Polymeroxidation

Polymer oxidation is a degradation process that affects polymers, leading to changes in their physical and chemical properties. This process is typically initiated by the interaction of polymer chains with oxygen, often in the presence of heat, light, or mechanical stress. The reaction proceeds through a free radical chain mechanism.

The initial step involves the formation of free radicals on the polymer backbone, often due to homolytic cleavage of weak chemical bonds. These polymer radicals then react with oxygen to form peroxy radicals. Peroxy radicals can abstract hydrogen atoms from other polymer chains, propagating the radical chain and forming hydroperoxides. Hydroperoxides are unstable and can decompose into highly reactive alkoxy and hydroxyl radicals.

These newly formed radicals can then initiate further oxidation reactions, leading to chain scission (breaking of polymer chains) or cross-linking (formation of new bonds between polymer chains). Chain scission generally results in a decrease in molecular weight, leading to reduced mechanical strength, embrittlement, and loss of elasticity. Cross-linking, on the other hand, can increase the rigidity and brittleness of the polymer.

Polymer oxidation can lead to visible changes such as discoloration, surface cracking, and changes in gloss. The rate and extent of oxidation depend on the specific polymer type, its molecular structure, the presence of impurities or additives, and the environmental conditions. For example, polymers with unsaturated bonds or tertiary carbon atoms in their backbone are generally more susceptible to oxidation. Stabilizers, such as antioxidants, are often added to polymers to inhibit or slow down the oxidation process and extend their service life.