Application of the percolation model to gelation of an epoxy resin

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Abstract
The percolation model has been applied to the study of gelation of the TGDDM‐DDS system (tetraglycidyldiaminodiphenylmethane–diaminodiphenylsulfone) at a mass concentration of 100–30. For each temperature the experimental viscosity curves are satisfactorily described by a percolation law. Using the degree of chemical reactions, X, as a variable, a very clear change in the reaction mechanism with temperature can be shown. Then a rate of advancement of effective reactions, Y, is defined. This value only takes intermolecular‐type reactions into account, and is probably the only variable on which viscosity depends in a percolation law: η = B(1 − Y/Yc)−p. We obtain Yc= 0.45 and p= 2.0. Comparing Xc and Yc at the gel point, we obtain information on the proportion of intramolecular reactions with temperature. It is also demonstrated that the critical percolation threshold agrees closely with the gel point determined experimentally on log G″= f(t) curves.