S2.4.6 Condensation polymers (Higher Level)

Formation and Hydrolysis of Condensation Polymers

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.

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-).

• Reaction:

$$\mathrm{HOOC}-({\mathrm{CH}}_2{)}_4-\mathrm{COOH}+{\mathrm{H}}_2\mathrm{N}-({\mathrm{CH}}_2{)}_6-{\mathrm{NH}}_2$$ $$\to [-\mathrm{CO}-({\mathrm{CH}}_2{)}_4-\mathrm{CO}-\mathrm{NH}-({\mathrm{CH}}_2{)}_6-\mathrm{NH}-{]}_{\mathrm{n}}+(n-1){\mathrm{H}}_2\mathrm{O}$$

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-).

• Reaction:

$${\text{HOOC-C}}_6{\text{H}}_4\text{-COOH}+{\text{HO-(CH}}_2\text{)\_2-OH}$$ $$\to {\text{[-CO-C}}_6{\text{H}}_4{\text{-CO-O-(CH}}_2{\text{)\_2-O-]}}_n+(n-1){\text{H}}_2\text{O}$$

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.

Hydrolysis of Polymers: Breaking Down the Chains

While condensation reactions build polymers, hydrolysis breaks them down.

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.

Comparing Addition and Condensation Polymers

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