γ‐Irradiation of poly(ethylene terephthalate). I. Yields of gas and carboxyl groups

Poly(ethylene terephthalate) was exposed in vacuo γ‐radiation from a Co 60 source at a dose rate of 0.02 Mrad/min., and an ambient temperature of 47°C. Gaseous products were analyzed in a mass spectrometer and carboxyl groups estimated by titration with NaOH and by infrared analysis. Initial G values were COOH = 0.77, CO 2 = 0.17, CO = 0.11, H 2 = 0.015, and CH 4 = 0.003. All these values decreased markedly with increasing dose except G (CO) 2 , which, roughly, was maintained up to 5000 Mrad. It was considered whether the dependence on dose of the yields of the major reaction products could be accounted for by the following set of first‐order reactions: magnified image It was found that the rate of formation of COOH groups at low doses was much too high to fit this simple reaction scheme. However, a better fit was obtained over a range of higher doses (ca. 100–5000 Mrad). A final conclusion could not be reached concerning the validity of the above reaction scheme.