Write a short note on step-growth polymerization.

(N/A) Step-growth polymerization generally involves a repetitive condensation reaction between two different bi-functional or tri-functional monomeric units.
These polycondensation reactions may result in the loss of simple molecules such as $H_2O$,$ROH$,$HCl$,etc.,and lead to the formation of high molecular mass condensation polymers.
In these reactions,the product of each step is again a bi-functional species,and the sequence of condensation continues.
Since each step produces a distinct functionalized species and is independent of others,this process is called step-growth polymerization.
The formation of Terylene or Dacron by the interaction of ethylene glycol and terephthalic acid is an example of this type of polymerization:
$nHO-CH_2-CH_2-OH + nHOOC-C_6H_4-COOH \rightarrow -[O-CH_2-CH_2-O-CO-C_6H_4-CO]_n- + 2nH_2O$