= Polyester
A \b[polyester] is a <polymer> whose <polymer backbone> contains carboxylic <ester> linkages. The location of the linkage matters: a polymer carrying ester groups only as side groups is excluded from this structural class by the IUPAC definition.<Polyester in the IUPAC Gold Book>[entry 15278, definition and note 4; original glossary, printed p. 1154]{ref}
<Polyglycolic acid> gives a compact backbone example:
$$
\left[-\mathrm O-\mathrm{CH}_2-\mathrm C(=\mathrm O)-\right]_n.
$$
Following the main chain passes through the ester oxygen and carbonyl connection. The manufacturer's structural diagram identifies this polyester repeat unit.<Kuredux Polyglycolic Acid Resin technical brochure by Kureha>[March 2022 brochure, PDF p. 2, Molecular Structure]{ref} In <polyvinyl acetate>, by contrast, the carbon–carbon backbone carries acetate side groups. Those groups can be chemically transformed without making every backbone connection an ester.
<Polycondensation> of suitable multifunctional monomers is one route to a polyester. An original ideal <step-growth polymerization> count explains why high conversion matters. Start with $N_0$ bifunctional molecules, allow only intermolecular bond-forming reactions, and exclude rings, branching and unequal functional-group stoichiometry. Each new connection reduces the number of separate molecules by one. If a fraction $p$ of the initial functional groups has reacted, the number of connections is $pN_0$, so
$$
N=N_0(1-p),\qquad X_n=\frac{N_0}{N}=\frac1{1-p}.
$$
Conversions 0.99 and 0.999 give number-average <degree of polymerization> values 100 and 1000 in this stipulated model. Unequal functionality, end-group imbalance and ring formation change the calculation. The equation is a mechanism model, not a guarantee for an actual synthesis.
<Ester hydrolysis> can cut a polyester backbone, linking chemical transformation to changing chain length and material properties. Hydrolysis of a side-chain ester need not cut the carbon–carbon backbone of the contrasting example. “Contains an ester” and “is a polyester” therefore predict different possible consequences of the same reaction type.
A structural class alone does not specify modulus, degradation rate or processing behaviour. Backbone groups, chain-length distribution, morphology and exposure conditions all matter. Measure the relevant <molar mass> and physical response rather than transferring a numerical property from one polyester solely because the class name agrees.
Back to article page
