Mechanical relaxation mechanism of epoxide resins cured with diamines

The mechanism of mechanical relaxation, which is observed between 50° and 90°C in epoxide resins cured with aromatic and alicyclic diamines, has been investigated by comparing dynamic mechanical properties and chemical structures of these networks. This relaxation is denoted here as the α′ relaxation. The occurrence of the α′ relaxation depends on the existence of p-phenylene groups, and is independent of the degree of cure in the cured epoxide resins. Moreover, the intensity of the α′ relaxation increases linearly with increasing the concentration of p-phenylene groups in the networks. From these results, it is concluded that the α′ relaxation of the cured epoxide resins is attributed to the motion of p-phenylene groups in the network structures.