C-13 solid-state NMR analysis of the DGEBA/TETA epoxy system

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.