Without polymers, mankind couldn't exist. People use manmade plastics such as polypropylene and polyvinyl chloride (i.e., PVC) in hospitals, schools and their own homes. Yet, man-made plastic accounts for only a small percentage of polymers. Rubber and cellulose, which are natural polymers, are used to make everything from tires to cellophane to rayon. Deoxyribonucleic acid (i.e., DNA) and protein are also natural polymers.

As important as polymers are, they wouldn't exist without monomers, which are small, single molecules such as hydrocarbons and amino acids. These monomers bond together to form polymers. The process by which these monomers bond is called polymerization.

Polymerization isn't a complicated subject, but the ways in which monomers are put together vary so much that scientists find it easier to have more than one system of describing polymerization. One system of separating polymerization processes asks the question of how much of the original molecule is left when the monomers bond. In "addition polymerization", monomers are added together with their structure unchanged. This kind of polymerization could be likened to a kid playing with a Lego set. The Legos put together make a larger structure, but in the end the individual Legos are still discernable.

Not so in condensation polymerization. This process results in a polymer that is less massive than the two or more monomers that joined to form it. This happens because not all of the original monomer is allowed to stay on the polymer. Hydrogen chloride and water are usually thrown from the mix when polymers form in this manner. A good analogy might be what happens when kids try to make a popsicle-stick village. The popsicle itself has to be discarded (most often through eating!) in order to be able to use the stick itself.

While the condensation versus addition systems of describing polymerization may be useful, it is not the only way to see how polymers might form. Another way of explaining how monomers form polymers involve observing how the monomers combine with one another. In chain growth polymerization, one monomer is added to the collection at a time until a polymer is formed. This is the simplest process of polymerization. A more complicated process is called step-growth polymerization. Here, it isn't just one monomer joining the party at a time. It can happen that way, but it's also possible for a group of monomers to show up together. Eventually, there will be enough monomers to create a polymer.

Polymerization is a necessary process. Only through this forming of larger molecules could the human brain exist. In actuality, nothing at all could exist without polymerization, for without a brain to experience life and define its processes, there would be no reason to exist.