THE DENSITY OF CHEMICAL CROSS-LINKS AND CHAIN ENTANGLEMENTS IN UNFILLED EPDM VULCANIZATES AS STUDIED WITH LOW-RESOLUTION, SOLID-STATE H-1-NMR

The network density in unfilled EPDM vulcanizates was studied by the f ollowing methods: low resolution, proton T-2 NMR relaxation, Mooney-Ri vlin analysis of stress-strain curves, and equilibrium swelling experi ments. For the vulcanizates as such, the NMR method measures the total network density, which is composed of chemical crosslinks (CC) and of temporary (EN/TE) and trapped chain entanglements (EN/TR). The estima ted molar mass of EPDM chains between apparent chain entanglements (EN ) is 1900 +/- 200 g/mol. For partially swollen samples, the NMR method determines the network density composed of CC and EN/TR. The CC densi ty is obtained from the total density of network junctions and the mea sured entanglement density assuming that CC and chain entanglements ar e decoupled and additive. The contribution of CC, EN/TE and EN/TR to t he total network density is estimated.