Besides a polymer, what is a by-product produced during a synthesis reaction with two monomers?

Besides a polymer "water molecule" is a by-product produced during a synthesis reaction with two monomers.

Explanation:

Polymer reaction or polymerization is the process in which two or more than two monomers react with each other to form a polymer with byproduct, which depends upon type of reaction and reactants involved.

For an instance like the hydrogen of one monomer interacts with the hydroxyl group of another monomer in a dehydration synthesis reaction, forming a water molecule as a byproduct. The monomers also share electrons and form covalent bonds. A chain of repeated monomers forms a polymer, as additional monomers join.