Polymers Part I

Polymers are fascinating molecules, of commercial and environmental significance.  Modern polymer chemistry reflects an incredible diversity of reactions, functions and structures, most of which defies traditional classification.  In their simplest form, polymers are molecules made up of many repeating units called monomers, similar to how a necklace might be made of different beads.   Polymers and plastics pervade our planet in an alarming way – as functional materials and polluting waste.  But it was not always that way – polymers are very much a 20th century phenomena.

Prior to the 1900s, polymers were thought to be aggregates of small molecules.  Actually, chemists believed that there was a finite size beyond which molecules would simply fall apart.  There was also the notion that a compound must have one formula, that a compound had to be pure.  For example water was H2O, not H4O2 or H8O4.   The notion that molecules had to be discrete small structures was perhaps an artifact of synthesis and characterization techniques that were used.    Small organic molecules (those containing carbon, hydrogen and a handful of other elements) were generally thought to be pure if crystallized.  That’s OK for things like aspirin that are solid at room temperature and can crystallize, but not universally adequate.

In 1838, a chemist called Gerardus Johannes Mulder  conducted elemental analysis of some biological molecules including albumin[1]. He managed to establish that the weight of a molecule of egg albumin had to be in excess of 55,000 because that was the mass necessary to have one whole phosphorus atom and one whole sulfur atom per molecule.  It is, of course, not possible to have fractions of atoms in molecules.  This was larger than any molecule considered, and was quite a controversial discovery.  In the mid 1800s, hemoglobin was discovered and crystallized, also a very large molecule.

Staudinger was a German chemist who worked on a variety of chemical projects before beginning study of rubber.  He proposed the idea the substances like starch, rubber and proteins were made up of repeating units, now called monomers and joined together with strong covalent bonds[2].  Again, this was controversial because other chemists at the time believed such substances to be aggregates of small molecules, held together by weaker intermolecular forces.  One implication of Staudinger’s work was the idea that a molecule could have many different formulae and still be essentially the same thing.  For example, it is difficult to distinguish a polymer molecule with 1000 monomer units joined together from one with 1001 units.

The first identified polymers were resins, gums and biopolymers, but eventually chemists worked out how to synthesise molecules and polymers such as neoprene rubber and nylon were created and exploited for a vast array of uses.

[1] Mulder, Journal für praktische Chemie 16, 129 (1839)

[2] Staudinger http://en.wikipedia.org/wiki/Hermann_Staudinger

Coming up: classifying polymers, polymers in medicine, food and the environment, in however many parts it takes!

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