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 Think 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 | | | | | | C=C + C=C + C=C => :C-C:C-C:C-C: | | | | | | 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 Polymerization  Free-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

 Example of condensation polymerization: Curing of concrete  There are several types of materials that form by Condensation Polymerization, including nylon, polyesters, rayon, and spandex.