Radiation crosslinking of rubber. IV. Ultraviolet and infrared absorption spectra

When purified rubber is exposed in vacuo to high energy radiation, very few conjugated triene groups are formed relative to the number of molecules of hydrogen evolved. This indicates that less than 4% of the hydrogen is evolved from adjacent carbon atoms in the same molecule, a reaction which would have no immediate crosslinking potential. Rather more conjugated diene groups have been detected, but when these are compared together with triene groups relative to the yield of chemical crosslinks it can be calculated that less than 10% of the allylic radical precursors disproportionate. Infrared absorption spectra do not indicate the marked decrease in unsaturation reported by some previous workers. Slight changes in the infared spectra may indicate some cis‐trans isomerization. There is qualitative evidence for a small increase in vinylidene unsaturation.