Stabilisation of polyacrylonitrile by oxidative transformation

The changes occurring during the heat treatment of polyacrylonitrile polymers in the presence of air up to 350 °C have been examined using both physical and chemical techniques. It is concluded that substantial oxidation does not occur until the polymer has been converted to a ladder structure containing readily oxidisable methylene groups. The development of the highly characteristic physical behaviour of the oxidised polymer, notably absence of melting and hydrophilicity, is associated with the formation of a strongly hydrogen bonded polydihydropyrid-4-one structure which acts as an internal restraint to molecular motion and permits the orientation of the parent polymer to be carried through to the higher temperature pyrolysed carbon fibre.