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At Wikipedia a monomer is defined to be

a molecule that may bind chemically to other molecules to form a polymer.

A polymer is defined to be

a molecule composed of many monomers.

These definitions are obviously circular.

Are there non-circular definitions of monomers and polymers?

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  • $\begingroup$ Circular definitions for a circular concept. These seem pretty good. I might embellish the definition with "a molecule or collection of atoms (monomer) that may bind with other like molecules to make a new molecule (polymer) that is comprised of their sequence." $\endgroup$ – Eric Brown Jun 3 '14 at 19:42
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The term "monomer" only has meaning in the context of discussing polymerization.

A polymer is a molecular chain where the links of the chain are repeated identical or a least similar units. Examples where the units are idential would be polypropylene, polyvinylchloride and polysiloxane. Example where the units are similar but not necessarily identical would be DNA and proteins.

A monomer is a molecule that can react to form a single unit of a polymer.

For example, propylene is a monomer of poylpropylene and amino acids are monomers of a protein.

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Let's have a look at what IUPAC say; they would be a reliable source to get definitions of chemical terminology from:

Monomer:

"A substance composed of monomer molecules."

Monomer molecules:

"A molecule which can undergo polymerization thereby contributing constitutional units to the essential structure of a macromolecule. "

Polymer:

"A substance composed of macromolecules."

Macromolecule:

"A molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass. "

These definitions are consistent with the latest IUPAC Compendium of Polymer Terminology and Nomenclature, IUPAC Recommendations 2008

Note that, historically, the definition of a polymer has changed somewhat. Up until about 80 years ago, polymers were seen as molecules comprised of similar empirical formula - benzene, for example, was considered a polymer of acetylene. It was Staudinger's work in the 1920's (contributing to his Nobel Prize) that defined polymers as macromolecules.

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