Determination of Structure and Reaction Kinetics of Epoxy/Amine Systems Using Magnetic Resonance

摘要

Electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) were used to investigate: (1) the kinetics of the reactions between amines and epoxies; (2) the dependence of molecular mobility on temperature and crosslink density of the host epoxy matrix; (3) the number of unreacted amine and epoxy functional groups trapped in amine-cured epoxy samples; (4) the measurement of the composition of amine-cured epoxies, and (5) the utility of two-dimensional 13C NMR to characterize slow molecular motion in cured epoxies. In the EPR experiments, stable nitroxide free radicals were used as spin labels and spin probes. The changes in EPR line shapes were used to monitor the rates of formation of the initial addition products in the reactions between the epoxy tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM) and two model compounds, a secondary amine nitroxide and tertiary amine nitroxide. In amine-cured epoxy host matrices at all temperatures, the EPR line shape of the spin probe can be characterized by one value of the rotational correlation time. Hydrogen BNMR measurements of the spin-spin relaxation times and spin-lattice relaxation times were obtained during the cure of epoxy MY720 (Ciba Geigy) with the amine Eporal (Ciba Geigy).