Autoxidation

Autoxidation (sometimes auto-oxidation) refers to oxidations brought about by reactions with oxygen at normal temperatures, without the intervention of flame or electric spark.

[5] Typically, an induction period is seen at the start where there is little activity; this is followed by a gradually accelerating take-up of oxygen, giving an autocatalytic reaction which can only be kept in check by the use of antioxidants.

In these cases the term 'autoxidation' is often used more broadly to include spontaneous reactions with oxygen at elevated temperatures, such as in the Cumene process.

The free radical chain reaction is sometimes referred to as the Bolland-Gee mechanism[6][7] or the basic autoxidation scheme (BAS)[8] and was originally based on the oxidation of rubbers,[9] but remains generally accurate for many materials.

[11] The autoxidation of unsaturated compounds may be initiated by reactions with singlet oxygen[12] or environmental pollutants such as ozone and NO2.

[13] Saturated polymers, such as polyolefins would be expected to resist autoxidation, however in practise they contain hydroperoxides formed by thermal oxidation during their high temperature moulding and casting, which can act as initiators.

All of these processes lead to the generation of carbon centred radicals on the polymer chain (R•), typically by abstraction of H from labile C-H bonds.

This in turn abstracts an H atom from a weak C-H bond give a hydroperoxide (ROOH) and a fresh carbon-centred radical.