Gel points are investigated as the critical extent ofreactionat gelation by FT-IR and viscoelastic measurements for the networkformed by the epoxyâamine system. The reaction systems examinedare comprised of diglycidyl ether of bisphenol A (DGEBA) and polyoxypropylene(POP) diamine of different chain lengths with various degrees of dilution.The experimental results are obtained as the delay of gel point, thatis the delay from the gel point expressed by the FloryâStockmayerformula, and interpreted in terms of ring formation caused by intramolecularreaction which is characterized by the ring forming parameter of λ0. This parameter relates with the internal concentration (inmol Lâ1) of reactive groups Pab, for RAfa Râ²Bfbtype polymerization. The analyses of the conversioncurve (pvs tcurve, where pdenotes the extent of reaction) obtained by FT-IR measurementare carried out on the basis of the kinetic model of the epoxy-aminereaction to find the ratio of rate constant. For all the reactionsystems, gelation occurs in excess of FloryâStockmayer gelpoint; the excesses are 0.09â0.15 in extent of reaction. λ0is determined from the gel point data through the pcâλ0relationship developedin the first part of this study, where the schemes of unequal reactivityand the states of reaction for POP diamine unit are incorporated.The gel point data are also applied to the pcâλ0relationship where these schemesare not incorporated. Following λ0, Paband the length of bond are derived and compared interms of the effect of difference in these schemes. [ABSTRACT FROM AUTHOR]