. . . "As the polymerization inhibitor, there can be used, for example, p-methoxyphenol, hydroquinone, hydroquinones substituted with an alkyl group such as methyl or ethyl or an aryl group such as phenyl, t-butylcatechol, pyrogallol, cuprous chloride, phenothiazine, chloranil, naphthylamines, ??-naphthol, 2,6-di-t-butyl-p-cresol, pyridine, nitrobenzene, dinitrobenzenes, p-toluidine, Methylene Blue and c" . . .