Dielectric analysis of epoxy-amine systems. 1. Conductivity and gelation

To try to observe gelation phenomenon from the dielectric curves, the low-T-g epoxy-amine system (T-g infinity = -12 degrees C), based on diglycidyl ether of 1,4-butanediol (DGEBD) and 4,9-dioxa 1,12-dodecane diamine (4D) was studied during isothermal curings by means of microdielectrometry. The isothermal curings were done at 40, 50 and 60 degrees C. At these temperatures, this system only exhibits gelation phenomenon. Three different approaches were developed: (i) inflexion point as gelation criterion; (ii) percolation theory; (iii) correlation between conductivity and viscosity. The first approach shows that the inflexion point is not the gel point. Both other approaches fail to describe the complete evolution of the epoxy-amine reactive systems during cure. This is due to the fact that at the gel point, the macroscopic viscosity diverges, whereas the conductivity values involve the ion motions, thus the local viscosities. So, there is no manifestation of gelation on dielectric curves. (C) 1999 Elsevier Science Ltd. All rights reserved.