= Polyethylene terephthalate
{title2=$(\mathrm{C}_{10}\mathrm{H}_8\mathrm{O}_4)_n$}
{wiki}
= PET polymer
{c}
{synonym}
\b[Polyethylene terephthalate], more explicitly poly(ethylene terephthalate), is a <polyester> made from ethylene-glycol and terephthalate-derived units. It is often called <PET polymer> in materials contexts. Its chain contains repeated ester connections and para-substituted aromatic rings; it is not <polyethylene> with a physically mixed additive. ACS identifies the material as a condensation polymer of <ethylene glycol> and <terephthalic acid>.<Poly(ethylene terephthalate) by American Chemical Society>[Molecule of the Week, 17 October 2022, structural description]{ref}
An ideal repeat can be written
$$
\left[-\mathrm O-\mathrm{CH}_2-\mathrm{CH}_2-\mathrm O-\mathrm C(=\mathrm O)-\mathrm{C}_6\mathrm H_4-\mathrm C(=\mathrm O)-\right]_n,
$$
with the two aromatic attachments opposite one another. Counting this repeat gives $\mathrm{C_{10}H_8O_4}$. The same count follows from the monomer formulas:
$$
\mathrm{C_2H_6O_2}+\mathrm{C_8H_6O_4}-2\mathrm{H_2O}=\mathrm{C_{10}H_8O_4}.
$$
This is repeat-unit bookkeeping; exact finite-chain composition also includes the end groups.
Using standard rounded atomic masses, the repeat contributes about $192.17\,\mathrm{g\,mol^{-1}}$. An original ideal chain with 1000 such repeats therefore has about $192.17\,\mathrm{kg\,mol^{-1}}$ of repeat-unit mass before end-group corrections. A real sample has a <molar mass distribution>; the repeat count does not assign one molecular mass to every chain.
The ester connections are part of the <polymer backbone>. Their cleavage by <hydrolysis> can shorten chains before all products leave the specimen, so retained mass and <number-average molar mass> need separate observations. <Polymer fraction-recovery balance> is relevant when soluble fragments and retained material are sampled differently. Neither the polyester label nor a bottle's disappearance from view identifies a degradation mechanism.
An illustrative comparison takes two samples with identical repeat chemistry but different crystallization and processing histories. Their thermal and mechanical responses can differ without a change in the repeat formula. A proposed experiment compares thermal response and chain-distribution measurements under documented conditioning, while checking for hydrolytic change during preparation. This separates molecular identity, chain length and material organization. The derivations here describe an ideal structure; no universal processing temperature or degradation rate is inferred from it.
Back to article page
