Mechanism of dissolution inhibition in phenolic resins

It was suggested in an earlier communication that dissolution inhibition in phenolic resins comes about through the blocking of some of the hydrophilic OH-groups by a hydrophobic effect of the inhibitors. Honda et al. have shown that the hydrophobicity of the additive is not a sufficient condition, and that the polar groups of the inhibitor, such as the diazoquinone function, play an important role in the inhibition effect. They found that additives with very similar skeletal structures, but differing in the polar anchor group, have very different inhibition efficiencies in a common novolac resin. In this study we investigate the interaction between phenols and the anchor groups of the inhibitors by determining the equilibrium constants of their association reaction. From this, the fraction of bound acceptor groups (inhibitors) can be estimated for the casting solution of the films at the point of solidification. It can be shown that this fraction correlates quite satisfactorily with the inhibition effect of the additives used in Honda's study.