Abstract: An interpretation of the effect of resin molecular weight on the dissolution of novolak is offered. It is based on Eyring's transition state theory and on the percolation model of novolak dissolution. The rate determining step of novolak dissolution is the deprotonation of phenol by base at the front edge of the penetration zone. In order for this reaction to occur, an ion pair of base must appear at the interface of the penetration zone with the virgin matrix. To make this possible, all base ions of the corresponding percolation channel have to move forward in synchronism, and this requires the simultaneous thermal activation of all the sites of the channel. At this point the mechanism of energy transport in an ensemble of polymer chains intervenes: thermal (vibrational) energy propagates much faster along the chains then between them. It can be shown that the probability that a particular site will receive an activating quantum is inversely proportional to the length of the chain to which the site belongs. The application of these principles leads to a quantitative description of the activation entropy and the activation energy, and hence of the rate of novolak dissolution as a function of resin molecular weight.!7
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