Controlled synthesis of high‐ortho‐substitution phenol–formaldehyde resins

The relationship between the use of 19 kinds of metal catalysts and the proportion of ortho–ortho links of novolac resins was studied. The proportion of ortho–ortho links of novolac resins was characterized with Fourier transform infrared, 1H‐NMR, and 13C‐NMR. The effects of different catalysts and different reaction conditions, such as the molar ratio of phenol to formaldehyde, the pH value of the reaction, and the reaction time, were examined. Phenol–formaldehyde resins were synthesized with a certain proportion of the ortho position through the adjustment of the reaction conditions.