TEMPERATURE-DEPENDENCE OF THE BEHAVIOR OF A REACTIVE EPOXY-AMINE SYSTEM BY MEANS OF DYNAMIC RHEOLOGY .2. HIGH-T-G EPOXY-AMINE SYSTEM

A high-T-g epoxy-amine system based on diglycidyl ether of bisphenol A (DGEBA) and 4,4'-methylenebis[3-chloro-2,6-diethylaniline] (MCDEA) wa s studied near the gel point in isothermal conditions from 80 to 180 d egrees C by means of a rheological method, thus, below and above the g lass transition temperature of the fully cured network, T-g infinity ( T-g infinity = 177 degrees C). The lower limit of this temperature ran ge is close to T-gel(g) (T-gel(g) = 50 degrees C), the temperature at which gelation and vitrification occur simultaneously. Close to the ge l point, the power laws relating viscosity, eta, to epsilon(-k) and th e storage shear modulus, G', to epsilon(z) (epsilon = \x - x(gel)\/x(g el)) are verified above 150 degrees C. The scaling law partial derivat ive(log G)/partial derivative t proportional to omega(-k) is verified only at 170 degrees C (kappa = 0.25) and 180 degrees C (kappa = 0.18) . The exponents k and Delta are constant above 150 degrees C (k = 1.43 +/- 0.03, Delta = 0.69 +/- 0.01) and are very close to those found in the Rouse percolation model. Below 150 degrees C, these exponents dim inish as the curing temperature decreases. The exponent z is frequency dependent at a given temperature, and its value z(0) for omega = 1 ra d/s decreases with temperature. z(0) and k are found to be more sensit ive to the vitrification phenomenon than the parameters k and Delta. A t 180 degrees C, thus above T-g infinity, the values of exponents k, z (0), Delta, and kappa are in good agreement with those derived from th e percolation theory with macromolecular chains obeying the Rouse mode l. Below 150 degrees C, this behavior is no longer observed. These res ults are compared to those obtained for a low-T-g epoxy-amine system f or which only the gelation phenomenon occurs.