Abstract
On irradiation with uv light, changes in uv and ir spectra were observed. In the uv spectrum, a minimum at 290 nm due to sulfur, dibenzothiazyl disulfide, and double bonds in the main chains disappeared initially by the consumption of them; but the minimum reappeared on further irradiation reflecting the formation of carbonyl groups. On the other hand, in the ir spectrum two absorption bands appeared at 1720 cm−1 (due to carbonyl groups) and 3450 cm−1 (due to hydroxyl groups). The latter band faded out suggesting the decomposition of hydroperoxides when the vulcanizate was kept in the dark after irradiation. From the findings of the wavelength dependence of photo-oxidation on uv and ir spectra, it was found that the degradation occurred below about 430 nm. However, investigation of the wavelength dependence of photo-oxidation by the measurement of the crosslink density gave the results that crosslinking reactions occurred below about 340 nm, scissions of C-C and polysulfide crosslinks between 340 and about 400 nm, and scissions of polysulfide crosslinks between 400 and 600 nm. These were confirmed by measurements of the dynamic modulus during irradiation. The relative modulus E′(t)/E′(0) increased on irradiation with light at 253.7 nm in a longer time region reflecting a crosslinking reaction. On the other hand, on irradiation with light above 330 nm, E′(t)/E′(0) decreased with time. Change in E′(t)/E′(0) could be represented by the equation of the first order reaction containing an exponential term and the rate constant was determined. The activation energy was calculated as 18.6 kcal/mole from the temperature dependence of the rate constant and agreed with that for scission of polysulfide crosslinks. The photodegradation of the IR vulcanizate occurred also on irradiation with visible light (> 430 nm), and the modulus decreased.
Bilirubin photoconversion induced by monochromatic laser radiation. Comparison between aerobic and anaerobic experiments in vitro
