FOURIER-TRANSFORM INFRARED AND C-13-NMR SPECTROSCOPIC CHARACTERIZATION OF MODEL EPOXY NETWORKS

Model epoxy networks based on a diglycidylether of bisphenol A (DGEBA) or of butanediol (DGEBU) and cured with different mixtures of monoamines and diamines were prepared to allow changes in cross-link density. The choice of aliphatic or aromatic amines permitted assessment of the influence of network chain flexibility. Solid state C-13-NMR spectra showed that no secondary reactions leading to the creation of ether linkage occur during the condensation reaction. Glass transition temperatures (T(g)) and the temperatures of the maximum of the exothermic cross-linking reaction (T(exo)) were determined. A rectilinear increase of T(g) as a function of the density of cross-links was observed for all the systems under study. Similarly, an increase in the stiffness of the backbone units resulted in an increase in T(g). Time-temperature-transformation (TTT) isothermal cure diagrams were constructed and infrared kinetics were performed at 90-degrees-C. Gelation and vitrification times were shown to be dependent on the nature of the amines used to create the network structure.