Chain stabilisation stopping

Figure 3.17 Alkaline chain stabilisation (stopping) reactions of cellulose.

Polymer is degraded by heat, energy, UV or residues of catalyst and generates alkyl radicals. This alkyl radical reacts with oxygen and form peroxy radicals. These peroxy radicals abstract hydrogen from other polymer and forms alkyl radicals and hydroperoxide. The decomposition of hydroperoxide to alkoxy and hydroxyl radicals induces additional decomposition of the polymer chain. In order to stop the radical chain reaction of degradation, stabilisers such as phenolic antioxidant, phosphites, thioether and hindered amine light stabilisers (HALS) are added. 

Polyene formation is not necessarily stopped altogether by a heat stabiliser, but it can be restricted to short sequences of a few (say five) carbon-carbon bonds, so that the polymer does not absorb too much light in the visible region of the spectrum, causing colour changes. This also discourages crosslinking and/or chain scission. 

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