Polymerization :

Polymerization is the process of mixing numerous tiny molecules known as monomers into a covalently bonded chain or network. Throughout the polymerization procedure, some chemical groups can be missing from each monomer. This is the case, for example, in the polymerization of PET polyester. The monomers are terephthalic acid (HOOC-C6H4-COOH) and ethylene glycol (HO-CH2-CH2-OH) but the repeating unit is -OC-C6H4-COO-CH2-CH2-O-, which corresponds to the combination of the two monomers with the loss of two water molecules. The distinct section of each monomer that is incorporated into the polymer is recognized as a repeat unit or monomer residue.

Lab synthetic methods are usually separated into two groups, first group is step-growth polymerization and second is chain-growth polymerization.
The essential modification between the two is that in chain growth polymerization, monomers are added to the chain one at a time only, such as in polyethylene, whereas in step-growth polymerization chains of monomers might mix with one another directly, such as in polyester.
Though, the latest methods such as plasma polymerization do not fit neatly into either category.
Synthetic polymerization reactions may be carried out with or without a catalyst. Laboratory synthesis of biopolymers, especially of proteins, is an area of intensive research.