The Vulcanization of Rubber with Phenol Formaldehyde Derivatives. I

Referring to Part I, describing the methylene quinone theory of the vulcanization of rubber with phenol-formaldehyde derivatives, in this paper the arguments in favor of that theory are considered in detail. The results of the investigations in question can be summarized as follows. 1. The vulcanizing properties of the pseudophenol halides are based on the easy transformation of these compounds into methylene quinones, with liberation of gaseous hydrogen halide. 2. The vulcanizing properties of the phenol-dialcohols are also based on the formation of methylene quinones as intermediates, but only at higher temperatures. 3. Phenol-dialcohols vulcanize slowly at temperatures only slightly below their decomposition temperatures, and yield comparatively good vulcanizates. Pseudophenol halides vulcanize rapidly at temperatures considerably below their decomposition temperatures, and yield comparatively poor vulcanizates. 4. The vulcanization temperature of 4,6-dihydroxymethyl-2-methylphenol (about 200° C) is higher than that of 2,6-dihydroxymethyl-4-methylphenol (about 155° C), as in the first case the vulcanization is based on the formation of an o-methylene quinone as well as a p-methylene quinone, and in the second case on the formation of o-methylene quinones exclusively. Generally these last compounds are formed more easily than the p-isomers. 5. The vulcanizing properties of 2,6-dihydroxymethyl-4-methylphenol at 155° C are reduced by the addition of 4,6-dihydroxymethyl-2-methylphenol, in consequence of the formation of molecular complexes which are unable to form o-, but only p-methylene quinones. 6. The vulcanizing properties of phenol-formaldehyde derivatives are entirely destroyed by hexamethylenetetramine, as that substance combines with the methylene quinones first formed. 7. The vulcanization reactions of the phenol-formaldehyde derivatives are not based on the formation of an irregular knot of entangled rubber and resin molecules, but on primary chemical bonds between these two. 8. The vulcanizing properties of the esters of the phenol-dialcohols, as well as those of the pseudophenol halides, are based on the formation of methylene quinones as intermediates, with liberation of acids. The higher fatty acid esters of 2,6-dihydroxymethyl-4-methylphenol are unstable, with the liberation of acids already at room temperature. 9. Compounds which may be supposed to be derived from phenol-dialcohols by a change in their configuration do not show vulcanizing properties if the formation of methylene quinones is impossible. If a repeated formation of these intermediates is only possible to a very limited extent, as is the case with phenol-monoalcohols, vulcanizing properties are also present on a minor scale.