An electron spin resonance study of radical transfer reactions in γ‐irradiated vinylthiol/styrene‐copolymers

Formation and behaviour of radiation induced free radicals in statistical copolymers from vinyl hydrosulfide and styrene (1:1, 1:4, and 1:10) were investigated by means of ESR spectroscopy. The corresponding homopolymers were also included in these studies. After γ-irradiation of the copolymers at 77 K and subsequent annealing to 293 K it was possible to detect thio radicals. Their relative yields were found to increase with increasing styrene content. Investigations regarding the thermal behaviour of the radiation induced radicals in the copolymers allowed the assumption of two mechanisms responsible for the formation of the thio radicals: First, the formation takes place via ion radicals located at the mercapto groups at 77K. In the copolymers the stability of the thio radicals is favoured by steric hindrance through the benzene rings thus reducing the formation of disulfide bridges as termination reaction. Secondly, the formation of the thio radicals is caused by a hydrogen transfer from the mercapto groups to the benzyl radicals and/or cyclohexadienyl radicals of styrene units.