Addition Polymers: Structure, Properties, and Applications

Introduction

Addition polymers, also known as chain-growth polymers, form the backbone of modern plastic materials. These remarkable substances are created through a process where simple molecular units (monomers) containing carbon-carbon double bonds combine to form long chains of repeating units.

Formation of Addition Polymers

Addition polymerization occurs through a three-step process involving monomers with carbon-carbon double bonds (C=C). The process requires an initiator and proceeds through the following steps:

1. Initiation

The process begins when an initiator molecule, such as hydrogen peroxide ($\text{H}_2\text{O}_2$), decomposes to form free radicals. These highly reactive species contain unpaired electrons:

$\text{H}_2\text{O}_2 \rightarrow 2\text{OH}^{\bullet}$

2. Propagation

During this stage, the free radical attacks the carbon-carbon double bond of a monomer, creating a new radical that can continue the chain reaction:

$\text{R}^{\bullet} + \text{CH}_2=\text{CH}_2 \rightarrow \text{R}-\text{CH}_2-\text{CH}_2^{\bullet}$

3. Termination

The chain growth stops when two radicals combine:

$\text{R}-(\text{CH}_2-\text{CH}_2)_n^{\bullet} + ^{\bullet}(\text{CH}_2-\text{CH}_2)_m-\text{R} \\\rightarrow \text{R}-(\text{CH}_2-\text{CH}_2)_{n+m}-\text{R}$

Common Addition Polymers

Polyethylene (PE)

Two major forms exist:

Polyvinyl Chloride (PVC)

Polystyrene (PS)

Polytetrafluoroethylene (PTFE)

Environmental Considerations

While addition polymers have revolutionized modern life, their persistence in the environment presents challenges. Proper recycling and disposal are essential for sustainable use of these materials.