Radiation Induced Changes in the Structure of Polyisobutylene

Polyisobutylene suffers random main-chain fracture when exposed to high radiation. Identical results are produced by electron and γ-radiation and the average energy absorbed per break amounts to 20 eV at 20° C. The unsaturation produced is proportional to the number of breaks. A new absorption band appears in the infra-red at 11.25μ, which indicates that a vinyl double bond of the type R1R2C═CH2 has been introduced. The gases evolved on irradiation have been analyzed. A chemical mechanism for the degradation has been proposed. The energy per break varies with temperature, the relationship being somewhat similar to the inactivation behaviour of ionizing radiation on certain biological systems. The ultra-violet absorption spectrum is different for polymers which have been irradiated in vacuum or nitrogen from those irradiated in air but the number of main-chain breaks is not affected by the surrounding gas.