Dielectric relaxation and aging effect in interpenetrating network polymers of poly(urethane)‐poly(methyl methacrylate)

The permittivity and loss of poly(methyl methacrylate) (PMMA) network crosslinked with trimethylol‐1,1,1 propane and its interpenetrating network polymers with 10, 34, and 50% (by weight) poly(urethane) have been measured from 100 to 400 K over a frequency range of 12 to 1 × 105 Hz. Two relaxation processes, γ and β, are observed in the PMMA network, and a third process, αpu, in the 10% poly(urethane) IPN. At higher concentrations of poly(urethane), the γ process is removed from the temperature‐frequency range of our study. Crosslinking in pure PMMA slows the segmental motions involved in the β process and raises its activation energy. Physical aging of the 10 wt% poly(urethane)‐PMMA causes its γ process to become indiscernible and the αpu process to become better resolved. A discussion of these results in terms of local regions of segmental motion is provided.