A PERCOLATION VIEW OF NOVOLAK DISSOLUTION AND DISSOLUTION INHIBITION

The dissolution of novolak and other phenolic resins in aqueous alkali is controlled by the diffusion of developer base through a thin penetration zone which separates the matrix from the developer solution. Diffusion of base through the zone is a percolation process which may be described by a scaling law of the form R = constant X (p - p(c))2. Here R is the dissolution rate, p is a percolation parameter which is proportional to the concentration of phenol groups in the solid resin, and p(c) is a percolation threshold below which dissolution does not occur. The scaling law of percolative dissolution was tested and confirmed on a group of partially methylated poly(vinylphenol) resins. Theory predicts a relation between the inhibition effect and the rate of dissolution which may be summarized by the expression -d log R/dc(i) = f(ij) = alpha(i) d log R/dp = alpha(i) (2 log e)/(p - p(c)). This has been confirmed by experiment. The constant alpha(i) is an absolute measure of the inhibition capability of an additive without reference to a specific resin.