Mechanism of the radiation-induced crosslinking of copolymers of chloromethylstyrene and methylstyrene

Mixtures of benzyl chloride with o- and p-cymene (CY) have been used as low molecular weight models of copolymers of chloromethylstyrene with o- and p-methylstryrene. The products of u.v. photolysis have been analysed using NMR and gas chromatography/mass spectroscopic techniques. From the benzyl chloride/pCY system, products arising from benzyl-benzyl, benzyl-alpha and alpha-alpha radical combinations were identified together with aromatic substitution products, whilst for the corresponding oCY system, markedly reduced yields of products arising from alpha radicals were observed. The sensitivity of the modelled copolymers to radiation induced crosslinking accords with these observations. The conclusion that o-methyl substituents sterically hinder the radical coupling reactions that afford crosslinks is discussed with due regard given to polymer chain flexibility. (author)