One of the ways in which monomers are converted to polymeric form is by [DCE 2002]
Condensation reaction between monomers
If you remember the condensation reaction, it is the process where a water molecule is lost when 2 monomer units combine together and we get a dimer unit and eventually a full polymeric unit after loss of many, many water molecules.
This is one of the ways in which a polymer can be created. Nylon-6,6 is a good example of this process. Here is the equation for your reference.