Formation of acetophenone groups

It is generally accepted that acetophenone end-groups are formed during UV irradiation of polystyrene and it is most probable that they are responsible for the yellow coloration of a polymer. Molar absorptivity of acetophenone groups at 240nm is e= 1.4 x 10 lmol cm and the apparent quantum for their formation is / = 9 x 10 . They have an IR absorption band at 1685-1690cm- [745]. 

The stationary concentrations of hydroperoxides in photo-oxidized polystyrene are low [2204, 2242] however, formation of polymeric hydroperoxides initiates further photo-oxidative reactions, with carbonyl species only appearing once the hydroperoxide concentration reaches a steady state [1661]. 

Thermal decomposition of the in-chain peroxides (cf. section 3.11.1.7) during polymerization and/or processing [341, 725]  

Acetophenone groups absorb UV irradiation and may participate in a number of photochemical reactions  

Triplet excitation of a carbonyl group and formation of an end-ketyl radical (5.83)  

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