RELATIONSHIP BETWEEN MELT VISCOSITY AND DIELECTRIC-RELAXATION TIME FOR A SERIES OF EPOXIDE OLIGOMERS

Melt viscosity has been investigated for a series of bisphenol-A type epoxide oligomers with different weight-average mol wts (M(w)BAR), ranging from 388 to 2640. The temperature dependence of the melt viscosity is described by the Williams-Landel-Ferry (WLF) equation. The melt viscosity eta is correlated with both the direct current (dc) conductivity sigma and the dielectric relaxation time tau. The two relationships between these three properties, sigma . eta(k) = const (0.63 less-than-or-equal-to kappa less-than-or-equal-to 1.12) and eta/tau(l) = const (0.73 less-than-or-equal-to l less-than-or-equal-to 1.06), are experimentally derived. Both exponents, kappa and l, depend on the M(w)BAR of the oligomer. The lower M(w)BAR oligomer has the larger value Of kappa. The kappa value is close to unity for the low M(w)BAR oligomer, which agrees with Walden's rule, sigma . eta = const, applicable to most low mol wt liquids. The l value is near unity for the epoxide oligomer with higher M(w)BAR, than 2000, which means that the melt viscosity is proportional to the dielectric relaxation time. The low M(w)BAR oligomer (M(w)BAR < 2000), on the other hand, has a smaller value of l below unity. The result indicates that the melt viscosity is not proportional to the dielectric relaxation time for the low M(w)BAR epoxide oligomer, whose dielectric a-relaxation is not governed by the Debye equation.