THE CURING OF EPOXY-RESINS AS STUDIED BY VARIOUS METHODS

The sol-gel-glass transformations were examined in the thermosets of d iglycidyl ether of bisphenol A (DGEBA) and diglycidylaniline (DGA) cur ed with 4,4'-diaminodiphenylmethane (DDM) at 70 degrees C by using tim e-resolved fluorescence, Fourier-transform (FT) Raman spectroscopy, an ultrasonic technique and torque measurements. The rotational correlat ion times of substituted styryl and cyanine dyes showing a twisted int ramolecular charge-transfer increase as the isothermal cure reaction p roceeds and are sensitive to gelation. The chromophores detect the loc al viscosity of the surroundings. In the case of DGEBA/DDM, the extent of the epoxide ring reaction, obtained from FT-Raman studies over the whole curing process, was used to determine the variation of the glas s transition temperature and the reduced free volume during crosslinki ng. Thus, it was possible to relate quantitatively the increase of the rotational correlation time of the dyes to the decrease of the reduce d free volume. The variation of the ultrasonic velocity and absorption in the course of curing indicates vitrification (dynamic glass transi tion), but shows no characteristics with respect to gelation. Differen ces in the curing behaviour of DGEBA/DDM and DGA/DDM were clearly evid ent.