Radical decay and color formation at various temperatures in unplasticized poly(vinyl chloride) irradiated in vacuo at 25°C

Abstract

Moldings were irradiated at ambient temperature in vacuo with 2 m.e.v. electrons to doses of 5.9–7.3 Mrad. The decay of radicals was followed by EPR spectroscopy at 80, 55, and 30°C. while simultaneous extinction measurements were made at 300–700 mμ with a recording spectrophotometer. The radical decay data indicated the presence of three species at each temperature, decaying exponentially with time, with half‐lives of 20 min., 210 min., and 135 hrs. at 80°C. of 40 min., 400 min., and 141 hrs. at 55°C., and of 54 min., 720 min., and 3200 hrs. at 30°C. G values of 1.6, 2.0, and 1.4 were obtained for radical formation at 25°C. by back‐extrapolation of decay curves from the three temperatures to the end of the irradiation period. The activation energy of radical decay was found to be 4.4, 5.0, and 13.7 kcal./mole for the short‐lived, intermediatelived, and long‐lived radicals, respectively. The optical data has a broad absorption maximum at 500–550 mμ and a series of seven absorption peaks with maxima at 505–510, 483–485, 458–460, 430–435, 400–405, 364–365, and 329–330 mμ. The concentration of the material producing the broad bands was found to be inversely proportional to the long‐lived radical concentration. The fine‐structure peaks are consistent with literature data for a polyene chain of 16–17 conjugated double bonds.