アルキルチオウレアおよび芳香族チオウレア誘導体のオゾン劣化防止効果

概要

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In order to estimate antiozonant efficiencies of thiourea derivatives, consumption rates of thioureas by ozonization in ethanol and the efficiencies (Eγ) of thiourea to prevent the viscosity decrease of cis-1, 4-polyisoprene in chloroform or monochlorobenzene solution were determined. In the latter case, Eγ is defined as Eγ=ηγ/ηγ0 where ηγ is the ratio of viscosities before to those after ozonization under a given condition in the presence of thiourea, and ηγ0 the same one in the absence of thiourea. The consumption rates and the values of Eγ indicated that the antiozonant efficiency decreases as the number of substituents of thioureas increases from mono-to di-and from di-to tri-substituted ones and also as the alkyl substituent of 1, 3-disubstituted thiourea becomes longer from methyl to ethyl and so on. Antiozonant efficiency of thiourea substituted with branched alkyl group was found to be lower than that substituted with the corresponding normal alkyl one. The values of Eγ of the aryl-substituted thioureas, in general, were less than those of the alkyl thioureas. However, Hammett's equation clearly holds betweenσ constant and log Eγ of substituents on the aryl-substituted thiourea. These results indicate that electronreleasing group increases the antiozonant efficiency of thiourea while the electron-attracting group decreases it.
日本ゴム協会の論文