Thin films of poly(methyl methacrylate) (PMMA) at about 25°C. irradiated with a medium‐pressure mercury lamp undergo random scission with a quantum yield of 0.039 and 0.017 scissions/quantum absorbed in vacuum and in air, respectively. Crosslinking in air was not observed. Quantum yields for scission were independent of intensity. Volatile products included methyl formate, methyl methacrylate, and methanol in quantum yields of 0.14, 0.20, and 0.48 molecules per quantum absorbed, respectively. During irradiation in either vacuum or air, the ultraviolet absorption of PMMA increases with a band at 285 mμ, attributed to carbonyl groups in the polymer itself. A mechanism for the photodegradation of PMMA is suggested.

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Thin films of poly(methyl acrylate) at room temperature have been photodegraded in air and in vacuum by radiation from a low‐pressure mercury source. Changes in intrinsic viscosities, ultraviolet absorption, and volatile products were followed as a function of the energy absorbed. Crosslinking occurs in both air and vacuum, but at a slower rate in air. The apparent quantum yield for random scission in air was 0.013 scissions per quantum absorbed. In air, carbonyl groups are formed along the backbone chain. Most of the volatile products studied appear to orginate from the ester groups in the polymer; formaldehyde, methanol, and methyl formate evolved at a constant rate for doses up to at least 2 × 1020 quanta/g.; quantum yields for each were determined. Carbon dioxide forms in amounts increasing exponentially with dose. Small amounts of carbon monoxide, methane, and hydrogen were detected qualitatively, but monomer was not observed. A mechanism compatible with these findings is suggested.

The vacuum ultraviolet absorption spectra of bicycloheptane and bicycloheptene have been investigated in the region from 45 000 to 65 000 cm—1. Two distinct band systems with maxima at 51 125 and 59 715 cm—1 were noted in the case of bicycloheptene, each with an oscillator strength of 0.15. The first observed absorption of bicycloheptane was near 55 000 cm—1 while that of the unsaturated hydrocarbon was displaced more than 8000 cm—1 toward lower frequencies. In both compounds, sharp narrow bands were superimposed on the continuous absorption. In a study of the photodecomposition, it was shown that cyclopentadiene and ethylene were formed as photodecomposition products of bicycloheptane and also of bicycloheptene.

The photodegradation of thin films of poly‐α‐methylstyrene by near ultraviolet radiation has been studied in vacuum at 27 and 115°C. Changes taking place during photolysis were followed by a determination of monomer formation by ultraviolet spectroscopy, residue molecular weight through a measurement of intrinsic viscosity, and volatile products by mass spectroscopy. Gross features of the photolysis include random chain scission in the polymer with subsequent depolymerization of the radicals formed to yield small amounts of monomer; the kinetic chain length is on the order of 15 in the temperature range studied. Quantum yields at 27°C. for chain scission and monomer formation are 1 × 10−3 and 7 × 10−3, respectively. At 115°C. the quantum yields are 2 × 10‐2 and 0.5. Small quantities of hydrogen, CO2, CO, and a number of hydrocarbons were liberated during irradiation. An approximate one‐to‐one correlation between the number of main chain scissions and CO2 + CO molecules evolved was found, suggesting the occurrence of chain scission at weak linkages involving oxygen.