Polyester
A versatile polymer family used in textiles, bottles, and engineering.
Wikifrits · CC0
Polyester is a broad family of polymers defined by having one or two ester links in each repeat unit of their main chain. The most common type is polyethylene terephthalate (PET). While some polyesters occur naturally—for instance, in plants and insects—and a few synthetic versions are biodegradable, the vast majority of commercial polyesters are not. They are widely used in clothing.
Synthetic polyester fibers are often blended with natural fibers to create fabrics with combined advantages. Cotton-polyester blends, for example, are strong, resist wrinkles and tearing, and shrink less. Compared to plant-derived fibers, polyester fibers offer high resistance to water, wind, and environmental conditions, though they are less fire-resistant and can melt if ignited. Liquid crystalline polyesters were among the first liquid crystal polymers used industrially, valued for their mechanical strength and heat resistance; these properties also make them useful as abradable seals in jet engines.
Polyesters can be divided by structure. Those with one ester linkage per repeat unit include polyhydroxyalkanoates like polylactic acid, while those with two ester linkages per repeat unit include PET. Economically, polyesters are among the most important polymer classes, driven largely by PET, a commodity plastic of which about 30.5 million metric tons were produced worldwide in 2019. The family’s properties vary widely depending on the R group in the polymer chain.
Natural polyesters include cutin, a component of plant cuticles made from omega hydroxy acids linked by ester bonds into polymers of indefinite size. Some bees in the genus *Colletes* also produce a polyester lining for their underground brood cells, earning them the nickname “polyester bees.”
Synthetic polyesters cover many types. Linear aliphatic high-molecular-weight polyesters (Mn >10,000) are low-melting semicrystalline polymers (melting point 40–80 °C) with poor mechanical properties. Their hydrolytic instability makes them biodegradable, suitable for packaging, disposable items, agricultural mulch films, and biomedical uses. Lower-molecular-weight aliphatic hydroxy-terminated polyesters (Mn <10,000) serve as macromonomers for polyurethanes. Hyperbranched polyesters, with low viscosity and high solubility, are used as rheology modifiers in thermoplastics or crosslinkers in coatings. Aliphatic–aromatic polyesters—such as PET, PBT, PHT, and PTT (Sorona)—are high-melting semicrystalline materials (melting point 160–280 °C) used in engineering thermoplastics, fibers, and films. Wholly aromatic linear copolyesters offer superior mechanical properties and heat resistance for high-performance applications. Unsaturated polyesters, made from multifunctional alcohols and unsaturated dibasic acids, are cross-linked and used as matrices in composites; alkyd resins, from polyfunctional alcohols and fatty acids, cross-link in air and are common in coatings and composites. Thermoplastic polyester elastomers (TPEE) are rubber-like. Unsaturated polyester resins (UPR) are thermosetting, used as casting materials, in sheet molding compounds, fiberglass laminating resins, and non-metallic auto-body fillers, as well as in pre-pregs. Fiberglass-reinforced UPR is common in yacht hulls and car body parts. Depending on chemistry, polyester can be thermoplastic or thermoset; most common types are thermoplastics. Two-component systems react hydroxyl groups with isocyanates to form pigmented coatings. Thermoplastic polyesters can change shape with heat; while combustible at high temperatures, they tend to shrink from flames and self-extinguish. Polyester fibers have high tenacity and modulus, low water absorption, and minimal shrinkage. Increasing aromatic content raises glass transition temperature, melting point, thermostability, chemical stability, and solvent resistance. Telechelic oligomers like polycaprolactone diol (PCL) and polyethylene adipate diol (PEA) are used as prepolymers.
In terms of thermal performance, polymers with high aromatic content are often called high-performance plastics, with continuous service temperatures above 150 °C. Engineering plastics (e.g., polyamide, polycarbonate) retain properties above 100 °C, while commodity plastics (e.g., polyethylene, polypropylene) have greater limitations but are produced in large volumes at low cost. Poly(ester imides) contain aromatic structures.
- field
- Polymer chemistry and materials science
- known_for
- Widely used synthetic fiber and plastic, especially PET
- types
- Includes natural polyesters (e.g., cutin, bee secretions) and synthetic polyesters (e.g., PET, PBT, unsaturated polyesters)
- key_property
- High water, wind, and environmental resistance; less fire-resistant; can melt when ignited
Lore & Background
Polyesters occur naturally in the cutin component of plant cuticles and in secretions of bees in the genus Colletes, which line their underground brood cells with a cellophane-like polyester. Synthetic polyesters include linear aliphatic high molecular weight types that are low-melting and biodegradable, as well as aliphatic–aromatic polyesters like PET and PBT, which are high-melting semicrystalline materials used in fibers, films, and engineering thermoplastics. Wholly aromatic linear copolyesters offer superior mechanical properties and heat resistance, and liquid crystalline polyesters are among the first industrially used liquid crystal polymers, applied as abradable seals in jet engines.
Reader's Guide
They are used extensively in clothing, home furnishings, industrial fibers, bottles, films, and coatings. Cotton-polyester blends combine strength, wrinkle resistance, and reduced shrinking. Polyester fibers have high tenacity and E-modulus, low water absorption, and minimal shrinkage. While combustible at high temperatures, polyesters tend to shrink away from flames and self-extinguish upon ignition. Increasing the aromatic parts of polyesters raises their glass transition temperature, melting temperature, thermostability, chemical stability, and solvent resistance. Unsaturated polyesters are thermosetting resins used in composite materials, fiberglass laminates, and auto-body fillers. Polyesters as thermoplastics may change shape after heat application.
Did You Know?
- Polyesters include natural products such as cutin from plant cuticles and secretions from 'polyester bees' (genus Colletes).
- Most commercial polyesters are not biodegradable, though natural polyesters and a few synthetic ones are.
- Liquid crystalline polyesters are used as abradable seals in jet engines.
- Polyester fabrics are highly stain-resistant because polyester is hydrophobic and has difficulty absorbing liquids.
Chemical Architecture & Structural Diversity
Polyester is not a single compound but a broad family of polymers unified by one defining feature: the presence of one or two ester linkages within each repeating unit along the main chain. This seemingly simple structural rule opens the door to an extraordinary range of materials. The identity of the R group attached to the ester bond can be varied, producing polyesters with wildly different thermal, mechanical, and chemical behaviors. The family also spans thermoplastics that soften and reshape under heat, thermosets that cross-link permanently, hyperbranched architectures with exceptionally low viscosity, and unsaturated resins designed to cure into rigid composites. This structural versatility is what allows polyester to occupy roles as diverse as disposable packaging, jet-engine seals, and high-performance engineering plastics.
Natural Origins & Environmental Fate
Long before chemists synthesized the first polyester in a laboratory, nature had already been producing these polymers. The cutin that forms the waxy cuticle on plant surfaces is built from omega hydroxy acids and their derivatives, linked together through ester bonds into chains of indeterminate length. In the insect world, certain ground-nesting bees of the genus Colletes secrete a cellophane-like polyester lining inside their underground brood cells, earning them the colorful nickname "polyester bees." Beyond these biological examples, a meaningful subset of polyesters—both natural and some synthetic varieties—are biodegradable. Linear aliphatic high-molecular-weight polyesters, for instance, are inherently susceptible to hydrolytic breakdown, a trait that makes them attractive for environmentally sensitive uses such as disposable packaging, agricultural mulch films, and biomedical or pharmaceutical applications where a material is expected to degrade safely after serving its purpose.
Industrial Scale & Everyday Ubiquity
Few polymer families rival polyester in sheer economic weight. That volume underpins polyester's dominance in the textile industry, where it is woven or knitted into clothing on a massive scale. Designers frequently blend polyester fibers with cotton to create fabrics that combine the breathability of natural fiber with the strength, wrinkle resistance, tear resistance, and reduced shrinkage that synthetic polyester contributes. The material's utility extends far beyond apparel, however. Liquid crystalline polyesters were among the earliest liquid crystal polymers to see industrial use, valued for their outstanding mechanical strength and heat resistance. One notable application is as an abradable seal material inside jet engines, where the combination of durability and thermal tolerance is critical to safe operation.
Performance Traits & High-Performance Applications
Polyester fibers deliver a distinctive performance profile that sets them apart from plant-derived alternatives. They exhibit high tenacity and a high elastic modulus, absorb very little water, and show minimal shrinkage, making them exceptionally resistant to moisture, wind, and general environmental wear. Their fire behavior, however, is a double-edged sword: while polyester tends to shrink away from flames and self-extinguish rather than sustain a burn, it can melt when ignited, making it less fire-resistant than many natural fibers. At the high-performance end of the spectrum, wholly aromatic linear copolyesters offer superior mechanical properties and heat resistance that qualify them for demanding engineering applications. Unsaturated polyester resins, once cross-linked, serve as matrices in composite materials, fiberglass-reinforced structures for yacht hulls, automotive body panels, and pre-preg layups. Alkyd resins, a related cross-linkable family, remain a workhorse in the coatings industry.
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