These two molecules join together to form both the intended product and a waste product. Polyamides, or Nylons, were discovered in 1938 by some crazy guy at DuPont corporation who made a mistake. Since then, nylons have been used as a replacement for most textiles, as they are generally stronger, and last longer. Nylons, or polyamides are made from reactions between diacids and diamines. Nylon can also be formed as a homopolymer, given the monomer has an amino group at one end, and an acid at the other, such as to form a bond between monomers with a reaction similar to the one above.
Polyesters are another widely used polymer.
They are formed through the reaction of esters and a diacid. Here we can see an example of the reaction that forms Dacron, the polymer of terepthalic acid and ethylene glycol. Using a great deal of heat, the molten product is spun into fibers for clothing, ropes, tire cord, or Mylar film. Polycarbonates are, most simply, esters of carbonic acid. A carbonic acid is a diacid, and it will bind with a suitable diol to form a polymer, in the form of an ester.