Chemorheological and dielectric study of epoxy-amine for processing control

Abstract

The curing of an epoxy prepolymer based on diglycidyl ether of bisphenol A (DGEBA) with isophorone diamine (IPD) as a hardener was analysed using differential scanning calorimetry, rheological measurements, microdielectrometry, and insolubles in THF for gel point detection. The effects of the initial hydroxyl concentration of the DGEBA prepolymer, the molecular features of which are different, were determined on the cure kinetics of epoxy networks Chemical reaction kinetics of this DGEBA/IPD system during isothermal conditions was studied in the 60–120 °C temperature range and a kinetic model relation based on assumption of an autocatalytic mechanism has been proposed. Gelation and vitrification phenomena of this reactive mixture were studied and allowed us to establish the TTT diagram. Furthermore, dielectric data and viscosity measurements have been interpreted with respect to kinetics. Indeed, it was shown that the modified percolation law equation suggested by Macosko et al can be used to describe the chemoviscosity as a function of temperature and extent of reaction by using a temperature- and conversion-dependent critical exponent. In other respects, dielectric properties such as ionic conductivity were related on one hand to viscosity through a Stokes-based equation in the 0 to 0.5 conversion range, and on the other hand to conversion through an experimental equation. © 1999 Society of Chemical Industry