Mechanical properties measurements, like Charpy impact tests, provided evid
ence that the macromolecular network of the epoxy system formed by the hexa
functional triethylene tetramine hardener, TETA, with the diglycidyl ether
of bisphenol A monomer, DGEBA, can be modified by changing the hardener con
tent. The previously analyzed monomer-to-hardener ratios were here studied
by C-13-NMR solid state techniques. The results from crosspolarization/magi
c angle spinning (CPMAS) C-13-NMR spectra, together with the evaluation of
proton spin-lattice relaxation time in the rotating frame (T(1)(H)rho), dis
play the behavior of these epoxy/hardener mixtures considering the mobility
and interaction of molecular segments present at the macromolecular struct
ure. The results also show that the epoxy-rich mixtures form tight, and the
refore brittle, structures as previously observed by mechanical tests. The
stoichiometric monomer-to-hardener ratio is a transition point where an inc
rease in the mobility was found. For the amine-rich mixtures the obtained r
esults suggest the presence of domains with different segmental mobilities.
(C) 2000 John Wiley & Sons, Inc.