Conclusion on Motions in Antiplasticised Epoxy Networks

The dynamic mechanical analysis unambiguously shows that the antiplasticiser acts mainly on the cooperative motions involved in the high-temperature side of the p transition peak, implying several units. No effect is detected on the low-temperature side of the P peak. 

The NMR experiments clearly show a different effect of the antiplasticiser on the mobility of either the crosslink points (CH2 - N) or the hydroxypropyl ether sequence. Indeed, whereas these two groups have similar mobility in pure epoxy networks, the mobility of the crosslink points is hindered by the antiplasticiser, whereas only a slight slowing down occurs for the HPE units. Furthermore, there is no difference in mobility between the HPE sequence in the epoxy network and the one in the antiplasticiser molecule. 

On the other hand, the investigations performed on pure epoxy networks unambiguously assign the /3 transition to motions of the HPE sequence. 

The important feature is the occurrence of a partial breakdown of interchain cooperativity. 

In the case of epoxy networks with a secondary diamine, like DMHMDA, the network architecture is such that flexible ahphatic sequences are present as chain extenders between the crosslink points. In such architectures, the motions of the HPE units can develop towards other HPE sequences (either along the chain or spatially neighbouring) without involving the crosslink points in their cooperativity. Thus, with these systems a different nature of cooperativity exists compared to the other network architectures. The introduction of an antiplasticiser in such a local packing does not affect the cooperativity as much as with the densely crosslinked architecture, for the crosslinks are not so much involved. Once more, it is important to point out that the flexible nature of the aliphatic amines does not matter since the same behaviours are observed for fully aromatic systems with identical architecture [68]. 

---