymers often alternate between two types of monomers, creating a repeating ABAB pattern in the polymer chain.

Properties of Condensation Polymers

Condensation polymers are widely used due to their diverse properties:

Polyamides like nylon are strong, elastic, and resistant to abrasion, making them ideal for textiles, ropes, and bulletproof vests.
Polyesters like PET are lightweight, durable, and resistant to moisture, commonly used in packaging, clothing, and even 3D printing.

Example

Kevlar, a type of polyamide, is used in bulletproof vests due to its strong hydrogen bonding between polymer chains, which enhances its tensile strength.
Similarly, PET is used in water bottles for its lightweight and shatter-resistant properties.

Hydrolysis of Polymers: Breaking Down the Chains

While condensation reactions build polymers, hydrolysis breaks them down.

Definition

Hydrolysis

Hydrolysis is the reverse of condensation polymerization, where water reacts with the polymer to break the covalent bonds between monomers.

How Does Hydrolysis Work?

In hydrolysis, water molecules interact with the functional groups in the polymer, splitting the bonds that hold the monomers together.

Biological Hydrolysis: Proteins and Polysaccharides

Proteins, which are natural condensation polymers made of amino acids, are broken down by hydrolysis in living organisms.
Enzymes like proteases catalyze this process, breaking the peptide bonds into individual amino acids.
Polysaccharides like starch are also broken down via hydrolysis into monosaccharides (e.g., glucose), providing energy for cellular processes.

Example

Hydrolysis of a Polypeptide

$$
\text{[-NH-(CH}_2\text{)_2-CO-]}_n + (n-1) \text{H}_2\text{O} \rightarrow \text{n H}_2\text{N-(CH}_2\text{)_2-COOH}
$$

Note

Biodegradable plastics are designed to hydrolyze more easily, allowing microorganisms to break them down into harmless substances.

Comparing Addition and Condensation Polymers

Feature	Addition polymers	Condensation polymers
Formation	No by-products formed	Small molecule released (water)
Monomers	Contain a carbon-carbon double bond	Contain two functional groups
Examples	Polyethene, PVC	Nylone, PET
Environmental impact	Often non-biodegradable	Some are biodegradable

Common Mistake

Do not confuse addition and condensation polymerization.
Addition polymers form from alkenes, while condensation polymers require functional groups like $-COOH$ and $-OH$.

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Introduction to Condensation Polymers

A polymer is a large molecule made up of repeating smaller units called monomers. In condensation polymerisation, each time two monomers join together, a small molecule (like water) is lost. This is different from addition polymerisation where no molecules are lost.

DefinitionCondensation polymerisationA type of polymerisation where monomers join together with the loss of a small molecule, usually water.

AnalogyThink of condensation polymerisation like building a necklace where each bead (monomer) is connected by a knot, and every time you tie a knot, you cut off a small piece of string (the water molecule).

ExampleWhen glucose molecules join to form starch, water is released in a condensation reaction.

S2.4.6 Condensation polymers (Higher Level) Notes

Formation and Hydrolysis of Condensation Polymers