HIGH-RESOLUTION SOLID-STATE C-13 NUCLEAR-MAGNETIC-RESONANCE INVESTIGATION OF LOCAL MOTIONS IN MODEL EPOXY-RESINS

The local dynamics of some 'model' epoxy networks based on various diepoxides and diamines was investigated in the bulk state using high-resolution solid-state C-13 nuclear magnetic resonance. The strength of the C-13-H-1 dipolar coupling was determined from the rises of C-13 magnetization in cross-polarization experiments using very short contact times. A restricted motional averaging of the C-13-H-1 dipolar coupling was observed below the glass transition temperature for the hydroxypropyl ether groups and methylene carbons adjacent to the crosslinks, indicating the existence of local motions of these units in the tens of kilohertz range. The extent and temperature dependence of the motional averaging depend on the chemical structure of the epoxy network considered. Comparison with results derived from dynamic mechanical experiments leads to the conclusion that the motions of the hydroxypropyl ether groups are likely to participate in the phenomena responsible for the beta secondary relaxation. Moreover, the relatively high mobility of the central methylene units in the aliphatic sequences of the diglycidyl ether of the butanediol-based network, and of the hexamethylenediamine-based network, can be associated with the gamma relaxation of epoxy networks.