Polymerization Reactions

What is Polymerization?

Polymerization is a process in which very small molecules, called monomers, combine chemically with each other to produce a very large chainlike molecule, called a polymer.

The First Polymerization

The first synthetic polymer was discovered in 1909 by Leo Backeland, a Belgian-born US Chemist.

It was marketed under the trademark Bakelite, which was made from phenol and formaldehyde.

It became an important plastic and resin for adhesives, and paints.

There are two main types of Polymerization reactions:

Addition

Condensation

Polymerization Types

2 + 2Think water, although that is not always the case

Addition Polymerization

The monomer molecules may be all alike, or they may represent two, three, or more different compounds. The Addition Reaction involves only double and single bonded compounds.

In Addition Polymerization, monomers form without a by-product, such as water. The structure has one structural unit, or monomer, that occurs repeatedly.

Through polymerization of ethylene (ethene), CH2CH2, the structure of the polymer can be represented by -(CH2CH2)n- where n can be several thousand. Example:

H H H H H H H H H H H H | | | | | | | | | | | | C=C + C=C + C=C => :C-C:C-C:C-C: | | | | | | | | | | | |H H H H H H H H H H H H ethylene part of polyethylene

Addition Polymerization

OR -(CH2CH2)n- Because of this, polymers have incredible molar masses up to millions of grams per mole.

Addition Polymerization

The elastic property of rubber is due to the flexibility of the long chain molecules.

In 1839, American chemist Charles Goodyear discovered that natural rubber could be cross-linked with sulfur. This would prevent the long chains from slipping.

This process was known as vulcanization.

It “paved the way” for many practical and commercial usage, including using vulcanized rubber for automobile tires.

Free Radical PolymerizationFree-Radical Addition is another type of polymerization reaction. This is when the polymer is induced by an initiator, which is a compound that produces free radicals.

Free-radicals are species that have an unpaired electron.

Note: Free radicals can damage human tissue…heard of anti-oxidants?

In condensation polymerization, two functional groups of two different monomer molecules are joined together which produces a small molecule such as water.

Remember the water?

The monomers bond where the hydrogen atoms were taken out to produce water. In order to become a condensed polymer, the monomer molecules must have at least two functional groups.

Condensation Polymerization

The reaction between a carboxylic acid and an alcohol creates an ester.

If the carboxylic acid and the alcohol were the monomers of the polymer, during polymerization, they would create polyester, and produce water.

Condensation Polymerization

Condensation Polymerization

Example of condensation polymerization: Curing of concrete

There are several types of materials that form by Condensation Polymerization, including nylon, polyesters, rayon, and spandex.