By definition, a polymer is a compound made of many units linked together, usually in a long chain. Indeed, the word polymer comes from linking the prefix poly, which means many, with mer which means units.
The individual units in a polymer are called monomers. Two linked together are called a dimer. A short chain of units is called an oligomer. And nature employs all of these different types of units to build the world around us.
For example, glucose is a monomer which is used to generate the polymers starch and cellulose.
The way the individual sugar units are joined together distinguishes between these two naturally occurring polymeric compounds.
In cellulose, the linkage results in long straight chains which are difficult to digest. In starch, branching occurs with the result that starches are a suitable source of complex carbohydrates.
Even so, starch is really just a whole bunch - say, 10,000 or so - sugar molecules joined together. Our digestive enzymes and processes are capable of peeling off each sugar molecule one at a time for our use in generating energy. The difference between eating glucose and starch is just a matter of the time it takes for the carbohydrate to be made available to the body.
Eating glucose, the molecules come in a single rush. Eating starch, the molecules arrive over a protracted length of time.
Table sugar, or sucrose, is actually a dimer composed of glucose and fructose. In this case, it is given the special name of a disaccharide. Starch and cellulose are both cases of polysaccharides. They are built of the same unit over and over.
DNA is another example of a polymer but, in this case, there are four different types of monomers and each is much more complex than a simple sugar.
The monomers are called nucleotides and are composed of a nucleic base (adenine, cytosine, guanine and thymine), a sugar (deoxyribose) and a phosphate group. Linkage between the monomers is through the phosphate-sugar-phosphate backbone. The nucleic bases dangle from this chain much like the charms on a bracelet.
RNA is a similar polymer with a ribose sugar, but RNA is also the messenger which controls the synthesis of proteins. Proteins are composed of 20 or so different monomers (called amino acids) linked through chemical bonds. They are short chain polymers with typically only a 100 different monomeric groups.
However, the functionality of proteins allows them to act as catalysts to generate all sorts of other chemical compounds, including polymers such as starch and cellulose.
Nature has taken full advantage of polymers to generate much of the living world. Indeed, even the inorganic compounds such as clays and glasses can be thought of as polymeric substances. Nature loves polymers.
Perhaps it is not surprising we have taken advantage of polymers in constructing materials for our modern civilization. Compounds such as polyethylene and polypropylene - polymers generated from the monomers ethylene and propylene, respectively - have come to dominate our lives.
We tend to call these polymers plastics, although that is more of a description of their malleability than their structure. A plastic is something which is moldable with heat or pressure.
We also seem to have a love-hate relationship with these compounds. On the one hand, they are very long lasting and persist for a long time in our environment.
They are virtually indestructible under normal conditions which allow their use in pipes, clothing and floatation devices just to name a few.
On the other hand, the persistence of these compounds has resulted in polymeric items floating in the world's oceans for decades. Whiteboard markers, plastic bags, and tiny bits of plastic sheets have been found in the water column throughout the oceans. Often these items end up in the stomachs of birds and fishes, as they mistake them for food.
We depend on a whole range of substances for pretty much everything we use. It has been estimated that over 80 per cent of commercial products on the market today contain some form of plastic - everything from kid's toys to facial scrubs to the Boeing 787 Dreamliner - polymer-based composites make up more than half the weight of the plane.
New compounds are being designed which are more environmentally friendly.
The blending of cellulosic polymers with petroleum-based molecules can result in plastics which have suitable properties for a number of applications and will breakdown in a matter of years in the environment. However, these new compounds are expensive and energy intensive to produce with large carbon footprints. Scientists are working on better manufacturing techniques.
Whether natural or artificial, polymeric substances are here to stay. They form the backbone of much of our living world.
Increasingly, they are finding ways into a multitude of manufactured items and are the backbone of modern civilization.
