Changes

There are three steps in the formation of a polymer.

There are three steps in the formation of a polymer.

''Initiation''

====Initiation====

A chemical (called the initiator) is added to a substance containing the monomers. It activates one of the monomers (in many cases when alkenes are used the double [[bond]] is split producing two free [[electrons]] which can react with other molecules) allowing polymerization to occur. It is important to note that the initiator is not a catalyst as in most cases it is absorbed into the final product. Common initiators include organic peroxides (used to produce LDPE).

A chemical (called the initiator) is added to a substance containing the monomers. It activates one of the monomers (in many cases when alkenes are used the double [[bond]] is split producing two free [[electrons]] which can react with other molecules) allowing polymerization to occur. It is important to note that the initiator is not a catalyst as in most cases it is absorbed into the final product. Common initiators include organic peroxides (used to produce LDPE).

''Propagation''

====Propagation====

The active monomer activates another unit (eg by causing its double bond to split), as there are now four free electrons a covalent bond can form between the two units and two electrons (one on each atom) will be left to combine with other units. This process continues and the chain grows in size with every unit added. During propagation side branching can occur, in which monomers start a secondary chain leading off the first. These chains can affect the properties of the end polymer, and can be controlled depending on the conditions in which polymerization occurs.

The active monomer activates another unit (eg by causing its double bond to split), as there are now four free electrons a covalent bond can form between the two units and two electrons (one on each atom) will be left to combine with other units. This process continues and the chain grows in size with every unit added. During propagation side branching can occur, in which monomers start a secondary chain leading off the first. These chains can affect the properties of the end polymer, and can be controlled depending on the conditions in which polymerization occurs.

''Termination''

====Termination====

This is when propagation of a chain or a section of the chain is halted because of a reaction with a unit which does not produce a free electron (and hence cannot react with other units). An example of a terminator is oxygen, which will form a covalent bond with the chain but will not have any free electrons to continue reacting.  

This is when propagation of a chain or a section of the chain is halted because of a reaction with a unit which does not produce a free electron (and hence cannot react with other units). An example of a terminator is oxygen, which will form a covalent bond with the chain but will not have any free electrons to continue reacting.

===Reactions Involved in Basic Polymerization===

===Reactions Involved in Basic Polymerization===