= Polyglycolic acid
{wiki=Polyglycolide}
= Polyglycolide
{synonym}
\b[Polyglycolic acid], also called <polyglycolide>, is a <polyester> whose backbone contains the <repeat unit>
$$
\left[-\mathrm O-\mathrm{CH}_2-\mathrm C(=\mathrm O)-\right]_n.
$$
The repeated <ester> connections make <hydrolysis> chemically different from merely dissolving an unchanged chain. The manufacturer's technical brochure identifies the structure and distinguishes hydrolytic decomposition to <glycolic acid> from subsequent microbial degradation.<Kuredux Polyglycolic Acid Resin technical brochure by Kureha>[March 2022 brochure, PDF p. 2, Molecular Structure and decomposition diagram]{ref}
The repeat unit has composition $\mathrm{C_2H_2O_2}$ and approximate <molar mass> $58.04\,\mathrm{g\,mol^{-1}}$. An original ideal linear chain with hydroxyl and carboxyl ends has molar mass approximately
$$
M\simeq58.04n+18.02\quad\mathrm{g\,mol^{-1}},
$$
where the final term accounts for the combined end-group contribution in this specified chain structure. At <degree of polymerization> $n=1000$, this gives about $58.06\,\mathrm{kg\,mol^{-1}}$. A real sample contains a distribution of chain lengths and may have different end groups; its <number-average molar mass> is not fixed by the material name alone.
<Ester hydrolysis> cuts a chain into shorter molecules. In an original counting example, ten distinct backbone cuts in a single linear chain of 1000 repeat units produce eleven fragments with mean $1000/11\approx90.9$ repeat units per fragment, assuming no units are lost. The large change in mean chain length can occur before fragments leave the specimen. <Polyglycolic-acid chain scission and mass loss> therefore need separate measurements.
A useful physical experiment exposes specimens to controlled water conditions, then compares molecular-mass information, retained dry mass and mechanical response. The manufacturer's hydrolyzability test measures filtered, dried residue after timed water exposure at specified temperatures.<Kuredux Polyglycolic Acid Resin technical brochure by Kureha>[PDF p. 3, Degradability test method and temperature-labelled curves]{ref} That residue measures retained material, not directly the number of broken backbone bonds. A specimen can lose load-bearing chain connectivity before all fragments become soluble or escape.
Temperature, specimen geometry and exposure conditions belong with a degradation result. A trade-name test curve is evidence for the tested material and protocol, not a universal disappearance time for every <polyglycolic acid> article. The combination of a chemically identifiable backbone and experimentally variable degradation makes the polymer useful for studying how molecular changes become material-scale property changes.
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