Radiation-induced discoloration of polymers

There is growing interest in radiation-induced changes in absorption spectra of polymers due to: (1) the need for optical-property materials in radiation environments and (2) the problem of discoloration in radiation-processing. The authors report an investigation of complex optical-property changes in 16 major types of transparent polymers. Irradiated polymers form both permanent color centers (associated with conjugated chromophores) and annealable color centers (associated with conjugated radicals); the amount and ratio vary greatly, and are governed by the oxygen permeability coefficient and the dose. A non-oxidative annealing mechanism is also operative. The relative resistance of different polymer types toward radiation-induced discoloration does not correlate with their relative resistance to radiation-induced mechanical property changes, and is not strongly influenced by the presence of aromaticity