Condensation or Step Growth Reaction

Condensation reaction is one where two monomers or short functional macromolecule segments combine together to form a long segment, usually with the elimination of a small molecule such as water or alcohol. For this to take place, each reacting segment must have chemically reactive end groups. The reaction of a pair of snch 

The reaction between a diamine and a dicarboxylic acid to yield a polyamide (or a nylon) is an example of a polycondensation. The basic reaction is shown below. The reaction does not stop here as the product too has the same functional groups and can therefore react with other products to yield chains of different lengths, hi this type of reaction, all molecular species such as monomers, dimers, trimers, and longer chains can react concurrently, yielding chains with high enough Mw values that would make the polymer practically useful  

Since these are equilibrium reactions, the water or other small molecular product needs to be removed from the mixture to encourage the reaction to proceed in the forward direction. Another example is the condensation of bisphenol A monomer 

Phenol-formaldehyde resin, the first all-synthetic plastic (trade name Bakelite) made in 1907, was made via a polycondensation reaction. 

Coupling reactions between monomers can also occur without the loss of a small 

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