Poly o-, m- and p-substituted styrenes

Mechanisms of photodegradation of 0-, m- and p-alkyl substituted polystyrenes (5.88) are similar to each other, but there are significant differences 

The mechanism of photodegradation can be presented by the following reactions, using as an example poly(p-ethylstyrene) (3.88) [2258]  

Formation of polyene structures causes yellow colouring of a polymer sample. Chain scission and crosslinking occur simultaneously. Rates of crosslinking are greater than those of polystyrene and this is attributable to the participation of the substituted phenyl radicals (formed by phenyl-alkyl group fission) in addition reactions. However, crosslinking is inhibited sterically, to some extent, in the poly(o-alkylstyrenes). 

Poly(p-halogenostyrenes) exhibit a very similar photodegradation mechanism [2250]. 

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