Mechanismus der photopolymerisation des styrols, 3. Zur kinetik der photo‐elementarprozesse

Abstract

AbstractThe photoinduced free radical bulk polymerization of styrene (M)—in the absence of any sensitizer or free radical initiator—was investigated at different intensities, Ja, and at different wavelengths, λe, of the exciting light (λe = 313 nm, 335 nm; 25°C). The polymer conversion was followed dilatometrically in optical cells and the photo‐oligomers which are built up simultaneously in the polymerizing system —cis‐1,2‐diphenylcyclobutane (c‐CB), trans‐1,2‐diphenylcyclobutane (tr‐CB), 1‐phenyl‐1,2,3,4‐tetrahydronaphthalene (1‐PhT), 2‐phenyl‐1,2,3,4‐tetrahydronaphthalene (2‐PhT), 1‐phenyl‐4‐(1‐phenylethyl)‐1,2,3,4‐tetrahydronaphthalene (T1) and 2‐phenyl‐4‐(1‐phenylethyl)‐1,2,3,4‐tetrahydronaphthalene (T2),—were quantitatively analyzed by GLC. The quantum yields were found to be φc‐CB = 0,10, φtr‐CB = 0,02, Φ1‐PhT = 0,0084, Φ2‐PhT = 3,7.10−3, ΦT = 5,0.10−4, respectively, and from the experimentally observed dependence of the rate of polymerization, VP, on the square root of the light intensity, Ja, the apparent quantum yield of the formation of radicals can be calculated to be ΦS = 5,6.10−4. On the basis on the proposed structure of the photointermediates, I, which had been previously confirmed by 1H NMR spectroscopy in enriched systems, the kinetic treatment of the photostationary state gives a complete data set of mean values of partial quantum yields, φ, concerning all the photo‐elementary processes of I under polymerizing conditions: φS = 2,56.10−3, φT = 2,3.10−3, φPhT = 5,5.10−2 and φ2M = 0,94 (retro‐Diels‐Alder decomposition).