Mall.S provided a model of unequal reactivity of functional groups on the basis of the gelation phenomena. Stepto thought that the reason for the large difference of gel point between polyurethane and alkyd resins was due to the formation of cyclization and intramolecular reaction, then the rate theory was proposed. - Herrmann.H.J showed the effects of solvent in a kinetic gelation model. Irzhak V.I proposed the "bond block method" theory, which concept as a method to solve problems involving substitution over the conventional statistical approaches. Then Mittal.K, Klonowski, French.D.M., Robbins.D.J, and Selim kara proposed much more complex theories which could be found in the review literatures.