Polyethylene (PE) plastics comprise high density PE, low density PE, cross-linked PE (PEX), linear PE, low density and high density linear PE, etc. Are these all considered polymorphs, or is there another name for them? (Polymorphism refers to crystal structure, so I'm thinking the various forms of polyethylene probably aren't polymorphs.)

I guess a more general form of this question is: what is the name for the same basic chemical (polyethylene, in this case) that can form different compounds with different properties based on how the basic molecule branches (isomer doesn't quite seem to fit, either)?

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    $\begingroup$ I wouldn't even call them different compounds. See, there is no strict border between them; this, IMHO, is more important than the difference in properties. $\endgroup$ Feb 15, 2017 at 21:27
  • $\begingroup$ Yeah, agreed. But I couldn't think of another term, but each of the different forms of polyethylene have different densities, melting points, etc. $\endgroup$
    – BillDOe
    Feb 15, 2017 at 21:28
  • $\begingroup$ @IvanNeretin, is the term allotrophs maybe more appropriate? $\endgroup$
    – airhuff
    Feb 15, 2017 at 22:17
  • $\begingroup$ I think I'd personally just say different types of polyethylene. Allotropy refers to a pure element, so probably doesn't work here. $\endgroup$ Feb 15, 2017 at 22:22
  • $\begingroup$ Polymer? But I thought that just refers to long-chain molecules like polyethylene, polytetrafluoroethylene, polychloroprene, etc. $\endgroup$
    – BillDOe
    Feb 15, 2017 at 23:56


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