However, we will try to keep this review material interesting and a bit different by looking at how ideas about the nature of matter developed, but you will still have to do some work and think a little bit. Then we will be into the heart of this subject – how are polymers made and what is it about their structure that gives them their extraordinary range of useful properties. But, let's start right at the beginning; what is a polymer?
Polymers are very large molecules (sometimes called macromolecules) that are built up of smaller units called monomers. (The word polymer comes from the Greek for many units.) You may already know this, or your language skills are such that you guessed. Other common definitions are given below.
 

All disciplines develop their own ways of abusing the English language, psychology and sociology come to mind (personal value judgment), and ours is no exception, but we believe these definitions are almost self-evident. So, how big are polymers?

Bloody enormous! See the figure on the left, above? This is a picture representation of a chain, where each one of the beads that have been strung together represents a chemical unit of some sort. Some of our physicist friends have taken to calling these types of pictures cartoons, but that just makes us think of Saturday mornings and Bugs Bunny. Anyway, as polymers go, this is actually a very short chain, or as we say, it has a low molecular weight.

On the right of this “beads on a string” model is another short chain. Instead of beads, we show methylene (CH2) units in the form of balls and sticks linked together to form a linear chain (i.e., one that has no branches – more on this later).

Chemically, we actually string ethylene units, not methylene (CH2) units, together during synthesis:
 

Then, if there are only 200 ethylene units in this chain (i.e., it is a 200-mer), its molecular weight is only 5,600 (= 28 x 200). (If you've forgotten how to calculate molecular weights from atomic weights, don't sweat it just yet. We'll make you sweat it later!) Commercially produced polyethylenes often have molecular weights in the hundreds of thousands. To give you a feel for this, imagine that each ethylene unit has a length of 1 inch instead of a couple of angstroms (1 angstrom = 10–8 cm). The length of a fully stretched out chain of molecular weight 420,000 (15,000 polymerized ethylene units) would then be almost one-quarter of a mile long! These are very big molecules indeed.

Many of the physical properties of polymers are simply a consequence of their large size. To also get a feel for this, let’s consider building a simple hydrocarbon chain one carbon atom at a time, filling up all the unsatisfied valences with hydrogen atoms, as below.
 

If we have just one carbon atom (and hence four hydrogens), we have the gas perhaps because it not only emanates from the ground, but also the rear end of cows. The next three in the series are ethane, propane and butane, which have, respectively, two, three and four carbons in their chains. These are also gases at ambient temperatures and pressures, the latter two being commonly used for heating and cooking. Liquids, commonly used as auto and jet fuels typically have carbon chain lengths of 6–12. As we increase the carbon chain lengths further, the viscosity increases and we go from liquid materials used for baby oils, to “semi-solid” materials used as soft and hard candle waxes. At even higher carbon chain lengths, typically exceeding 30,000, we encounter hard, solid polyethylenes.

Finally, it is important to recognize that all polymers, be they natural or synthetic, are simply giant long chain molecules or macro-molecules. It's all chemistry, and there really is no basic difference between a natural or synthetic polymer, in that both obey the same physical laws. Cellulose, for example, the natural polymer that is found in cotton and numerous other plants (and the most abundant polymer on the face of the planet), is a long chain macromolecule composed of carbon, hydrogen and oxygen. So is the synthetic polyester fiber, poly(ethylene terephthalate) (PET). It's just that the arrangement (architecture) of the atoms in the two polymer chains is different. However, it is common practice to distinguish between natural and synthetic polymers and also classify them in terms of plastics, fibers, elastomers, composites, paints, adhesives, etc. Various types of materials and some of their natural and synthetic counterparts are shown in the table below. We will compare and contrast the structure of some natural and synthetic polymers in later chapters.