Unlike thermal degradation, where polymer scission can occur randomly and/or at the chain end, oxidative degradation is characterised by random scission in the polymer backbone. For instance, the addition of free-radical initiators to polyolefins during extrusion is used industrially to improve the mechanical properties of the polymer {864583}. The most important issues in thermooxidative degradation of polymers are where oxidation takes place, which structure fragments are most vulnerable, how they should be protected, and what are the main principles of protection.

Polymer degradation by adding peroxide is a common manufacturing technique because the controlled addition of peroxide to, for example, polypropylene leads to polymers with superior flow properties [a.34, a.35] {865102} {832500}. Addition of peroxide during the extrusion of polyethylene leads to an increase in the durability of the polymer [a.36]. Other studies include the addition of peroxides to blends of polyolefins and rubber to improve the mechanical properties due to the change in the polymer molecular-weight distribution (MWD) (molar-mass distribution) caused by the reaction with peroxide [a.34] {890265} {865094}. Many investigations of polymer thermal degradation have centred on determining the yield of monomer and the rate of change of average molecular weight.

Research has shown that PVC by itself degrades slowly and takes on a colour changing from light yellow to reddish brown at longer times [a.37]. When followed by its curves of HCl evolution, a small induction time to degradation is observed. Temperature does not affect the amount of HCl evolved, but only...