# Why is polyethylene not called polymethylene?

I understand that the monomer that polymerises to give polyethylene is an ethylene, but after polymerisation, the smallest repeating monomer in polyethylene seems to be a methyl and not an ethyl. So why don’t we call it polymethylene instead?

• Because methylene is not a compound in its own right. Who said we must name the polymer after the smallest repeating unit? Jun 29, 2018 at 7:15
• Well that’s what my polymers professor said, and that seems to be the trend for all other polymers (as far as I have learned).
– P...
Jun 29, 2018 at 7:16
• For all other polymers, the smallest repeating unit is the same as the molecule that was polymerized. For polyethylene it is different. Jun 29, 2018 at 7:19
• @IvanNeretin it is, actually, a compound in its own right, albeit a radical and thus hard to handle. Jun 29, 2018 at 14:07
• @IvanNeretin "Who said we must name the polymer after the smallest repeating unit?" – The IUPAC Recommendations 2008 said that.
– user7951
Jun 29, 2018 at 15:35

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:

• Although this certainly is the reason, I have to remark that it's a bit weird to name a compound after how it's synthesized in practice. Who's to say that a better process isn't developed in the future that will start from, say, hex-1-ene? Surely the product shouldn't suddendly be renamed to polyhexylene, if it has the same chemical structure as polyethylene. And although I reckon it will never be feasible to polymerise this from $\mathrm{CH_2}$, it's certainly conceivable. Jun 29, 2018 at 14:04