Mechanical and dielectric relaxations of epoxide resins containing spiro-ring structure

Low-temperature relaxation behavior was investigated for a bisphenol-A and three spiroring type epoxide resins cured with aromatic and spiro-ring-type diamines. A new well-defined relaxation denoted here as the β′ relaxation was observed from 50 to 100°C for the spiro-ring-type resin systems in both mechanical and dielectric measurements. The peak height and the activation energy of the β′ relaxation were entirely independent of the degree of curing. It is concluded that the β′ relaxation is due to the motion of p-phenylene group adjacent to the spiro ring. The β′ relaxation was not observed in the bisphenol-A-type resin system.