Polyacrylonitrile
Synthetic polymer precursor for carbon fiber and acrylic textiles.
Polyacrylonitrile (PAN) is a synthetic, semicrystalline organic polymer resin with the linear formula (CH2CHCN)n. Nearly all PAN resins are copolymers where acrylonitrile serves as the primary monomer. This material goes into a wide range of products, such as ultrafiltration membranes, hollow fibers for reverse osmosis, textile fibers, and oxidized PAN fibers. PAN fibers also serve as the chemical precursor for high-quality carbon fiber, and PAN itself is a repeating unit in important copolymers like styrene-acrylonitrile (SAN) and acrylonitrile butadiene styrene (ABS) plastic.
The first synthesis of PAN occurred in 1930 by Hans Fikentscher and Claus Heuck at IG Farben’s Ludwigshafen plant. Research stalled because PAN does not melt and could not be dissolved in any industrial solvents available at the time. In 1931, Herbert Rein, head of polymer fiber chemistry at IG Farben’s Bitterfeld plant, obtained a PAN sample during a visit to Ludwigshafen. He discovered that pyridinium benzylchloride, an ionic liquid, could dissolve PAN. By 1938, he had spun the first PAN fibers using aqueous solutions of quaternary ammonium sodium thiocyanate and aluminum perchlorate, and he also considered other solvents like DMF. Commercial production was delayed due to wartime infrastructure strains, the polymer’s inability to melt without degrading, and the lack of known solvents for solution processing. The first mass production of PAN fiber began in 1946 by the American company DuPont, using intellectual property taken from Germany during Operation Paperclip. The product, branded Orlon, was based on a patent filed exactly seven days after a nearly identical German claim. In the German Democratic Republic, industrial PAN fiber production started in 1956 at VEB Film- und Chemiefaserwerk Agfa Wolfen, building on work by the “Wolcrylon” collective (including Max Duch and Herbert Lehnert). Raw material production had been set up earlier at Buna Werke Schkopau (for polyacrylonitrile) and Leuna works (for dimethylformamide). That same year, the collective received the GDR’s National Prize II Class for Science and Technology.
Though thermoplastic, PAN does not melt under normal conditions; it degrades before melting. It will melt above 300 °C if heated at rates of 50 degrees per minute or faster. Its glass transition temperature is around 95 °C, and its fusion temperature is 322 °C. PAN dissolves in polar solvents such as dimethylformamide, dimethylacetamide, ethylene and propylene carbonates, and in aqueous solutions of sodium thiocyanate, zinc chloride, or nitric acid. Its solubility parameters at 25 °C are 25.6 to 31.5 J¹/² cm⁻³/², and its dielectric constants are 5.5 at 1 kHz and 4.2 at 1 MHz (both at 25 °C). The polymer can behave as either branched or linear. In the production of carbon fibers from a 600 tex (6k) PAN tow, the linear density of individual filaments is 0.12 tex, the filament diameter is 11.6 μm, the resulting carbon fiber has a filament strength of 417 kgf/mm², and the binder content is 38.6%.
Most commercial synthesis of PAN uses free radical polymerization of acrylonitrile. Typically, 1–10% of other vinyl comonomers are added, depending on the final application. Common comonomers include acrylic acid, acrylamide, allyl compounds, and sulfonated styrene. Anionic polymerization can also be used. For textile applications, molecular weights range from 40,000 to 70,000; for carbon fiber production, higher molecular weights are preferred.
Homopolymers of PAN are used in hot gas filtration systems, outdoor awnings, yacht sails, and fiber-reinforced concrete. Copolymers containing PAN are often made into fibers for knitted clothing such as socks and sweaters, as well as outdoor items like tents. If a clothing label says “acrylic,” the material is a copolymer of polyacrylonitrile. DuPont first spun PAN into fiber in 1942, marketing it as Orlon. Acrylonitrile is also a common comonomer with styrene in plastics like acrylonitrile, styrene, and acrylate blends. Labeling a garment as “acrylic” means the polymer contains at least 85% acrylonitrile monomer. A typical comonomer is vinyl acetate, which allows the fibers to soften enough for dye penetration. Acrylic fibers are low-cost compared to natural fibers, offer better sunlight resistance, and resist moth damage. Halogen-containing comonomers produce modacrylics, which contain 35–85% PAN. The halogen groups improve flame resistance, making modacrylics suitable for sleepwear, tents, and blankets. Some mattresses also use them to meet North American flame resistance requirements. However, modacrylics are costly and can shrink after drying. PAN also absorbs many metal ions, making it useful in absorption materials.
- first_synthesized_by
- Hans Fikentscher and Claus Heuck
- first_mass_producer
- DuPont
- glass_transition_temperature
- ~95 °C
- common_uses
- carbon fiber precursor, textiles, filtration membranes
Lore & Background
Polyacrylonitrile (PAN) is a synthetic, semicrystalline organic polymer resin with the linear formula (CH₂CHCN)ₙ. In its pure form, the polymer does not melt under normal conditions and degrades before reaching a melting point, though it can melt above 300 °C if heated rapidly at rates of 50 °C per minute or more. Its glass transition temperature is approximately 95 °C, and its fusion temperature is 322 °C. PAN is soluble in polar solvents such as dimethylformamide, dimethylacetamide, ethylene and propylene carbonates, and in aqueous solutions of sodium thiocyanate, zinc chloride, or nitric acid. It can behave as either a branched or linear polymer. The material is almost always used as a copolymer with acrylonitrile as the main monomer, and common comonomers include acrylic acid, acrylamide, allyl compounds, and sulfonated styrene. PAN fibers serve as the chemical precursor for very high-quality carbon fiber: they are first thermally oxidized in air at 230 °C to form oxidized PAN fiber, then carbonized above 1000 °C in an inert atmosphere. These carbon fibers are employed in civil and military aircraft structures, missiles, solid propellant rocket motors, pressure vessels, fishing rods, tennis rackets, and bicycle frames. PAN also appears as a component in copolymers such as styrene-acrylonitrile (SAN) and acrylonitrile butadiene styrene (ABS) plastic.
Reader's Guide
Polyacrylonitrile is significant primarily as the precursor for 90% of carbon fiber production, a material essential to modern aerospace and high-performance composites. Approximately 20–25% of Boeing and Airbus wide-body airframes are carbon fibers derived from PAN. Its high tensile strength and modulus of elasticity, established by fiber sizing, coatings, and production processes, make it critical in composite structures for military and commercial aircraft. Beyond carbon fiber, PAN is used in ultrafiltration membranes, hollow fibers for reverse osmosis, and textiles. Acrylic fibers, which consist of at least 85% acrylonitrile, are low-cost alternatives to natural fibers with better sunlight resistance and resistance to moths. Modacrylics, containing halogen comonomers, offer flame resistance for sleepwear, tents, and blankets. PAN also serves as a support polymer for ion exchange resins; divinylbenzene-crosslinked PAN is a precursor to weakly acidic resins with high affinities for divalent metal ions. Despite its utility, applications are limited by PAN's high price of around $15/lb. Its legacy includes enabling lightweight, strong materials for both high-tech and everyday products, from aircraft to fishing rods.
Did You Know?
- PAN is the precursor for 90% of carbon fiber production.
Position Among Synthetic Polymers
Polyacrylonitrile occupies a notable position in the hierarchy of synthetic polymers ranked by worldwide demand. It appears in the list alongside polyethylene, polypropylene, polystyrene, polyvinyl chloride, synthetic rubber, phenol formaldehyde resin, neoprene, nylon, PVB, and silicone. Like most synthetic polymers used for plastics, polyacrylonitrile's continuously linked backbone consists mainly of carbon atoms, distinguishing it from materials where silicon or oxygen form the primary structural framework. As a synthetic polymer, it stands in contrast to naturally occurring materials such as hemp, shellac, amber, wool, silk, natural rubber, and cellulose, which have served human needs for centuries. The broad spectrum of properties that synthetic polymers like polyacrylonitrile offer has made them essential and ubiquitous in everyday life, filling roles that natural materials alone could not satisfy.
The Chemistry of Its Formation
The creation of polyacrylonitrile falls within the broader process of polymerization, in which many small molecules called monomers are combined into a covalently bonded chain or network. During this process, certain chemical groups may be lost from each monomer, as seen in other polymerizations where water molecules are eliminated. The distinct fragment of each monomer that becomes incorporated into the final polymer is termed a repeat unit or monomer residue. Synthetic polymerization methods are generally divided into two principal categories: chain polymerization, where monomers are added to a growing chain one at a time, and step-growth polymerization, where chains of monomers may combine directly with one another. The latter can be further subdivided into polycondensation, which produces a low-molar-mass by-product at each reaction step, and polyaddition. These reactions may proceed with or without a catalyst, and newer techniques such as plasma polymerization do not fit neatly into either traditional category.
Structural Characteristics and Physical Properties
As a polymer, polyacrylonitrile inherits a set of physical properties that emerge from its large molecular mass relative to small-molecule compounds. These properties include toughness, high elasticity, viscoelasticity, and a characteristic tendency to form amorphous and semicrystalline structures rather than true crystals. The structure of any polymeric material, including polyacrylonitrile, can be described across a hierarchy of length scales, ranging from the sub-nanometer level up to the macroscopic. Each structural stage provides the foundation for the next, creating a nested architecture that ultimately determines the material's behavior. This structural complexity is what allows polymers to serve such diverse applications. The study of these properties falls within polymer science, encompassing both polymer chemistry and polymer physics, as well as materials science and engineering. The broad spectrum of properties available in synthetic polymers like polyacrylonitrile is precisely what makes them essential and ubiquitous in everyday life.
Intellectual Heritage and Scientific Context
The very concept of what polyacrylonitrile is—a macromolecular structure built from repeating subunits—rests on intellectual foundations laid over nearly a century. The term 'polymer' itself derives from the Greek words polus, meaning many or much, and meros, meaning part. Today, the science surrounding materials like polyacrylonitrile is pursued across multiple disciplines, including polymer chemistry, polymer physics, biophysics, and materials science and engineering. Historically, the primary focus has been on products arising from the linkage of repeating units by covalent chemical bonds, though an emerging area now examines supramolecular polymers formed by non-covalent links, broadening the field's scope considerably.
Frequently Asked Questions
Who is Polyacrylonitrile?
PAN is a synthetic, semicrystalline linear polymer built from repeating acrylonitrile units (CH2CHCN)n, and in practice it is almost always a copolymer with acrylonitrile as the dominant monomer. Hans Fikentscher and Claus Heuck first synthesized it, while DuPont became the first company to bring it to commercial-scale production.
What are Polyacrylonitrile's powers or main roles?
PAN's headline job is acting as the chemical precursor for high-quality carbon fiber, but it also appears in ultrafiltration membranes, reverse-osmosis hollow fibers, and textile fibers. It additionally shows up as a repeat-unit component in widely used copolymers such as SAN and ABS plastic.
How does Polyacrylonitrile's story end?
When PAN fibers are thermally oxidized and then carbonized, the nitrile groups rearrange into a turbostratic carbon lattice, effectively transforming the polymer into carbon fiber. In membrane or textile applications, the material simply serves until it is eventually replaced or recycled.
Why is Polyacrylonitrile important?
Without PAN as a precursor, producing high-strength, high-modulus carbon fiber at industrial scale would be far more difficult, which is why it underpins aerospace, automotive, and sporting-goods sectors. Its versatility across filtration, textiles, and copolymer chemistry makes it one of the most industrially consequential nitrile-based polymers.
What is Polyacrylonitrile's glass transition temperature?
PAN shifts from a rigid glassy state to a rubbery one at roughly 95 °C, a value that directly governs how the fiber is processed and stabilized during carbonization. This relatively high Tg helps the fiber retain its shape well through the oxidation stage.
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