Tetrahydrofuran flash photolysis

In order to demonstrate the use of laser flash photolysis in elucidation of the MDI based polyurethane photolysis mechanism, three polyurethanes, two aryl biscarbamate models, an aryl monocarbamate model, and an aromatic amine were selected. Two of the polyurethanes are based on MDI while the third is based on TDI (mixture of 2,4 and 2,6 isomers in 80/20 ratio). The MDI based polyurethanes all have the same basic carbamate repeat unit. The MDI elastomer (MDI-PUE) is soluble in tetrahydrofuran (THF). The simple polyurethane (MDI-PU) based on MDI and 1,4-butanediol is used in the tert-butoxy abstraction reactions since it does not contain a polyether backbone. (See page 47 for structures of polymers and models.)... 

These interpretations were supported by time-resolved spectroscopy. Laser flash photolysis of 4 in CH2C12 produces a transient spectrum (Figure 11) very similar to that obtained by flash photolysis of phenyl azide (Figure 8) and is therefore attributed to pentafluorodehydroazepine. Similar results were obtained in acetonitrile and tetrahydrofuran. However LFP of 4 in methanol gives an entirely different transient spectrum. (Figure 12). The... 

The addition of sodium to aromatic hydrocarbons produces only the corresponding radical anion [121]. Alkali metals, however, dissolve in aliphatic ethers, e.g. tetrahydrofuran, dioxan, producing the characteristic blue colour [122], The solutions are diamagnetic because of the formation of higher ion pairs. Flash photolysis of solutions of sodium in ethers forms the ion pair consisting of the solvated electron and a sodium cation [123]. Three transients are formed in the flash photolysis of sodium pyrenide in tetrahydrofuran [124]. These have been identified as the solvated electron, es"oiv. the ion pair, esoiv> Na, and the sodium atom, Na°. Rate coefficients of reactions of es ,iv with various compounds relative to the rate of reaction with NjO have been determined recently by the 7-radiolysis of 2-methyl-tetrahydrofuran [125]. 

Liu et al. (1990a), using a flash photolysis-resonance fluorescence technique, obtained k = 3.75 X 10" cm molecule" s" for reaction of 0( P) with tetrahydrofuran. 

Rate coefficients for reaction of OH with 2-methyl-tetrahydrofuran have been reported over a range of temperatures by Wallington et al. (1990e), see table III-E-8 and figure III-E-5. Fitting of their combined relative rate and flash photolysis data gives... 

The vapor phase photolysis of ethylene oxide has found more attention than that of its higher homologs. It has first been extensively studied by Corner and Noyes (193) in the long wavelength region. Fleming et al. studied the effect of ring size on the photolysis of cyclic ethers such as ethylene oxide, oxetane, and tetrahydrofuran (90). Roquitte (194) did flash... 

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