by Susana B. Grassino
Polymers are a very special kind of compounds, which don't behave like
small molecules do. And they don't not only because of their big molecular
size. Precisely that "big size" sets off three
unique properties that are attributed only to giant molecules.
What properties, you might ask? Surely you've seen them before. Those properties depend on differences, and applications depend on the properties, or better, the combination of properties that each polymer has.
OK, but what are those properties, anyway? In case you haven't visited the
page in which they're explained, we can
summarize them again:
All these properties determine the diverse states of macromolecular aggregation that polymers show.
For instance, could you imagine a polymer in its gaseous state? Don't worry. There're not gaseous polymers. Such large molecules have so strong intermolecular forces holding them together, that you would need to heat them at no less than 500�C to achieve evaporation. But at those high temperatures you would no longer have polymers, but a big mass of decomposed or carbonized monomers.
Even the liquid state is rarely observed in polymers. Most of the time the compound exhibits a rubber-like consistency, and becomes viscous when the temperature is gradually increased.
Solid polymers usually exist as amorphous
glasses. However, when a certain order in their chain structure is
present, such polymers can crystallize, like fibers, polyketones
or syndiotactic polystyrene.
All solid polymers display a high state of aggregation, unlike macromolecular solutions, particularly the dilute ones. That's why specific studies of shape and size of each polymer chain have been carried out.
Polymer solutions are highly viscous, but if you increase their
concentration, they become so viscous that, at a certain point, intermolecular forces come into play again and the liquid character vanishes. We are talking now about a "gel" instead of a solution.
Interesting, huh?
Would you like to learn more? Then let's look at each state of aggregation separately:
