1. Addition Polymers. When the monomer units are repeatedly added to form long chains without the elimination of any by-product molecules, the product formed is called addition polymer and the process involved is called addition polymerisation. The monomer units are unsaturated compounds and are usually the derivatives of alkenes. The molecular formula and hence the molecular mass of the addition polymer is an integral multiple of that of the monomer units. Some examples of addition polymerisation are:
2. Condensation Polymers. In this type of polymers, the monomers react together with the elimination of a simple molecules like H2O, ROH or NH3, etc. The reaction is called condensation and the product formed is called condensation polymer.
As the process involves the elimination of molecules, the molecular mass of the polymer the integral multiple of the monomer units. For example 6,6 is a condensation polymer of hexamethylene and adipic acid.
Some other examples of condensation polymers are:
Dacron (polyester): A polymer of ethylene glycol and terepthalic acid.
Bakelite: A polymer of phenol andformaldehyde.
Polyurethanes. These are the condensation polymers of toluene-2, 6-diisocyanate and ethylene glycol. During polymerisation a low boiling liquid such as Freon-11 are added to reaction mixture. The heat liberated during polymerisation causes vaporisation of low boiling liquid producing bubbles which converts viscose polymer to form polyurethane foams