ESR study of free radicals formed by γ‐irradiation of poly(ethylene terephthalate)

Free radicals formed by γ‐irradiation of oriented samples of poly(ethylene terephthalate) (PET) were studied at 25°C. by ESR spectroscopy. The G value for trapped free radicals is 0.02. The predominant radical is identified as $\text{O} - \text{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{C} H} - \text{CH}_\text{2} - \text{O} -$ , and a minor component of the spectrum is tentatively assigned to the radical COĊ₆H₃CO. The absence of cyclohexadienyl type radicals is discussed. Previously reported dose rate effects in PET are explained by reference to a chain reaction involving β‐bond scission of the radical $\text{O} - \text{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{C} H} - \text{CH}_\text{2} - \text{O} -$ .