Oxidative degradation:
Oxidative degradation usually leads to hardening, discoloration as well as surface changes. The case of oxidative degradation of the polymer depends primarily on its structure. Thus unsaturated polymer such as polyisoprene or polybutadine containing double bonds are easily attacked by oxygen.
Mechanism of Oxidative Degradation:
The early stage of oxidative degradation is the formation of free radical sites on the chain of backbone by the attack of molecular oxygen, ozone or some free radical produced by thermal decomposition of some additives.
Where, P represents the polymer chain. Once free radical sites are formed, attack by oxygen becomes easier. Oxygen, because of its biradical nature, adds on at the free-radical site, forming a per-oxide radical.
The peroxy-radical can now attack the neighbouring segment, abstract hydrogen & form a hydro-peroxide & a new free radical site.
The hydro-peroxide formed can lead to the formation of several new free-radical sites:
With so many free radicals formed, their recombination can occur & result in the termination of the chain reactions.
Oxidation of Phenol formaldehyde:
The structure of phenol formaldehyde-
it is observed that attacks by the oxygen commence at 200°c. Methylenic linkage the ones susceptible to oxidation:
