Abstract
Resol has been known to afford a hard resin by addition of acid. However this reaction has not been actively studied like the heat-hardening reaction, perhaps because of its poor valuability in industrial field. In the present paper, some articles written by E. Ziegler and G. Zigeuner (1947, 1948), K. Hultzsch (1947, 1950) and G. E. Little (1962) are reviewed. It seems conclusive that aromatic rings in the acidcatalysed resin are connected by methylene bridges (-CH2-), but the opinions are divided on the point that dimethylene ether bridges (-CH2OCH2-) are included or not.
Next “barrier pH” and the two step reaction of resorcinol-formaldehyde resins proposed by Little and K. W. Pepper (1947) are mentioned. Concerning the chemistry of polyhydric phenol resins, articles submitted by H. v. Euler et al (1940), R. A. V. Raff and B. H. Silverman (1951) and F. Yamada (1953) are referred.
