The photolysis of polyethylene terephthalate

Abstract

AbstractThe photolysis of films of polyethylene terephthalate has been studied over a wide variation of exposure conditions. The rate of polymer bond rupture was measured by the change in molecular weight. The rate of energy absorption upon exposure to near ultraviolet light was determined from an analysis of the emission characteristics of the light sources used and the absorption characteristics of the polymer. The overall quantum yield for the photolysis was found to be 5 × 10−4 bonds ruptured per photon. This quantum yield is shown to be independent of the wave length of the light absorbed in the spectral region studied. Further, analysis of the effect of film thickness on the rate of bond rupture indicates that the reactions are initiated only by the light absorbed in the strong ultraviolet absorption band characteristic of the pure polymer. The quantum yields for the photolysis of this polymer and others reported in the literature are compared and related to the effect of changes in physical state on the reactions of simple monomeric systems. It is concluded that the low values typical of many polymers are a result of rapid recombination of free radicals due to a low mobility in the solid state.