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Terylene is a polyester made from terephthallic acid and ethylene glycol. Even though we use two reagents, they undergo esterification to give bis(2-hydroxyethyl) terephthalate (monomer) which then undergo polymerization.

So, is it correct to consider terylene as a copolymer? My reasoning tells that it should be a homopolymer. Same line of reasoning gives nylon, phenol-formaldehyde resin, bakelite — all as homopolymer.

But majority of questions which I go through considered the above polymers as copolymers. What is correct? Are they homopolymers or copolymers?

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  • $\begingroup$ Whatever we decide to be correct is OK. This is a human convention, not a fact of nature. $\endgroup$
    – Ivan Neretin
    Feb 5 '20 at 7:16
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    $\begingroup$ It is not a requirement to be monomer ester to prolong the polymer chain. The EG can attach itself to the polymer carboxy end, the acid to alkoholic end. But better then copolymer is copolycondensate, as water is eliminated. $\endgroup$
    – Poutnik
    Feb 5 '20 at 7:56
  • $\begingroup$ It's not a copolymer and common name is PET not some "terylene". $\endgroup$
    – Mithoron
    Feb 5 '20 at 17:55
  • $\begingroup$ Is terylene brand name for PET $\endgroup$
    – Grace
    Feb 5 '20 at 17:57
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    $\begingroup$ PET = PolyEthyleneTerephthalate = polyester of terephthalic acid and ethylenglykol. So yes, If terylene is what you say it is, then it is the brand name for PET. $\endgroup$
    – Poutnik
    Feb 6 '20 at 8:14
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No, PET it is definitely not a copolymer. Neither is e.g. Nylon 6,11 (or any other polyamide with two numbers). The monomers alone would not polymerise, or at least only by a very different reaction (e.g. ethylene gylcol gives PEG).

What you can have are alternating copolymers, but there the sequence is a statistical property. It comes when a reactive chain end B* has a higher probability to add an A (to give BA*), and a chain end A* to add B (to give AB*). That probability is sensitive to monomer composition, the temperature, pressure, catalyst, etc. If you want to read more about that, "copolymerisation parameters" is the topic to look up. The monomers you see there are afaik invariably olefines, i.e. they have a double bond that undergoes polymerisation.

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