Polyacrylonitrile (PAN) is a synthetic, semicrystalline organic polymer resin, with the linear formula (CH₂CHCN)_n. Almost all PAN resins are copolymers with acrylonitrile as the main monomer. PAN is used to produce large variety of products including ultra filtration membranes, hollow fibers for reverse osmosis, fibers for textiles, and oxidized PAN fibers. PAN fibers are the chemical precursor of very high-quality carbon fiber. PAN is first thermally oxidized in air at 230 °C to form an oxidized PAN fiber and then carbonized above 1000 °C in inert atmosphere to make carbon fibers found in a variety of both high-tech and common daily applications such as civil and military aircraft primary and secondary structures, missiles, solid propellant rocket motors, pressure vessels, fishing rods, tennis rackets and bicycle frames. It is a component repeat unit in several important copolymers, such as styrene-acrylonitrile (SAN) and acrylonitrile butadiene styrene (ABS) plastic.

Polyacrylonitrile (PAN) was first synthesized in 1930 by Hans Fikentscher and Claus Heuck in the Ludwigshafen works of the German chemical conglomerate IG Farben. However, as PAN is non-fusible, and did not dissolve in any of the industrial solvents being used at the time, further research into the material was halted.

In 1931, Herbert Rein, head of polymer fiber chemistry at the Bitterfeld plant of IG Farben, obtained a sample of PAN while visiting the Ludwigshafen works. He found that pyridinium benzylchloride, an ionic liquid, would dissolve PAN. He spun the first fibers based on PAN in 1938, using aqueous solutions of quaternary ammonium sodium thiocyanate and aluminum perchlorate for the production process and considered other solvents including DMF. However, commercial introduction was delayed due to the wartime stresses on infrastructure, inability to melt the polymer without degradation, and solvents to allow solution processing were not known yet.

The first mass production run of PAN fiber was in 1946 by American chemical conglomerate DuPont. The German intellectual property had been stolen in Operation Paperclip. The product, branded as Orlon, was based on a patent filed exactly seven days after a nearly identical German claim. ^{[failed verification]}

In the German Democratic Republic (GDR), industrial polyacrylonitrile fibre production was started in 1956 at the VEB Film- und Chemiefaserwerk Agfa Wolfen due to the preliminary work of the "Wolcrylon" collective (de:Max Duch, Herbert Lehnert et al.). Prior to this, the preconditions for the production of the raw materials had been created at the Buna Werke Schkopau (Polyacrylonitrile) and Leuna works (Dimethylformamide). In the same year, the collective was awarded the GDR's National Prize II Class for Science and Technology for its achievements.

Although it is thermoplastic, polyacrylonitrile does not melt under normal conditions. It degrades before melting. It melts above 300 °C if the heating rates are 50 degrees per minute or above.

Glass transition temperature is around 95 °C and fusion temperature is at 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. Solubility parameters: 26.09 MPa^1/2 (25 °C) are 25.6 to 31.5 J^1/2 cm^−3/2. Dielectric constants: 5.5 (1 kHz, 25 °C), 4.2 (1 MHz, 25 °C).Can behave as branched as well as linear polymer.

In the production of carbon fibers containing 600 tex (6k) PAN tow, the linear density of filaments is 0.12 tex and the filament diameter is 11.6 μm which produces a carbon fiber that has the filament strength of 417 kgf/mm2 and binder content of 38.6%.