Polymerisation by the opening of a double bond e.g. ethylene

The number of molecules combined, n, may vary at the low end between 10 - 20. The products are then called telomers or oligomers. For pol5miers, n is between 1000 and 100000 or more. The polymer growth occurs very rapidly, in seconds or minutes. Thus, fully formed macromolecules exist almost from the beginning of the reaction. However, the overall time required for a high conversion of monomer to pol5mier is often several hours. 

Depending on the activation (type of reaction initiation), a differentiation is made between radical and ionic polymerisation  

Initiators very often need special care since they are either potentially explosive like peroxides or react vigorously with water and are flammable such as metal alkyls. Usually, initiator concentrations vary and are between 0.1-0.5 wt-%. Dissociation products of the radical initiator are removed from the polymer or built-in, while decomposed metal alkyl residues of the initiator remain in the product and sometimes have an influence on end use properties. 

The actual polymerisation may be carried out in bulk, in water or in organic solvents or dispersants. 

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Figure 2.2 Polymerisation by the opening of a double bond (e.g. ethylene)...

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