Chemistry - Why is polyethylene not called polymethylene?

Solution 1:

According to the Compendium of Polymer Terminology and Nomenclature (IUPAC Recommendations 2008, i.e. the ‘Purple Book’), three different types of names can be used for polymers:

  • traditional names,
  • structure-based names, and
  • source-based names.

When traditional names fit into the general pattern of systematic nomenclature, they are retained, in this case: polyethylene (PE)

The systematic name for a polymer requires the naming of a preferred constitutional repeating unit (CRU). If necessary, this basic name is then modified by prefixes. The systematic structure-based name for polyethylene according to the Purple Book is indeed poly(methylene).

Polymers can also be named as being derived from a monomer (or precursors), which is named according to IUPAC rules. Such names are referred to as source-based names. The systematic source-based name for polyethylene according to the Purple Book is polyethene.

Solution 2:

Polyethylene is prepared by polymerizing ethylene. Ethylene has a double bond, thanks to which the polymerization goes on. You could not do that with a methylene group. So the name comes after the smallest unit which is actually used to prepare the polymer.