The phenol-formaldehyde polymers are the oldest commercial synthetic polymers, first introduced around 100 years ago. Their inventor, Leo Bakeland, had no idea what was happening in his reaction kettles, but he was able to work out conditions to produce a tough, light, rigid, chemically resistant solid from two inexpensive ingredients. He soon became a rich man, in the same class as the famous industrialists of the time like Alfred Nobel, Henry Ford, Andrew Carnegie, George Eastman, etc.
The actual chemistry is complicated, and still not competely understood. The polymers are usually thermosetting (i.e., crosslinked), and their insolubility limits the analytical techniques that can be brought to bear. The main reaction is the production of methylene bridges between aromatic rings, as shown below. Many side reactions also occur, and some of these give phenol-formaldehyde polymer its dark color.
Of course, these crosslinked polymers cannot be melted or dissolved, so their synthesis must be conducted in molds for the actual product. In practice, the polymerization is usually carried out to somewhere below the gel point in a separate reactor, and then the "pre-polymer" is transferred to the mold, where the reaction is completed.
Urea or melamine can be substituted for phenol. Methylene bridges can also be formed between the nitrogen atoms, giving rise to chemical relatives of the phenol-formaldehyde polymers. The urea and melamine based materials have much less color, and so are useful for decorative applications such as dinner plates and countertop materials (FormicaTM).
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