Temperature Dependence of the Behavior of a Reactive Epoxy−Amine System by Means of Dynamic Rheology. 2. High-T_g Epoxy−Amine System

Abstract

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) was studied near the gel point in isothermal conditions from 80 to 180 °C by means of a rheological method, thus, below and above the glass transition temperature of the fully cured network, T g ∞ (T g ∞ = 177 °C). The lower limit of this temperature range is close to gel T g (gel T g = 50 °C), the temperature at which gelation and vitrification occur simultaneously. Close to the gel point, the power laws relating viscosity, η, to ε- k and the storage shear modulus, G‘, to ε z (ε = |x − x gel|/x gel) are verified above 150 °C. The scaling law ∂(log G*)/∂t proportional to ω-κ is verified only at 170 °C (κ = 0.25) and 180 °C (κ = 0.18). The exponents k and Δ are constant above 150 °C (k = 1.43 ± 0.03, Δ = 0.69 ± 0.01) and are very close to those found in the Rouse percolation model. Below 150 °C, these exponents diminish as the curing temperature decreases. The exponent z is frequency dependent at a given temperature, and its value z 0 for ω = 1 rad/s decreases with temperature. z 0 and κ are found to be more sensitive to the vitrification phenomenon than the parameters k and Δ. At 180 °C, thus above T g ∞, the values of exponents k, z 0, Δ, and κ are in good agreement with those derived from the percolation theory with macromolecular chains obeying the Rouse model. Below 150 °C, this behavior is no longer observed. These results are compared to those obtained for a low-T g epoxy−amine system for which only the gelation phenomenon occurs.

Simultaneous kinetic and microdielectric studies of some epoxy-amine systems

“…It is observed that the agreement between experimental results and model calculations is good for the three epoxy-amine systems. Table II contains our values of rate constants, K 0 and K 1 , and of the times of gelation, t gel (gelation occurs at conversion 0.59 for DGEBA/ MCDEA and DGEBA/MDEA 20 and conversion about 0.6 for DGEBA/DDS 19 ). Also reported are the values of these parameters calculated using Arrhenius laws found by Girard-Reydet et al 19 The two sets of values are close.…”

Surface migration of fluorinated additive during the curing of epoxy resin

“…The diffusion coefficient (D) results from the competition between the driving force (which is the thermal motion, k B ÁT) and the friction term (f) which is dependent on the nature of the particle environment [22][23][24][25]. D is considered constant with time for a steady environment.…”

“…So, the curing temperature variation leads to 2 opposite effects and, in order to predict their influence onto the total diffusion (Q) it was necessary to develop Eq. (7) as a function of T [25][26][27]:…”

New anhydride/epoxy thermosets based on diglycidyl ether of bisphenol A and 10-undecenoyl modified poly(ethyleneimine) with improved impact resistance

“…Therefore, vitrification should be surpassed in order to get complete cure by increasing the curing temperature above the T g of the fully cured material. Rheometric monitoring of curing processes is a methodology used to determine accurately the gel point and vitrification because it is highly sensitive to the dramatic changes in the viscoelastic properties that occur [32,33,34].…”