Kevlar is the DuPont brand name for an aramid (aromatic amide) polymer first developed in 1965. The para orientation of the benzene substituents in the repeating unit allows a high degree of hydrogen bonding between polymer chains in this material. As a result, the polymer in the solid phase forms rod-like liquid crystal packing structures. Spun fibers of this material are exceptionally strong; Kevlar has about eight times the strength of steel on a per-weight basis.
The synthesis and processing of Kevlar is difficult, since a solution of concentrated sulfuric acid is required to dissolve the polymer, and consequently the price for this polymer is quite high. Nevertheless, it’s unique combination of strength, low density and flexibility have led to numerous applications, including body armour, bridge cables and the roof of Montreal’s Olympic stadium.