atom from a weak C-H bond give a hydroperoxide (ROOH) and a fresh carbon-centred radical. The hydroperoxides can then undergo a number of possible homolytic reactions to generate more radicals, giving an accelerating reaction. As the concentration of radicals increases chain termination reactions become more important, these reduce the number of radicals by radical disproportionation or combination, leading to a sigmoid reaction plot. Chain initiation Polymer -> P\bullet +\ P\bullet Chain propagation P\bullet +\ O2 -> POO\bullet POO\bullet +\ PH -> {POOH} +\ P\bullet Chain branching POOH -> PO\bullet +\ OH\bullet {PH} + OH\bullet -> P\bullet +\ H2O PO\bullet -> Chain\ scission\ reactions Termination POO\bullet +\ POO\bullet -> cross\ linking\ reaction\ to\ non-radical\ product POO\bullet +\ P\bullet -> cross\ linking\ reaction\ to\ non-radical\ product P\bullet +\ P\bullet -> cross\ linking\ reaction\ to\ non-radical\ product In oils and polymers The autoxidation of unsaturated fatty acids causes them to crosslink to form polymers. This phenomenon has been known since antiquity and forms the basis of drying oils, which were traditionally used to make many varnishes and paints. Linseed oil, which is rich in polyunsaturated fats, is a prime example. Conversely, autoxidation can also cause polymers such as plastics to deteriorate. Sensitivity varies depending in the polymer backbone, in general structures containing unsaturated groups, allylic and benzylic C−H bonds and tertiary carbon centres are more susceptible, rubbers are therefore particularly sensitive. Autoxidation can be inhibited by a wide range of polymer stabilizers, or accelerated by biodegradable additives. Similarly, antioxidant oil additives and fuel additives are used to inhibit autoxidation. In food The prevention of autoxidation is important in the food and drink industry and is achieved both by both chemical preservatives and a range of oxygen excluding food preservation techniques such as canning. It is well known that fats, especially polyunsaturated fats, become rancid, even when kept at low temperatures, however many other foods are susceptible to autoxidation. The complex mixture of compounds found in wine, including polyphenols, polysaccharides, and proteins, can undergo autoxidation during the aging process, leading to wine faults. The browning of many foods, such as skinned apples, can be considered an autoxidation process, although it is generally an enzymatic process such as lipid peroxidation which proceeds via a different mechanism to the one shown above. In industry In the chemical industry many chemicals are produced by autoxidation: in the cumene process phenol and acetone are made from benzene and