AbstractIn the vacuum photolysis of polystyrene films at 28°C. under 2537 A. radiation the only gaseous product is hydrogen. At the same time the polymer becomes insoluble and discolors. The intensity exponent of the reaction is unity, the quantum yield of hydrogen is 4.3 × 10−2, the overall energy of activation is 2.9 kcal./mole, and the rate of photolysis is independent of molecular weight. No hydrogen is produced when 3650 A. radiation is used. These observations can be interpreted in terms of a simple reaction scheme in which the primary effect of the 2537 A. radiation is to liberate hydrogen atoms. The subsequent reaction of these and the polystyryl radicals simultaneously formed in a number of competing steps results in the appearance of hydrogen, the occurrence of crosslinking, and the production of carbon–carbon unsaturation in the main chain which ultimately leads to conjugation and color. These theories are supported by infrared and ultraviolet spectral measurements and by the observation that the rate of photolysis is accelerated by nit
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