Themes > Science > Chemistry > Organic Chemistry > Organic Chemistry Index > Polymers > Addition Polymerization

Addition polymerizations are reactions where a polymer is formed from its monomers without leaving other molecules behind.

Polyethylene is an addition polymer: each unit adds onto the chain without leaving any residue behind. The polyethylene is made up of many ethylene molecules, CH2=CH2, known as ethylene monomers. Two ethylene molecules can form a bond to make

CH2=CH2 + CH2=CH2 -> CH2=CH-CH2-CH3
This is known as a dimer, a molecule made up of two repeat units. Adding another ethylene molecule will form a trimer,
CH2=CH-CH2-CH3 + CH2=CH2 -> CH2=CH-CH2-CH2-CH2-CH3
then a tetramer, and so on until a very long chain of (CH)2 units is formed. The molecular weight of polyethylene you buy in a store ranges from 100's of thousands to millions.


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