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. Polyurethanes are very similar to polycarbonates, in that they as well are variations on a carbonic acid ester.
Urethanes are esters of carbamic acid, a half amide of carbonic acid.
However, a urethane reaction rarely uses urethane as a reactant, but more stable isocyanate, which will react with an alcohol or phenol to yield carbamate ester, a urethane. Sterreochemistry of Polymers Because a polymer generally has many chiral atoms, it can be inferred that there could be many enantimers of a polymer. It is for this reason that chemists classify polymers by the orientation of their constituents on the carbon chain. A polymer is isotactic if the R group is on the same side of the polymer backbone. A polymer is syndiotactic if the R groups alternate sides from carbon to carbon.